Archived posting to the Leica Users Group, 2001/03/19[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
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 > firstname.lastname@example.org > *My toys! My toys! I can't do this job without my toys!* I've been recently told to my chagrin on good authority that a glass filter in the rear is more damaging to optical quality than in front. But a thin gel affixed deftly to the rear would not hurt optical quality* and that's how i would do it! mark Mark Rabiner Portland, Oregon USA http://www.rabiner.cncoffice.com/ *Especially since your not focusing through the lens perhaps. But that wide who knows?