Archived posting to the Leica Users Group, 2001/03/20
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At 12:48 AM -0500 3/20/01, TTAbrahams@aol.com wrote:
>Mike, I would be careful with the rear mounted filter on the 12/5,6. Unless
>you make the tube shallow enough to have the filter literally touching the
>rear element, you might induce vignetting. The 'rays" coming out of the rear
>of a 12 are coming out in a steep angle, at least the corner ones. I would
>try it, of course, but I would not be surprised if you get degradation in the
>extreme corners. A better solution would be to get the 77mm filterholder from
>Voigtlander and go and talk to your local Movie Supply House. They can
>provide either Roscoe or other makes of filters in just about any spectral
>sensitivity. All you have to do is to cut the gel to an appropriate size and
>stick it in the 77mm filterholder. You could even cut a small slot in the gel
>to match the "see-through" slot in the filterholder.If you could find a
>defunct 77 filter and remove the glass, you could use the filter-ring as a
>template for cutting the filtergel and to hold the gel in place in the
>holder. I have a fetish for not using any filters at the back of a lens,
>unless the lens is designed for it. Rear elements are critical, any damage
>there shows up as a very distinctive mark on the neg.
> In any case, it could be an interesting image with the 12/5,6 and IR film.
>Talk about wide-open spaces glowing and the black sky! If it works, please
>post some images.
>Good luck,
>Tom A
Tom, you can't induce vignetting at the rear any easier than at the
front. Actually, with this lens being slightly retrofocus, the
maximum exit angle is actually smaller than the maximum entrance
angle, so filters at the back are slightly preferable, although the
point about damage to the rear element is well taken.
Most Movie supply houses carry acetate filters for lighting and few
carry a good selection of optical gels for the image path. Kodak or
Lee are the best sources for optical gels.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
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