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.