Re: [Leica] focus shift due to filter?

[John Collier <jbcollier@home.com>]

The references to this matter that I aware of is in the "Legendary Leica
Lenses" articles by Dick Gilcreast in the LHSA Viewfinder. He mentions it in
the article on the 135mm Hektor and here is the relevant quote:

"The one caveat I should mention in using the Hektor is in the use of
filters with the lens in rangefinder mount. In common with most other long
lenses, Leica's as well as everybody else's, the glass in the filter will
change the infinity setting very slightly, making the lens focus just a
little beyond infinity at the largest apertures. It is well to either stop
down to moderate apertures or use reflex focusing when using filters at the
largest apertures at very long distances. I first noticed this effect with a
200mm f/4 Telyt many years ago, and it took a while to figure out what was
wrong. The effect in the Hektor is less than in the Telyt, but still
noticeable at infinity with the lens wide open."

I have not investigated this myself so I cannot confirm it.

John Collier

> From: "Austin Franklin" <austin@darkroom.com>
> 
> A claim has been made (elsewhere) that using a UV filter will cause a 'focus
> shift', which, would be more critical for a rangefinder...depending on how
> shifted the focus is.
> 
> What are the facts around this claim?  I take a Hasselblad with a 110/2, and
> a magnifying hood...critically focus on something ~3' away, and I don't see
> a focus change with a UV filter on or off...and all my Noctilux and Summilux
> images are dead on focus wide open...and I do use UV filters, and I do a LOT
> of close up work...I would think I'd see it there.
> 
> Perhaps there is some focus shift, but it is certainly not significant.
>