Hi Winsor et al,
I suppose I was asking for it, being vague.
> Unfortunately none of this makes any sense. Since 80 lines per mm is
> generally considered to be superb lens resolution I really doubt that
> Zeiss has discovered some alternative physics that produces 8 times
> the resolution of the best of any other manufacturers product.
>
> There are 25.4mm per inch. 600 lines per inch would convert to 23
> lines per mm which is not really good by anyone's standard. However
> it would probably put a nice image on large format film.
>
> Maybe you guys need to double check things? :-)
> - --
So I had to carry out a search; couldn't find the files I saved, on my HDD; so
now I have another set saved in the OM area.
I remembered wrong. The Zeiss Sonnar will do 250 lines per mm (not the 600
I quoted - maybe that was a film I was remembering).
Read about it at
http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=0013uk
and there is an excellent paper on what lenses and film can manage at
http://people.smu.edu/rmonagha/mf/lenslpm.html
And, while I am on this topic, 35mm lenses NEED to be sharper if they are
to compete in the sharpness stakes with medium format.
Consider two cameras, one 35mm and the other with a 6x9(cm) negative.
For the moment, lets pretend that the negative sizes are the full size as
above - and we know they are usually significantly less.
On the long axis, one has 35mm of negative, and the other has 90mm.
Suppose each camera is to photograph a subject that is 1 metre on the long
axis. That is, 1,000mm. And suppose each the lens of each camera has a
resolving power of 50 lines per mm.
So the 35mm camera uses 35 x 50 = 1750 lines in total to record what is on
1,000 mm of subject; 1.75 negative lines per subject mm.
The 6x9 camera uses 90 x 50 = 4500 lines in total to record what is on
1,000 mm of subject; 4.5 negative lines per subject mm.
Thus, even with lenses of equal resolving power, the 6x9 produces an image
with 4.5/1.75 = 2.57 times more detail.
The Zeiss Sonnar, if fitted to a 6x9 (and if it had the covering power, which I
doubt) would produce in absolutely optimum conditions, 90 x 250 = 22500
lines, or 22.5 lines per subject mm. In practical terms, optimally, fitted to a
6x6 body, it should be able to lay down 15000 lines on the 6cm negative, or
15 lines per subject mm or 8.75 times more than my hypothetical 35mm
lens.
However, as we all know, that is not the whole story, and versatility,
photographer skill, and many other factors contribute to successful results
with the 35mm system.
Brian
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