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

  • From: Mark Rabiner <mark@xxxxxxxxxxxxxxxx>
  • To: <rollei_list@xxxxxxxxxxxxx>
  • Date: Fri, 11 Dec 2009 16:24:11 -0500

> Hi Frank:
> 
> That elusive 3-d quality used to be called 'plasticity'. I believe it can be
> caused by a lens which is well corrected for aberrations in the center but
> shows increasing aberrations near the edges. The effect is to overlay a
> sharp central image over a softer one covering the entire field. If you
> think like a designer who could not fix this, due to limits of materials and
> computational power...you might try to optimize the results. The effect of
> unsharp masking was known and in common use at the time.
> 
> To quote from Ivor Matanle: "The portrait of Mr Robert Cox was taken in 1974
> to mark his fifty years of service to his company ... with a 50mm f1.5
> uncoated Zeiss Sonnar, and shows perfectly the curious characteristic of
> defined yet slightly unsharp detail that makes the optical quality of
> classic lenses so attractive."
> 
> I believe the tele-xenar was a relatively simple four element design. I'd
> bet its pleasing optical quality is due to the designer aiming for
> plasticity, using experience and a few ray tracings as a guide.
> 
> --------------------------------------------------
> From: "frank deutschmann" <fdeutschmann@xxxxxxxxxxxxx>
> Sent: Friday, December 11, 2009 8:40 AM
> To: <rollei_list@xxxxxxxxxxxxx>
> Subject: [rollei_list] Hello again, and a lens question
> 
>> 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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>> 
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Plasticity
Unsharp detail
Unsharp mask

Throw them all together do we get a concept behind a Rollei lens?
I don't think so.

" Unsharp mask" is a viable concept in photography wildly different  in
practical use in digital verse film which it was a negative sandwich.
" Plasticity" and "Unsharp detail" is gobbledygook.

Some guy can write some article in a magazine about the wonderful "non
detail" in a transitional optic but would that capture the imagination of a
Zeiss or Schneider optical designer not in a million years.
These guys are going for the best corrected  cutting edge lens to put in a
camera, period.
They are not all caught up in the mythos propagated by popular magazine
writers for the optical design field.
They want to move on to the next design which does not have these wonderful
defects. They are not into loving the old designs for the complex and
wonderful defects that only a connoisseur would appreatate.

Is  "plasticity"  a concept the  Zeiss or Schneider  optical designers are
involved with?
Again no its popular photography magazine articles again.

Ivor Matanle I'm sure a great guy but from a quick check seems to be an
expert in  collecting old classic cameras.
I'd get my optical concepts from other sources more into the science end and
less caught up in nostalgia and mythos ends.
Optical design is not a smoke an mirrors deal.
Most photographers are excited by the images they get form an optic with a
few flaws a possible. Even the wonderfull ones.


Mark William Rabiner



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