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.