Archived posting to the Leica Users Group, 1997/07/07

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Subject: Re: Focus Shift with SFX200
From: George Huczek <ghuczek@sk.sympatico.ca>
Date: Mon, 07 Jul 1997 19:51:20 -0600

At 08:23 PM 07/07/97 -0700, you wrote:
>Hi George. I haven't used the Ilford SFX stuff, but I have used Kodak's 
>infrared in my Leica Ms. The Ilford captures a smaller amount of the 
>infrared spectrum than does the Kodak, so I would guess the focus 
>adjustment would be less, or certainly no more. Anyhow, just focus on 
>your subject, then move the focus a tad closer -- that is, move the lens 
>outward. On the 50mm Summicron, moving the focus point to about the f/4 
>or f/5.6 mark on your depth of field scale should do it. I presume the 
>Summilux is similarly marked.
>
>It sounds complicated but in practice it's not much of a bother. It's 
>usually a good idea to stop the lens down to f/8, f/11 or f/16, as the 
>depth of field will take care of the focus imprecision and give you a 
>nice fudge factor. As the best infrared effects take place in bright sun, 
>that should be easy to do.  I've had good success with the Kodak infrared 
>and a red Wratten 25 filter. It's a bit harder to handle than the Ilford, 
>though.
>
Thanks for the info.  I suppose that with TTL metering it will be pretty
much hit-or-miss as far as correct exposure is concerned.  Bracketing may
not be practical with the subject matter I am looking for.
   I'm used to those red dots on non-Leica lenses, which show how much to
shift the lens at infinity.  It should be interesting to see what happens.
I'll try to see how much a slight shift of the lens throws out the
rangefinder image, so I can guestimate the focus on the fly and use a small
aperture to allow the extra Depth of Field to bail me out as needed.

- -GH