Re: Focus Shift with SFX200

[Welch <Bill.Welch@pressroom.com>]

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.

Good luck,

Bill


George Huczek wrote:
> 
> I want to try some Ilford SFX200 with a 50 Summilux-M on an M6, using a red
> filter.
> Is is necessary to compensate focusing for IR light, and if so, how do I
> determine how much to shift the lens?  Anyone tried this with IR film?
> 
> -GH