Re: Lenses and Contrast

[P3D Dr. George A. Themelis <fj834@xxxxxxxxxxxxxxxxxxxxx>]

Sam the 3D Hacker hits again with another series of interesting questions
for the active 3D photographer of this list.  The same questions were going
through my mind TODAY, as I was evaluating the first roll out of my new
BELPLASCA.  The contrast was lower than that of my 2.8 Realist.  I used
both cameras and shot identical pictures.

>My theory about a low contrast lens is that
>stray light from dirt, internal reflections, etc tends to boost the shadow
>detail in a way similar to " flashing" to reduce contrast in prints or
>slides. Is this accurate? 

Yes, Sam, I think it is.  After I finished the first roll from the new
Belplasca, I opened the camera and checked the lenses (I should have done
it earlier, I know!!!).  I found out that the lenses were covered with dust
and humidity in the inside, which was cleaned easily.  

>If so, is it not possible to design a filter to
>reduce contrast in high contrast lenses?

Oh, yes!  It is actually called the "dirt and fog" filter! ;)  Seriously, I
use it in my SLR for slide bar shots.  Any dirty/fogged filter will smear
the light and reduce the contrast.  Some people think that a dirty filter
reduces sharpness.  I think it has nothing to do with sharpness.  It only
reduces the contrast by increasing the stray light, etc., as Sam described.

>A classic example of the effects of light "noise" in a stereo camera is the
>Verascope F40. I once did a test shot with a Belplasca and the Verascope and
>the results were amazing. The Belp shot was super crisp and contrasty, while
>the F40 was very muddy, but had better shadow detail. It turns out the
>Verascope has internal reflection problems as light bounces off the internal
>walls in front of the film window.

Yes, very good example.  There is a theory that the Verascope was designed
like that on purpose to create low-contrast "moody" pictures.  I am not
sure if Allan Carrano agrees with this statement but many times these
pictures are better than crispy ones, especially in projection.

>It seems to me there will be situations where you would want to vary the
>contrast while shooting, that's why I wanted to know if it's ever been done.

Yes, I run into these situations right now... and use my SLR for those.
Any filters placed in front of the lenses in a stereo camera must be well
matched, which is a problem.  It is easier to do it in one SLR.

BTW, I liked the lower contrast Belplasca shots.  The day was sunny and I
was shooting "Nostalgia" hence low contarst helped.  I'll let you know if
the crisp contrast returns now that I cleaned the lenses.  But I still
don't think that the Belplasca is sharper than my 2.8!!!

George the 3D FOGGY man.


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