[rollei_list] Re: Hello again, and a lens question

  • From: aghalide@xxxxxxx
  • To: rollei_list@xxxxxxxxxxxxx
  • Date: Fri, 11 Dec 2009 23:33:17 +0000

I recommend you get a book on optics by Kingslak. He worked for Kodak. Another book on camera optics written by C.B. Neblette is also good.
 
Ed Meyers
-------------- Original message from frank deutschmann <fdeutschmann@xxxxxxxxxxxxx>: --------------


> Hi everyone,
> It's been a long time since I posted here (though I will confess to
> occasional internet stalking); to much other stuff going on to keep up
> with this busy info-heavy list.
>
> Recently, I've been trying to improve my meager optical knowledge
> (knowledge of optics actually); to that end, I've been flipping through
> Ray's _Applied Photographic Optics_, mostly just looking at the pictures
> because math really isn't my thing. (Hey, I'm a quant working on
> subprime mortgages, what can you expect?!) As I know there are a few of
> you on here deeply immersed into optics, I thought I would drop by and
> ask a question....
>
> Anyway, Ray makes an interesting comment in Section 23.3 (pg 239 in the
> softcover 3rd edition):
> "When portrait lenses for large formats were of very long focus,
> up to 1m or more, a working aperture o f/16 gave an entrance pupil
> diameter comparable to the human interocular distance (IOD) of 63.5mm.
> This pupil area provides a large number of different viewpoints which
> integrate in the film plane to give a diffused image. This effect of
> stereo parallax is therefore not a true plane perspective but gives a
> psychological effect of 'roundness' or 'plasticity' which many people
> consider to be more natural than an accurate centeral perspective of the
> sitter. The small depth of field, giving progressive loss of image
> contrast to facial features and reduced sharpness, also contributes to
> this effect."
>
> Alas, this large number of integrated viewpoints and the IOD is not
> discussed anywhere else in this tome that I can find, so I am left with
> quite a few questions! (Incidentally, this is emblematic of this book;
> as large as it is, for me the book has inspired more new questions than
> answered existing ones, so quite an excellent book....)
>
> Avoiding the dreaded OT mark in the subject line, I will comment that I
> have particularly noticed the photos, particularly people, pet, and
> object portratits, that I have taken with my 180mm/2.8 tele-xenar (6008)
> often show this wonderful 3D quality, especially when looking at the
> bare chrome through a loupe on the light table. I get this effect with
> this lens more than any other, and on reading this passage I realized
> that shot wide open (typical for these portrait situations) the entrance
> pupil is within the realm of the IOD as Ray mentioned. This lens is
> certainly not the absolute sharpest I own, nor is it soft; stopped down,
> it is often overly harsh for subjects other than children and perhaps
> furry friends. Even now, seeing this 3D effect on the light table,
> through one eye, still impresses and fascinates me; it is at once
> pleasing and intriguing.
>
> So I'm wondering, is this roundness effect largely a result of the
> entrance pupil diameter, combined with pleasingly shallow and
> well-allocated focus depth? And, if so, given the multiple viewpoint
> aspect, am I right to assume that this is an effect concentrated in the
> part of the image which is just short of sharp focus? And, it seems to
> me that to maximize this effect, there's no substitute for large
> formats, as the distance to the subject needs to be appropriate for a
> pleasing perspective (so 180mm is pretty much the limit for MF
> portraits)?
>
> Can anyone point me to further reading on this fascinating subject?
>
> Thanks very much for your time, and I'm glad to see this list still
> exists!
> -frank
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