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.