Archived posting to the Leica Users Group, 2001/03/19

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Subject: Re: [Leica] 12mm Heliar UW
From: Mark Rabiner <>
Date: Mon, 19 Mar 2001 23:28:09 -0800
References: <000101c0b0ee$fdcab840$189bfea9@hal2000>

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
> *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 Rabiner

Portland, Oregon

*Especially since  your not focusing through the lens perhaps. But that wide who knows?

In reply to: Message from "Mike Nicholls" <> ([Leica] 12mm Heliar UW)