On 01/10/2015 12:44, whisky-dave wrote:
On Thursday, 1 October 2015 11:11:29 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
Ah! I didn't appreciate that your use of "DoF" wasn't referring
to depth of field,

thre are two DoFs in PHOTOGRAPHY. Nowerdays most people that do
photography know of depth of field, when I stared in the 6th form
I looked DoF up in a photography book.

I'd never heard of depth of focus but a quick google has educated
me on that. Strictly speaking the "London Underground" sign marks
the position of the film, rather than the range of positions of the
film.

I think early cameras such as plate it was importan to make sure the
plate was in teh right place eraly cameras weren't acurratly made.

Early cameras had adjustments so you put your bit of frosted glass in
and adjusted it and then replaced the frosted glass with a plate and
took the picture.

Do you know what a technical camera is? You can still do that with one
of them and they aren't that old and are very precise and accurate.

where the lens would produce an acceptably sharp image, which I'm
sure isn't a constant and varies according to focal length of
lens.

I don;t think it does. if yuo have any camera with interchangable
lens all of tehm have to be in focus at the same point and that is
where the film or sensor is. In the old days yuo could take the film
pack out and replace it. If teh fiml/sensor is in teh wrong place the
picture will be out of focus. Those with difital camera don;t
consioder this and probley have never even throught about it.

The depth of focus is the otherend of the depth of field equation, you
change one and you change the other, you change the depth of field when
you change the focal length so you also change the depth of focus.
You don't change the focal plane as that is nothing to do with DoF.

Now I wonder why you have *two* of those marks.

Well, ones Depth of Field, which is almost always on the lens and
usually a little straight line mark rather than a symbol, and teh
other is depth of focus which is an indication of where the film
plane is, or where the film sits.

I was misled by the way you phrased it into thinking that they
were alongside each other, either on the lens or the camera, rather
than being two completely different things which happen to share
the same acronym.

Well I've yet to see a use for this in the digital photography
world.

The same as in the film world.

I've yet to see a compact with this mark, well a compact that doesn;t
have interchangable lenses.

Why do you keep bringing in compacts are you only going to teach using
film compacts?

Given that the plane of both visible and IR film will be the
same, it's nothing to do with that.

wrong. IR focus at a differnt point to visable light.

Yes, but the difference isn't a constant for all lenses.

it's mostly a function of focal lenth.

Its mostly a function of design and which glass is used in which
element. Mirror lenses are usually telephoto but bring all the colours
to the same focus.


so you couldn't mark it by a different film plane Underground mark
on the camera.

I know which is why I say it has nothing to do with the lens, which
is why it's on the camera, and why they put IR marks on lenes mostly
telephoto rather than WA.

that's because depth of field and depth of focus are different for
different lenses so you can't put it on the camera unless you put the
depth of field on the info screen as a guide like my compact does.
It knows what the zoom and focus is set to and can workout the depth of
field.


Instead you'd measure from the film plane to the subject and then
set your lens to the measured distance using the IR mark on the
lens rather than the visible mark. Or if you were focussing using
the viewfinder, you'd focus using optical light, read the distance
against the visible mark and re-focus slightly to set that same
distance against the IR mark.

Yep that's how I did it. I never used the DoFocus mark for IR. I used
it a few times for macro when calculatign guide No.s but I found
trial an error worked best.

What's it got to do with guide numbers?


By the way, digital cameras have the same mark as well, marking
the equivalent place: the location of the sensor as opposed to
the film - eg
http://imaging.nikon.com/lineup/dslr/basics/19/04.htm which
relates to DSLRs.

But that isn't a compact camera it has an interchangable lens.

I never said it was a compact camera. I should have modified what I
said to "digital *SLR* cameras have the same mark" to clarify that.
Mind you, I have seen a compact camera with a focal plane mark -
I've no idea what make/model it was, but I remember noticing it at
the time. And some video camcorders have the mark as well (as had
some Super 8 film cameras).

It does seem that those that have experince of film know far more
about these marks than those brought upo on digital cameras.

Only those who had SLRs as virtually all compact film cameras didn't
have them.


How standard is it for the tripod mounting thread to be aligned
with the focal plane.

I'd say never but I've never seen one.



You don't want it to rotate about the film plane anyway.


and the centre of the sensor/film so the camera always rotates
about the sensor/film? Looking at the three DSLRs that I can lay my
hands on right now, the tripod bush looks to be in about the right
place (*) but on my two compact digital cameras it's a fair way off
to one side; I'm not sure whether the Instamatic-type film camera
that I used to have even had a tripod mount.

Can;t see the3 point of doing that the tripod mount should be so the
camera balancies better on the tripod and not stressing anyhting.
It's why you have tripod mounts on telephoto lenses and not normally
on WA ones.



(*) It's about the right distance front-to-back to line up with the
focal plane mark and it's roughly aligned left-to-right with the
middle of the lens mount.

irrelivent to film or sensors the tripod mount is about balance or
it's most convient to put it.

There are good and bad places to put the mount, they are seldom put in
the best place, just the convenient place.

On 01/10/2015 14:28, NY wrote:


The only time when the precise position of the tripod mount is critical (as
far as I am aware) is when taking multiple overlapping photos eg for a
panorama. I have seen special brackets with knurled knobs to move the
rotation point accurately to the position of the sensor if the camera's own
tripod bush isn't in the right place, though I'm not sure how you calibrate
it. It is probably important for movie cameras where the geometry has to
remain correct when panning during filming so a subject moving on a
circular
path centred on the rotation point will remain in focus.

The place that you need to pivot around isn't the film plane.
There is a node inside all lenses where rotating about that point
doesn't change the perspective as the image moves across which it will
do if you rotate the camera around the film plane.

http://www.panohelp.com/panoramicpivotpoint.html



I agree that apart from this case, it makes sense to put the tripod
point on
the lens (if it's a heavy lens) for better balance.

On 01/10/2015 16:10, NY wrote:
"whisky-dave" wrote in message
...
How certain are you that "depth of focus mark" is the correct term
for the
"underground symbol" mark?

only 99.48567892%

In camera manuals it's described as "focal
plane". Depth of focus (like depth of field) refers to a *range* of
distances - either side of the focal plane (in the case of depth of
focus)



Yep as I said.

http://petapixel.com/2012/06/01/ever...-camera-means/


Actually that page describes the point as the focal plane or film plane
mark and doesn't use the term "depth of focus".


The only time when the precise position of the tripod mount is
critical (as
far as I am aware) is when taking multiple overlapping photos eg for a
panorama.

No don't agree there.

would yuo really mount this lens on yuor camera and use your camera
tripod socket.
http://www.amazon.co.uk/650-2600mm-D... _SR160%2C160_


There's a reason why long lenese come with tripod sockets even my M3
to EOS converter as a tripod socket.

I agree that it would be horrendously out of balance. It's one hell of a
lens. I wouldn't like to hand-hold something 2.8 kg in weight and as
long as that - no smutty comments :-) And with a 2x converter - with a
5200 mm lens you could probably almost have seen Neil Armstrong doing
his "great leap" ;-) If 50 mm is regarded as 1:1 magnification then this
thing is over 200x magnification. Camera shake, thermal currents over
long distances and optical quality might be a problem.

That is nearly as big as my 400mm f4 lens, I have to put a converter on
it to get to that sort of focal length so I would borrow the daughters
1800 mm f8 as its got better colour correction being a mirror lens design.

It weights in at 12 kg IIRC.

Not the sort of thing you want to lug about.

OTH she has a Sony with a 1200mm zoom which is easy to carry about.
Its far better for casual photography as you have far more chance of
getting the picture if you are moving about.

I did say "precise" and I meant it as opposed to approximate. For
balance you mount a heavy lens as close to the centre of gravity of the
lens+camera unit, but the exact position isn't too critical.

Where it becomes critical, so I am told, is when taking several
photographs to join together. And then you'd mount the camera to rotate
about its sensor/film point. The two different uses wouldn't really come
into conflict as you are unlikely to use a 2600 mm lens to take separate
images of a panorama!

You could use a single line scan camera, they work quite well.

to move the
rotation point accurately to the position of the sensor if the
camera's own
tripod bush isn't in the right place,

what do you mean by isn;t in teh right place why would a camera maker
not put the tripod mount not oin the right place ?

As I said earlier it seems from a very quick sample of cameras I can lay
my hands on that DSLRs (and almost certainly film SLRs) do put the
tripod mount at that point (Nikon D90, Canon 10D), but compact cameras
don't always (Canon SX260). But that's a very limited sample. I can't
find my older G9 compact to see where its mount is.

The camera maker can't actually put it in the best place as its
different for each lens.

On 01/10/2015 16:45, whisky-dave wrote:


I make it 104X with a FF sensor 166X with my EOS M3. I'm thinking of
buying one, but also considerign I:d be better off with a telescope.
I got some reasonable moon pics with my 70-300mm

It is a telescope, it probably isn't a very good one as you can cut
quality right down for photographic use as the sensors and film are
pretty poor when compared to the eye.

A telescope will probably have optics surfaced to 1/8 wavelength while
camera lenses are probably 100 times that.

Its why telescopes cost more. ;-)

"dennis@home" wrote in message
web.com...
On 01/10/2015 14:28, NY wrote:


The only time when the precise position of the tripod mount is critical
(as
far as I am aware) is when taking multiple overlapping photos eg for a
panorama. I have seen special brackets with knurled knobs to move the
rotation point accurately to the position of the sensor if the camera's
own
tripod bush isn't in the right place, though I'm not sure how you
calibrate
it. It is probably important for movie cameras where the geometry has to
remain correct when panning during filming so a subject moving on a
circular path centred on the rotation point will remain in focus.

The place that you need to pivot around isn't the film plane.
There is a node inside all lenses where rotating about that point doesn't
change the perspective as the image moves across which it will do if you
rotate the camera around the film plane.

http://www.panohelp.com/panoramicpivotpoint.html

Ah, OK. My mistake for mentioning what's turned out to be a total red
herring :-(

It seems that manufacturers positioning the tripod point roughly where the
sensor/film is coincidence and that rotating about that point doesn't make
much sense for panoramas or for movie work where you don't want perspective
changes as the camera pans.

On 01/10/2015 13:40, whisky-dave wrote:
On Thursday, 1 October 2015 12:56:50 UTC+1, dennis@home wrote:
On 01/10/2015 10:25, whisky-dave wrote:
On Wednesday, 30 September 2015 17:50:11 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I have a canon A1 film camera. http://tinyurl.com/phjla58

just to the left of the hotshoe the symbol that looks s little
like the london underground logo.

This is the DoF mark, for the camera, it's Not Depth of Field,
but Depth of Focus. It only appears on film cameras (perhaps not
all) it is where the film will lay aka film plane.

I think it was a hang on from the old days before SLR focusing.
This mark has NOTHING to do with the lens attached unlike Depth
of Field.

Ah! I didn't appreciate that your use of "DoF" wasn't referring to
depth of field,

thre are two DoFs in PHOTOGRAPHY. Nowerdays most people that do
photography know of depth of field, when I stared in the 6th form I
looked DoF up in a photography book.

Well go and read it again because you have it wrong.

then prove you're not talking ******** oh you can;t.

http://www.videomaker.com/article/13...depth-of-focus

DEPTH OF FIELD - The range of object distance within which objects are in satisfactory sharp focus, the limits being the establishment of a circle of confusion of greatest acceptable size.
DEPTH OF FOCUS - The range through which the image plane (the emulsion of the film) can be moved backward and forward with respect to the camera lens such as defined under the depth of field and circle of confusion. This term is often confused with depth of field and vice versa.

In common English, Depth of Field is what the photographer is interested in; it is what is in acceptable focus in front of the lens. Depth of Focus is what only a technician is interested in; it is what is in focus behind the rear lens element which the film or image sensor "sees."



Try and think about what it says and stop talking ********.

the DoFocus is the complement of DoField one at one side of the lens and
the other at the other side of the lens. Unless you are designing lenses
they have exactly the same effect and on a camera you change one and the
other matches it.

i posted that link so as to help you understand but you obviously can't
be bothered.

as I think a lot of other people had been using that abbreviation


earlier in the thread, but instead referred to depth of focus, more
commonly called focal plane. I wonder how many other people made
the same misunderstanding of what you were saying. If you'd
mentioned the crucial detail about "London Underground sign" I'd
have known what you meant and realised that you really *did* mean
on the camera rather than on the lens.


Now I wonder why you have *two* of those marks.

Well, ones Depth of Field, which is almost always on the lens and
usually a little straight line mark rather than a symbol, and teh
other is depth of focus which is an indication of where the film
plane is, or where the film sits.

That has nothing to do with either DoF.

Yes it has.

More ********.

Given that the plane of both visible and IR film will be the same,
it's nothing to do with that.

wrong. IR focus at a differnt point to visable light.

That depends on the lens,

not it doesn't IR always focus at a differnt point it's to do with the way light refracts through a glass lens.
Of course I realise you know NOTHING about such things.

More ********.



The focal length has to be corrected for all.
No the foacl lenght doesn;t need correcting.

the colours and you can correct for IR too but its usually only done for
specialist uses.

What do you mean by specialst use's you've no idea have you.
Have you ever used IR flim ?
Didn;t think so.

A mirror lens will bring all the colours including IR
to the same focus.

Mirror lenes aren't the standard lens for most cameras.

Who cares, it proves you wrong about the above.



What could the second mark relate to? I'm even more puzzled because
in
http://www.mir.com.my/rb/photography...topviewblk.jpg
I can only see one mark.

yes that's the flim/sensor plan, it's where the film is, so you can
measure the flim to lens distance and even the film to subject
distance.

Well you got that bit right.

I got it all right.

More ********.

On 01/10/2015 12:45, whisky-dave wrote:
On Wednesday, 30 September 2015 22:32:38 UTC+1, dennis@home wrote:
On 30/09/2015 12:15, whisky-dave wrote:


I have a DoF mark on my camera.
You don't even know what that is do you, or what it's for.

Well you don't as its not a DoF mark.

Before you teach photography learn something about cameras.

It is a DoF mark that's what it's called that's what it is.


More ********.

On 01/10/2015 13:53, whisky-dave wrote:


ou know nothing about teaching do you.

I know enough about teaching to know that teaching the stuff correctly
is a good starting point and being so pig ignorant that you won't listen
to someone who knows telling you what is wrong is not a good attitude
for a teacher.


I've told you what they were, because you have NEVER been in a teaching enviroment you will NEVER understand.

More ********.

On 01/10/2015 20:05, NY wrote:
"dennis@home" wrote in message
web.com...
On 01/10/2015 14:28, NY wrote:


The only time when the precise position of the tripod mount is
critical (as
far as I am aware) is when taking multiple overlapping photos eg for a
panorama. I have seen special brackets with knurled knobs to move the
rotation point accurately to the position of the sensor if the
camera's own
tripod bush isn't in the right place, though I'm not sure how you
calibrate
it. It is probably important for movie cameras where the geometry has to
remain correct when panning during filming so a subject moving on a
circular path centred on the rotation point will remain in focus.

The place that you need to pivot around isn't the film plane.
There is a node inside all lenses where rotating about that point
doesn't change the perspective as the image moves across which it will
do if you rotate the camera around the film plane.

http://www.panohelp.com/panoramicpivotpoint.html

Ah, OK. My mistake for mentioning what's turned out to be a total red
herring :-(

There are always new things to learn.
At least you want to learn unlike some.


It seems that manufacturers positioning the tripod point roughly where
the sensor/film is coincidence and that rotating about that point
doesn't make much sense for panoramas or for movie work where you don't
want perspective changes as the camera pans.

Its quite difficult to grasp the concept without proper explanations and
a few drawings. I wouldn't expect the average photographer to even know
about it. I would expect cine camera operators to know.

I hate to think what the next generation of photographers "know".

"dennis@home" wrote in message
eb.com...
http://www.videomaker.com/article/13...depth-of-focus

DEPTH OF FIELD - The range of object distance within which objects
are in satisfactory sharp focus, the limits being the establishment of a
circle of confusion of greatest acceptable size.
DEPTH OF FOCUS - The range through which the image plane (the
emulsion of the film) can be moved backward and forward with respect to
the camera lens such as defined under the depth of field and circle of
confusion. This term is often confused with depth of field and vice
versa.

In common English, Depth of Field is what the photographer is interested
in; it is what is in acceptable focus in front of the lens. Depth of
Focus is what only a technician is interested in; it is what is in focus
behind the rear lens element which the film or image sensor "sees."

As illustrated very nicely by the diagram
https://encrypted-tbn2.gstatic.com/i...My4vO0bTwyLldN
that I posted earlier.

Dennis, as far as you are aware, is Whisky Dave correct to call the "London
Underground" circle-and-bar symbol on most SLRs the "depth of focus" mark? I
think the symbol marks the position of the focal plane and that the DoFocus
is, as the explanation above says, a range of distances either side of the
lens's focus point; when the lens's focus point is the same as the focal
plane, the image will be in focus on the film/sensor.

Or is "depth of focus" ever used colloquially (and incorrectly) as a synonym
for "focal plane"?

On 01/10/2015 20:27, NY wrote:
"dennis@home" wrote in message
eb.com...
http://www.videomaker.com/article/13...depth-of-focus


DEPTH OF FIELD - The range of object distance within which
objects are in satisfactory sharp focus, the limits being the
establishment of a circle of confusion of greatest acceptable size.
DEPTH OF FOCUS - The range through which the image plane (the
emulsion of the film) can be moved backward and forward with respect
to the camera lens such as defined under the depth of field and
circle of confusion. This term is often confused with depth of field
and vice versa.

In common English, Depth of Field is what the photographer is
interested in; it is what is in acceptable focus in front of the
lens. Depth of Focus is what only a technician is interested in; it
is what is in focus behind the rear lens element which the film or
image sensor "sees."

As illustrated very nicely by the diagram
https://encrypted-tbn2.gstatic.com/i...My4vO0bTwyLldN

that I posted earlier.

Dennis, as far as you are aware, is Whisky Dave correct to call the
"London Underground" circle-and-bar symbol on most SLRs the "depth of
focus" mark? I think the symbol marks the position of the focal plane
and that the DoFocus is, as the explanation above says, a range of
distances either side of the lens's focus point; when the lens's focus
point is the same as the focal plane, the image will be in focus on the
film/sensor.

Or is "depth of focus" ever used colloquially (and incorrectly) as a
synonym for "focal plane"?


Dave is the only person I have ever known refer to it as the DoF.
If you google "depth of focus" you won't find any images with it either.

On Thursday, 1 October 2015 19:30:31 UTC+1, dennis@home wrote:
On 01/10/2015 12:44, whisky-dave wrote:
On Thursday, 1 October 2015 11:11:29 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
Ah! I didn't appreciate that your use of "DoF" wasn't referring
to depth of field,

thre are two DoFs in PHOTOGRAPHY. Nowerdays most people that do
photography know of depth of field, when I stared in the 6th form
I looked DoF up in a photography book.

I'd never heard of depth of focus but a quick google has educated
me on that. Strictly speaking the "London Underground" sign marks
the position of the film, rather than the range of positions of the
film.

I think early cameras such as plate it was importan to make sure the
plate was in teh right place eraly cameras weren't acurratly made.

Early cameras had adjustments so you put your bit of frosted glass in
and adjusted it and then replaced the frosted glass with a plate and
took the picture.

yes and/but how do you know this ?


Do you know what a technical camera is?

you mean a scientific camera ?

You can still do that with one
of them and they aren't that old and are very precise and accurate.

are yuo saying more accurate than a digital camera, so doesd this mean one of those film cameras is BETTER than a digital camera ?
So why were you asking me whether or not film is better than digital for anything ?



where the lens would produce an acceptably sharp image, which I'm
sure isn't a constant and varies according to focal length of
lens.

I don;t think it does. if yuo have any camera with interchangable
lens all of tehm have to be in focus at the same point and that is
where the film or sensor is. In the old days yuo could take the film
pack out and replace it. If teh fiml/sensor is in teh wrong place the
picture will be out of focus. Those with difital camera don;t
consioder this and probley have never even throught about it.

The depth of focus is the otherend of the depth of field equation,

No it isn't.

you
change one and you change the other, you change the depth of field when
you change the focal length so you also change the depth of focus.
You don't change the focal plane as that is nothing to do with DoF.

irrelivant and not even true.



Now I wonder why you have *two* of those marks.

Well, ones Depth of Field, which is almost always on the lens and
usually a little straight line mark rather than a symbol, and teh
other is depth of focus which is an indication of where the film
plane is, or where the film sits.

I was misled by the way you phrased it into thinking that they
were alongside each other, either on the lens or the camera, rather
than being two completely different things which happen to share
the same acronym.

Well I've yet to see a use for this in the digital photography
world.

The same as in the film world.

So it has no use then is that your claim.



I've yet to see a compact with this mark, well a compact that doesn;t
have interchangable lenses.

Why do you keep bringing in compacts are you only going to teach using
film compacts?

No the aim is to teach photography.




so you couldn't mark it by a different film plane Underground mark
on the camera.

I know which is why I say it has nothing to do with the lens, which
is why it's on the camera, and why they put IR marks on lenes mostly
telephoto rather than WA.

that's because depth of field and depth of focus are different

Yes they are I told you that, but both have the abbrevaition of DoF.

for
different lenses so you can't put it on the camera unless you put the
depth of field on the info screen as a guide like my compact does.
It knows what the zoom and focus is set to and can workout the depth of
field.

Rubbish the deapth of focus indicator doesn;t need top move depending on teh lens used. The lens is designed so that when focused at infinity the image is in focus at teh film plane for visable light.




Instead you'd measure from the film plane to the subject and then
set your lens to the measured distance using the IR mark on the
lens rather than the visible mark. Or if you were focussing using
the viewfinder, you'd focus using optical light, read the distance
against the visible mark and re-focus slightly to set that same
distance against the IR mark.

Yep that's how I did it. I never used the DoFocus mark for IR. I used
it a few times for macro when calculatign guide No.s but I found
trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output
at a particular distance, changing this distance means less or more intense light which means to cointoll this you need to adjust the aperature in most cases.


I never said it was a compact camera. I should have modified what I
said to "digital *SLR* cameras have the same mark" to clarify that.
Mind you, I have seen a compact camera with a focal plane mark -
I've no idea what make/model it was, but I remember noticing it at
the time. And some video camcorders have the mark as well (as had
some Super 8 film cameras).

It does seem that those that have experince of film know far more
about these marks than those brought upo on digital cameras.

Only those who had SLRs as virtually all compact film cameras didn't
have them.

yes I know and until I know what 'compact' camera witout an interchaable
or additional lens options, I can imagine why they'd bother or explain it.
I can expalin why Lieca brought out a camera with snake skin.

How standard is it for the tripod mounting thread to be aligned
with the focal plane.

I'd say never but I've never seen one.



You don't want it to rotate about the film plane anyway.

I don't care and I doubt many people care where the tripod mount it.
NOTICE I said people NOT photographers.



irrelivent to film or sensors the tripod mount is about balance or
it's most convient to put it.

There are good and bad places to put the mount, they are seldom put in
the best place, just the convenient place.

yep that's why I said, as people don't care.

On Thursday, 1 October 2015 19:55:27 UTC+1, dennis@home wrote:
On 01/10/2015 16:10, NY wrote:
"whisky-dave" wrote in message
...
How certain are you that "depth of focus mark" is the correct term
for the
"underground symbol" mark?

only 99.48567892%

In camera manuals it's described as "focal
plane". Depth of focus (like depth of field) refers to a *range* of
distances - either side of the focal plane (in the case of depth of
focus)



Yep as I said.

http://petapixel.com/2012/06/01/ever...-camera-means/


Actually that page describes the point as the focal plane or film plane
mark and doesn't use the term "depth of focus".


The only time when the precise position of the tripod mount is
critical (as
far as I am aware) is when taking multiple overlapping photos eg for a
panorama.

No don't agree there.

would yuo really mount this lens on yuor camera and use your camera
tripod socket.
http://www.amazon.co.uk/650-2600mm-D... _SR160%2C160_


There's a reason why long lenese come with tripod sockets even my M3
to EOS converter as a tripod socket.

I agree that it would be horrendously out of balance. It's one hell of a
lens. I wouldn't like to hand-hold something 2.8 kg in weight and as
long as that - no smutty comments :-) And with a 2x converter - with a
5200 mm lens you could probably almost have seen Neil Armstrong doing
his "great leap" ;-) If 50 mm is regarded as 1:1 magnification then this
thing is over 200x magnification. Camera shake, thermal currents over
long distances and optical quality might be a problem.

That is nearly as big as my 400mm f4 lens, I have to put a converter on
it to get to that sort of focal length so I would borrow the daughters
1800 mm f8 as its got better colour correction being a mirror lens design.

1800mm at f8 which lens is that. I want two so I can make a pair of binoculars for 3D photography



It weights in at 12 kg IIRC.

Not the sort of thing you want to lug about.

wimp ! :-)


OTH she has a Sony with a 1200mm zoom which is easy to carry about.
Its far better for casual photography as you have far more chance of
getting the picture if you are moving about.

I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast majority of pros use standard refractive lenses rather than mirrors.

On Thursday, 1 October 2015 20:04:59 UTC+1, NY wrote:
"dennis@home" wrote in message
web.com...
On 01/10/2015 14:28, NY wrote:


The only time when the precise position of the tripod mount is critical
(as
far as I am aware) is when taking multiple overlapping photos eg for a
panorama. I have seen special brackets with knurled knobs to move the
rotation point accurately to the position of the sensor if the camera's
own
tripod bush isn't in the right place, though I'm not sure how you
calibrate
it. It is probably important for movie cameras where the geometry has to
remain correct when panning during filming so a subject moving on a
circular path centred on the rotation point will remain in focus.

The place that you need to pivot around isn't the film plane.
There is a node inside all lenses where rotating about that point doesn't
change the perspective as the image moves across which it will do if you
rotate the camera around the film plane.

http://www.panohelp.com/panoramicpivotpoint.html

Ah, OK. My mistake for mentioning what's turned out to be a total red
herring :-(

it was an infra red herring it's why you didn't see it, you weren't focused :-P



It seems that manufacturers positioning the tripod point roughly where the
sensor/film is coincidence and that rotating about that point doesn't make
much sense for panoramas or for movie work where you don't want perspective
changes as the camera pans.

the original use of tripod mounts had nothing to do with panoramic photogrphy as it didn;t exist like it does in the digital camera today.

On Thursday, 1 October 2015 20:06:44 UTC+1, dennis@home wrote:
On 01/10/2015 13:40, whisky-dave wrote:


DEPTH OF FIELD - The range of object distance within which objects are in satisfactory sharp focus, the limits being the establishment of a circle of confusion of greatest acceptable size.
DEPTH OF FOCUS - The range through which the image plane (the emulsion of the film) can be moved backward and forward with respect to the camera lens such as defined under the depth of field and circle of confusion. This term is often confused with depth of field and vice versa.

In common English, Depth of Field is what the photographer is interested in; it is what is in acceptable focus in front of the lens. Depth of Focus is what only a technician is interested in; it is what is in focus behind the rear lens element which the film or image sensor "sees."



Try and think about what it says and stop talking ********.

Try talking to a photographer and NOT someone that think photgraphy started with digital camera.

On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is nit the same.

"whisky-dave" wrote in message
...
On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is nit
the same.

I think what WD is not saying is this: you need to know the exact distance
from the flash to the subject to use the guide number to calculate the
correct aperture. Rather than measuring from flash unit to subject, he's
measuring from focal plane mark to subject.

I've rarely used guide numbers because my flash units have either been
completely automatic, metering the reflected light through the lens, or else
have had a sensor on the flash unit which does the same job, in which case
you need to set the aperture manually according to an ISO versus aperture
scale.

The manual flash units I had used a rotating scale: you preset the ISO and
then found the distance and read off the corresponding aperture which does
the guide number calculation for you (in the same way that a slide rule
performs multiplication or division for you).

I tend to read the distance off the lens's focus scale rather than getting a
tape measure out, though at close distances (maybe less than a couple of
feet) accurate measurement may be a bit more important.

I'd have to google how exactly you use a GN. From memory it's something
like: every flash unit quotes a series of GNs for different ISOs and you
divide the GN by the distance to give the aperture (two GN values are
quoted, for feet and metres). That's the principle, even if I've forgotten
the fine details.


This is called *sharing* knowledge as opposed to trying to be superior and
saying "if you're not clever enough to know, I'm not going to tell you"
which is childish and unhelpful - I worked for a guy who thought that this
was a way of motivating people, whereas it does just the opposite for me.

On 02/10/2015 12:55, whisky-dave wrote:
On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is nit the same.


You don't want to answer because you don't know why its relevant.

"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.

On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.

On Friday, 2 October 2015 13:22:11 UTC+1, dennis@home wrote:
On 02/10/2015 12:55, whisky-dave wrote:
On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is nit the same.


You don't want to answer because you don't know why its relevant.

I was the one that mentioned it.

On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:


So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is nit
the same.

I think what WD is not saying is this: you need to know the exact distance
from the flash to the subject to use the guide number to calculate the
correct aperture. Rather than measuring from flash unit to subject, he's
measuring from focal plane mark to subject.

Actually you should use both, especaily if the flash isn't mounted in the usual place.
Light comes from the flash gun and the intensity of teh flash dimishes with teh inverse square law, hits the subject and travels back to the camera again obeying the inverse square law.


I've rarely used guide numbers because my flash units have either been
completely automatic, metering the reflected light through the lens, or else
have had a sensor on the flash unit which does the same job, in which case
you need to set the aperture manually according to an ISO versus aperture
scale.

Flashes are usualy (apart from ring and dedicated macro which I couldn't afford (being at school) are built with the subject to flash distance of around 1 Metre to 5+ metres or so.
When I used the GN it was for distances of about 1-6 inches, which means you've pretty much go to put them on manual. I also used manual when I was taking pictures of a baloon bursting.



The manual flash units I had used a rotating scale: you preset the ISO and
then found the distance and read off the corresponding aperture which does
the guide number calculation for you (in the same way that a slide rule
performs multiplication or division for you).

have you ever seen one go below 30cm ?


I tend to read the distance off the lens's focus scale rather than getting a
tape measure out, though at close distances (maybe less than a couple of
feet) accurate measurement may be a bit more important.

quite a bit more.
Didn;t have much succsess foudn the lighting too harsh and shadows
were a problem too.


I'd have to google how exactly you use a GN. From memory it's something
like: every flash unit quotes a series of GNs for different ISOs.

I only used the GN for 100 asa can;t remmebr altering it for difernt ASAs

and you
divide the GN by the distance to give the aperture (two GN values are
quoted, for feet and metres). That's the principle, even if I've forgotten
the fine details.

That sounds right haven't done those calculating in this milenium.


This is called *sharing* knowledge as opposed to trying to be superior and
saying "if you're not clever enough to know, I'm not going to tell you"
which is childish and unhelpful - I worked for a guy who thought that this
was a way of motivating people, whereas it does just the opposite for me.

Tomorrow I will teach him how to walk in a straight line, if I have the time.
He is a bit of a waste of time coming up with crap he doesn;t understand and does even attempt to prove it.

On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you DO NOT know what GNs have to do with exposure for differing flash to subject distances there's no point in going further.

On 02/10/2015 13:36, whisky-dave wrote:
On Friday, 2 October 2015 13:22:11 UTC+1, dennis@home wrote:
On 02/10/2015 12:55, whisky-dave wrote:
On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is nit the same.


You don't want to answer because you don't know why its relevant.

I was the one that mentioned it.



You claim your so called DoF mark on the camera is relevant to guide
numbers so tell us why?

On 02/10/2015 13:34, whisky-dave wrote:
On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.



How does that improve over lensbaby?

On 02/10/2015 13:34, whisky-dave wrote:
On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.


Do you know what the bokeh of a typical mirror lens looks like?

On 02/10/2015 13:20, NY wrote:
"whisky-dave" wrote in message
...
On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is
nit the same.

I think what WD is not saying is this: you need to know the exact
distance from the flash to the subject to use the guide number to
calculate the correct aperture. Rather than measuring from flash unit to
subject, he's measuring from focal plane mark to subject.

I know how guide numbers work and the camera distance and hence his so
called "DoF" mark is irrelevant.
Its down to how far away the flash is and as you know on camera flash
isn't very photogenic so you use an off camera flash and that can be at
different distances to the camera.


I've rarely used guide numbers because my flash units have either been
completely automatic, metering the reflected light through the lens, or
else have had a sensor on the flash unit which does the same job, in
which case you need to set the aperture manually according to an ISO
versus aperture scale.

The manual flash units I had used a rotating scale: you preset the ISO
and then found the distance and read off the corresponding aperture
which does the guide number calculation for you (in the same way that a
slide rule performs multiplication or division for you).

I tend to read the distance off the lens's focus scale rather than
getting a tape measure out, though at close distances (maybe less than a
couple of feet) accurate measurement may be a bit more important.

I'd have to google how exactly you use a GN. From memory it's something
like: every flash unit quotes a series of GNs for different ISOs and you
divide the GN by the distance to give the aperture (two GN values are
quoted, for feet and metres). That's the principle, even if I've
forgotten the fine details.


This is called *sharing* knowledge as opposed to trying to be superior
and saying "if you're not clever enough to know, I'm not going to tell
you" which is childish and unhelpful - I worked for a guy who thought
that this was a way of motivating people, whereas it does just the
opposite for me.

I don't think WD is like that, I don't think he knows.
All his answers are the sort of thing Rod comes up with after he has
googled what the other poster has said.

I think he would be a terrible teacher of anything especially
photography so i hope he doesn't really do it.

On 02/10/2015 15:20, whisky-dave wrote:
On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:


So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures
is nit the same.

I think what WD is not saying is this: you need to know the exact
distance from the flash to the subject to use the guide number to
calculate the correct aperture. Rather than measuring from flash
unit to subject, he's measuring from focal plane mark to subject.

Actually you should use both, especaily if the flash isn't mounted in
the usual place. Light comes from the flash gun and the intensity of
teh flash dimishes with teh inverse square law, hits the subject and
travels back to the camera again obeying the inverse square law.

The distance to the camera is irrelevant.



I've rarely used guide numbers because my flash units have either
been completely automatic, metering the reflected light through the
lens, or else have had a sensor on the flash unit which does the
same job, in which case you need to set the aperture manually
according to an ISO versus aperture scale.

Flashes are usualy (apart from ring and dedicated macro which I
couldn't afford (being at school) are built with the subject to flash
distance of around 1 Metre to 5+ metres or so. When I used the GN it
was for distances of about 1-6 inches, which means you've pretty much
go to put them on manual. I also used manual when I was taking
pictures of a baloon bursting.

Most flashes need a diffuser and filters when used that close as you
don't want to stop the lens down to a pinhole, then the GN is useless.

The manual flash units I had used a rotating scale: you preset the
ISO and then found the distance and read off the corresponding
aperture which does the guide number calculation for you (in the
same way that a slide rule performs multiplication or division for
you).

have you ever seen one go below 30cm ?

I have used one below 30cm but it had variable power and few other
useful features, it can even sync to the full speed of my camera even
though its a focal plane shutter.



I tend to read the distance off the lens's focus scale rather than
getting a tape measure out, though at close distances (maybe less
than a couple of feet) accurate measurement may be a bit more
important.

quite a bit more. Didn;t have much succsess foudn the lighting too
harsh and shadows were a problem too.


I'd have to google how exactly you use a GN. From memory it's
something like: every flash unit quotes a series of GNs for
different ISOs.

I only used the GN for 100 asa can;t remmebr altering it for difernt
ASAs

Ask a photographer to explain it to you.


and you divide the GN by the distance to give the aperture (two GN
values are quoted, for feet and metres). That's the principle, even
if I've forgotten the fine details.

That sounds right haven't done those calculating in this milenium.


This is called *sharing* knowledge as opposed to trying to be
superior and saying "if you're not clever enough to know, I'm not
going to tell you" which is childish and unhelpful - I worked for a
guy who thought that this was a way of motivating people, whereas
it does just the opposite for me.

Tomorrow I will teach him how to walk in a straight line, if I have
the time. He is a bit of a waste of time coming up with crap he
doesn;t understand and does even attempt to prove it.

"dennis@home" wrote in message
web.com...

You claim your so called DoF mark on the camera is relevant to guide
numbers so tell us why?

Ah, I thought I'd explained, Dennis.

WD was using the focal plane mark (what he calls the DoF mark) as a
measuring point for measuring the flash to subject distance, as an
alternative to measuring from the flash head to the subject.

The distance is needed for calculating the correct aperture - see
Applications section of https://en.wikipedia.org/wiki/Guide_number

f-number = GN/distance

Given that he was using very short distances, I'd have thought that flash
head to subject would be the more correct thing to measu beyond a couple
of feet, the error of an inch or two between the two distances would be
negligible.

The Wikipedia article says "The position of the camera is not relevant"
which I take to mean that you could have the flash unit in a separate place
to the camera (joined by extension flash lead to hot shoe) and the exposure
would be the same no matter how far away the camera was - all that matters
is where the flash unit is in relation to the subject.

I suppose this makes sense: if you illuminate a subject by a given set of
lights, then you don't have to change the exposure if you move the camera
closer or further away

On Friday, 2 October 2015 19:43:02 UTC+1, dennis@home wrote:
On 02/10/2015 13:36, whisky-dave wrote:
On Friday, 2 October 2015 13:22:11 UTC+1, dennis@home wrote:
On 02/10/2015 12:55, whisky-dave wrote:
On Friday, 2 October 2015 12:42:50 UTC+1, dennis@home wrote:
On 02/10/2015 12:16, whisky-dave wrote:

Yep that's how I did it. I never used the DoFocus mark for IR. I
used it a few times for macro when calculatign guide No.s but I
found trial an error worked best.

What's it got to do with guide numbers?

Flashguns have guide numbers which represent the light output at a
particular distance, changing this distance means less or more
intense light which means to cointoll this you need to adjust the
aperature in most cases.

So what's it got to do with guide numbers?

If you knew anything about photgraphy you'd know, taking pictures is nit the same.


You don't want to answer because you don't know why its relevant.

I was the one that mentioned it.



You claim your so called DoF mark on the camera is relevant to guide
numbers so tell us why?

The mark is NOT relivent to GN.
It is the place where the film or sensor is located.
THE GN is a numberthat represents the power of teh light from the flash
gun NOT the camera.

On Friday, 2 October 2015 19:46:54 UTC+1, dennis@home wrote:
On 02/10/2015 13:34, whisky-dave wrote:
On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.



How does that improve over lensbaby?


Whats a lensbaby ?

On 05/10/2015 10:16, whisky-dave wrote:
On Friday, 2 October 2015 19:46:54 UTC+1, dennis@home wrote:
On 02/10/2015 13:34, whisky-dave wrote:
On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.



How does that improve over lensbaby?


Whats a lensbaby ?


Its a tool used by photographers.

http://www.wexphotographic.com/search/?q=lensbaby

At least one of which is a 2 element planar lens like the kickstarter.

On Monday, 5 October 2015 21:51:08 UTC+1, dennis@home wrote:
On 05/10/2015 10:16, whisky-dave wrote:
On Friday, 2 October 2015 19:46:54 UTC+1, dennis@home wrote:
On 02/10/2015 13:34, whisky-dave wrote:
On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.



How does that improve over lensbaby?


Whats a lensbaby ?


Its a tool used by photographers.

So is there a differnce between photographers and peole that take photos/snaps.


http://www.wexphotographic.com/search/?q=lensbaby

At least one of which is a 2 element planar lens like the kickstarter.

so you don't need a mirror lens for bokeh, I knew this in the mid 70s Bokeh isn't new.

"whisky-dave" wrote in message
...
so you don't need a mirror lens for bokeh, I knew this in the mid 70s
Bokeh isn't new.

I never suggested that you did. I simply said that the bokeh of a mirror
lens was characteristic - a doughnut shape on any bright highlight which is
very out of focus, rather than a solid disc or solid polygon in the shape of
the lens aperture that you'd get with a purely refractive lens.

On Tuesday, 6 October 2015 12:32:28 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
so you don't need a mirror lens for bokeh, I knew this in the mid 70s
Bokeh isn't new.

I never suggested that you did. I simply said that the bokeh of a mirror
lens was characteristic - a doughnut shape on any bright highlight which is
very out of focus, rather than a solid disc or solid polygon in the shape of
the lens aperture that you'd get with a purely refractive lens.

If you knoew a little about photography you'd have know that bokeh isn't new,
and over 100 years old an nothing to do with mirror lenes, other than that mirror lenes made bokeh come back into the spotlight (sort of pun intented).

Which is why if you want to teach photography you do NOT start with a digital camera you can end with one of course.

"whisky-dave" wrote in message
...
On Tuesday, 6 October 2015 12:32:28 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
so you don't need a mirror lens for bokeh, I knew this in the mid 70s
Bokeh isn't new.

I never suggested that you did. I simply said that the bokeh of a mirror
lens was characteristic - a doughnut shape on any bright highlight which
is
very out of focus, rather than a solid disc or solid polygon in the shape
of
the lens aperture that you'd get with a purely refractive lens.

If you knoew a little about photography you'd have know that bokeh isn't
new,
and over 100 years old an nothing to do with mirror lenes, other than that
mirror lenes made bokeh come back into the spotlight (sort of pun
intented).

Which is why if you want to teach photography you do NOT start with a
digital camera you can end with one of course.

I'm puzzled. I haven't said anywhere that bokeh is new or that you only get
it with mirror lenses or that you need a digital camera or a film camera to
see its effects. Since it is basic optics, I'd expect it to have been known
about since early photography if not before that going back to the days of
the camera obscura. And since early cameras used larger negatives and
therefore longer focal length lenses for the same field of view, it was
probably more apparent on older cameras since a 50 mm *equivalent* lens on a
large plate camera will have shallower depth of field than a 50 mm for a 35
mm camera at the same aperture. It is also possible that the shape of
highlights and therefore the nature of the bokeh will have changed over the
years as lens design has been refined.

It is a feature of all lenses that out of focus objects are rendered in a
way that is characteristic of that lens. I've seen reviews and specimen
photos of lenses for many years which show that some lenses give a "nicer"
bokeh and others give a more intrusive bokeh. It so happens that mirror
lenses give a very recognisable doughnut-shaped blur on highlights which (as
far as I am aware) is not apparent on conventional refractive lenses -
something that I referred to in passing a while ago in this thread.

To the best of my knowledge, a film camera and a digital camera with the
same lens, the same size sensor and using the same aperture will give the
same picture, in terms of depth of field and the amount and "look" of blur
(bokeh). I can't see why you would learn more about bokeh with a film camera
than a digital, but if you think differently, I'd be most interested to hear
your reasoning.

In fact you don't even need a film/sensor to see it - it's visible on the
ground glass focussing screen of an SLR (film/digital) even before you take
a picture, though the graininess of the screen may obscure some of the
detail which may only be visible in the finished slide/print/digital
picture.

On 06/10/2015 11:01, whisky-dave wrote:
On Monday, 5 October 2015 21:51:08 UTC+1, dennis@home wrote:
On 05/10/2015 10:16, whisky-dave wrote:
On Friday, 2 October 2015 19:46:54 UTC+1, dennis@home wrote:
On 02/10/2015 13:34, whisky-dave wrote:
On Friday, 2 October 2015 13:22:37 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
I though the problem with mirrors is that you can't stop down to increase
deapth or field, Tjhey are fixed aperature) which is why the vast
majority of pros use standard refractive lenses rather than mirrors.

Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens!

I'm not sure yuo have to have a mirror lens for that either.
https://www.kickstarter.com/projects...-portrait-lens
I know someone that's brought one.



How does that improve over lensbaby?


Whats a lensbaby ?


Its a tool used by photographers.

So is there a differnce between photographers and peole that take photos/snaps.

I didn't say that.



http://www.wexphotographic.com/search/?q=lensbaby

At least one of which is a 2 element planar lens like the kickstarter.

so you don't need a mirror lens for bokeh, I knew this in the mid 70s Bokeh isn't new.



I knew before that I see you never did tell us what shape the bokeh of a
mirror lens was. Mirror lenses predate digital too so its got nothing to
do with your worthless digital is no good for teaching argument.

On Tuesday, 6 October 2015 18:18:11 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
On Tuesday, 6 October 2015 12:32:28 UTC+1, NY wrote:
"whisky-dave" wrote in message
...
so you don't need a mirror lens for bokeh, I knew this in the mid 70s
Bokeh isn't new.

I never suggested that you did. I simply said that the bokeh of a mirror
lens was characteristic - a doughnut shape on any bright highlight which
is
very out of focus, rather than a solid disc or solid polygon in the shape
of
the lens aperture that you'd get with a purely refractive lens.

If you knoew a little about photography you'd have know that bokeh isn't
new,
and over 100 years old an nothing to do with mirror lenes, other than that
mirror lenes made bokeh come back into the spotlight (sort of pun
intented).

Which is why if you want to teach photography you do NOT start with a
digital camera you can end with one of course.

I'm puzzled. I haven't said anywhere that bokeh is new or that you only get
it with mirror lenses or that you need a digital camera or a film camera to
see its effects. Since it is basic optics, I'd expect it to have been known
about since early photography if not before that going back to the days of
the camera obscura. And since early cameras used larger negatives and
therefore longer focal length lenses for the same field of view, it was
probably more apparent on older cameras since a 50 mm *equivalent* lens on a
large plate camera will have shallower depth of field than a 50 mm for a 35
mm camera at the same aperture. It is also possible that the shape of
highlights and therefore the nature of the bokeh will have changed over the
years as lens design has been refined.

Maybe is because you said
"Mirror lenses also have very characteristic bokeh. But I won't make
disparaging comments if people have to google to find out what bokeh is and
what is characteristic about that of a mirror lens! "

Only those that have never done photography wouldn't know the above.
Which is what makes photography differnt from deciding whether film or digital is best is irrelivant to photography that is the point.

It is a feature of all lenses that out of focus objects are rendered in a
way that is characteristic of that lens. I've seen reviews and specimen
photos of lenses for many years which show that some lenses give a "nicer"
bokeh and others give a more intrusive bokeh.

Irrespective of film or digital media, and mirror lenes.



It so happens that mirror
lenses give a very recognisable doughnut-shaped blur on highlights which (as
far as I am aware) is not apparent on conventional refractive lenses -
something that I referred to in passing a while ago in this thread.

Yes adn this was not considered to be a good thing unless you wanted bokeh.
I remmerb sports photographers not being 'keen' on it because iof it's distraction, it might have lokoed cool or arty but it was seen as a downside of a mirror lens rahter than an advantage.


To the best of my knowledge, a film camera and a digital camera with the
same lens, the same size sensor and using the same aperture will give the
same picture, in terms of depth of field and the amount and "look" of blur
(bokeh). I can't see why you would learn more about bokeh with a film camera
than a digital, but if you think differently, I'd be most interested to hear
your reasoning.

Because people knew about this some 100 years before the digital camera existed. People that knew about photography rather than comparing film to digital would know about this.


In fact you don't even need a film/sensor to see it - it's visible on the
ground glass focussing screen of an SLR (film/digital) even before you take
a picture, though the graininess of the screen may obscure some of the
detail which may only be visible in the finished slide/print/digital
picture.