Archived posting to the Leica Users Group, 2001/03/20
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At 2:29 PM +1100 3/20/01, Mike Nicholls wrote:
>I have bought a 12/5.6 Heliar to use for infra-red (among other things).
>Would it be practical to use a 25A or 87 gel on the rear element of this
>lens, rather than dangle the big stuff off the front. I was thinking of
>making a snug fitting cap/tube to put over the rear element prior to
>mounting the lens. This would have the appropriate filter gel on one end. It
>would need to be firmly attached to stay put and not foul the shutter of
>course. The reason I am posting this is that I am not sure what effect this
>will have on the light path through the lens in terms of "better or worse"
>than on the front. The cost of a 77mm filter up front will be far more than
>a small diameter gel at the rear, and it will also be far less obtrusive.
>What is the cost though in terms of image degradation? Is it viable or not?
>
>Mike Nicholls
>Canberra, ACT
>Australia
>mikenic@cyberone.com.au
>*My toys! My toys! I can't do this job without my toys!*
This is quite feasible. For Kodak HIE an 87 or 89B gel on the back of
the lens would probably be a more practical solution than on the
front. Just put a small dab of glue on one edge of the lens mount to
hold the filter in place and cut a small circle of gel. I've often
put a gel behind a lens. In LF work it is common to put a filter
behind the lens, and gels don't cause any problems re: focus.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
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