Re: Duplex 120 Image quality

[egoldste@xxxxxxxxxx (Eric Goldstein)]

At 11:34 PM 1/30/96, Ray Hannisian wrote:
>Tim writes:
>Also, one of my main interests in raising this issue is to find out whether
>something more recently built than a Realist, say a Belplaca (1955), would
>likely have lenses capable of that 'snap' I'm used to in my Duplex.  The
>Realist, while sharply in focus, did not.

We tend to like to discuss (and measure) lens resolution as an index of
performance here on the group...

You raise another important criteria for judging lens performance,
contrast. From time to time, some of the groups more technically
knowledgeable members will talk about the compromises and trade-offs lens
designers make in giving photographers a "look" the want, and resolution is
not necessarily at the top of the list.

Bob Howard reminded me in a recent piece of correspondence that companies
such as Leitz and Zeiss came to the conclusion that "contrastier" appears
"sharper" to the human eye some 35 years ago, and began designing
accordingly:

>After a Zeiss paper in 1970 or so saying it was a waste of time
>designing lenses with more than 40 lines per mm for "amateurs" who
>only made at most 4x6 prints, lens design seem to go for a large core
>with no flare in the "circle of confusion" to get high contrast and
>less resolving power. I think the original Summicron has the resolving
>power and doesn't fall apart in big blowups like some modern lenses.
>But it is hard to say what happens. I have a 16x20 RA-4 set of prints
>made from the Tamron 28-200mm zoom that ought to have a lot of optical
>faults considering the number of elements and compromises to get that
>zoom range..and I am amazed at the quality. What I think is the case
>is that contrast looks sharp when it really isn't and good resolving
>power looks fuzzy when contrast is poor. Zeiss has a famous picture of
>two playing cards..a KING showing the difference in some optical
>books.
>The fuzzy one actually has more detail when looked at close but looks
>like hell along side the high contrast one when viewed normally. BobH

In terms of my own experience, I can tell you that "snap" is the area where
most older lenses don't hold up as well as modern ones. One of the reasons
I won't let go of my old first production run realist (A3345) with Ilex
Paragon lenses is that they _appear_ sharper/contrastier than the cooke
triplets I have seen on other stereo cameras (comparable to my realist 2.8
at f/8 or above!). I suspect the reason is the unusually heavy optical
coating on the lens element(s?), something not found on the other 50's
cameras. The Ilex's don't "test" better than the other triplets in terms of
resolving power, they simply "look" better, and I'd bet it's attributable
to superior contrast.

On the other extreme, Verascope F40s are well known to have an interior
design that causes internal reflections from the lenses and produces _very_
flat, unappealing images with poor contrast (a condition which is
modifiable/correctable).

In terms of the Belplasca, it's been many years since I used one regularly,
but I remember the Tessars to be coated and excellent performers in terms
of center sharpness, edge sharpness and contrast. They will not be as good
as modern tessars fabricated with modern manufacturing methods/tolerances
and optical coatings, but they are probably the best your find in classic
stereo cameras...

But get out your wallet! I've been searching for an affordable one for
years, to no avail...they typically go for about $850 for a user and up,
up, up from there!


Eric G.
egoldste@xxxxxx



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