Re: PHOTO-3D digest 1296

[P3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxxxx>]

Re: Wollaksak f/2.7, Triplets, resolving power etc. John B. Eric et al.

John B. Yes, you quoted back the paragraph I was refering too. I just 
wanted to point out that the quality of large format is not in the 
lenses but in the lack of enlargment of images that wouldn't stand much 
enlargement. Historically miniature camera lenses starting with the 
Leica had good design to enable them to be enlarged. The Cooke Triplet 
of Dennis Taylor of 1898 was a marvel that obsoleted the Rapid 
Rectilinear and is no way in inferior lens. Granted it doesn't cover as 
well until stopped down as a Tessar does at the wider openings. But this 
is more due to glass and improvements later. The Tessar was introduced 
as an f/6.3 lens and worked its way up to f/2.8 where it was considered 
lousy on a Rollei and great on a Realist. For medium format it needed 
another element e.g. the Planar or Ross Express (a Tessar with a 
3-element rear). The triplet was pooh poored as f/2 lenses and f/1.4 
lenses came along with six and seven elements. (But these elements 
didn't do a thing for the lens when it was at f/8 except to make flare)
They just provided the means to work at f/1.4 or f/2. The last Leitz 
Leica Elmar 9cm tele became a three element lens that when this was 
advertised stopped its sales dead due to dread of a triplet. Yet with 
the new glass is was superior to the regular Elmar (A Tessar with the 
diaphragm on element ahead, just after the front element.) So it still 
depends on the actual curves and glass..all tessars and triplets might 
not be equal if quality control not exercised. Incidentally f/2.8 is the 
next full stop after f/4 for from f/2  (e.g. 2 x 1.414=2.828 or 4/1.414=
2.828) The main advantage of f/2.7/8 is that is is a full stop from f/4
Most people do not realize that f/3.5 is not a full stop from f/4 when
guessing exposure. BobH


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