[Leica] Rangefinder error on M9

[hopsternew at gmail.com (Geoff Hopkinson)]

Howard I think you were given a lot of usefiul info on possible factors
(based on the very limited info from you) but no-one can definitively
determine the issue without some proper testing.

Cheers
Geoff
http://www.pbase.com/hoppyman
NO ARCHIVE


On 8 November 2010 05:51, Howard Ritter <hlritter at bex.net> wrote:

> Frank, Marty, Mark?
>
> Well, I don't know whether this is focus shift with stopping down or not,
> and I doubt I could determine this with tests. One would have to step the
> lens through the indicated focus point, examine the images highly 
> magnified,
> and determine where the maximum sharpness occurred. At f/16, it would
> probably take a mathematical analysis of the images and plotting of a curve
> to determine within a few percent where perfect focus is.
>
> My intuition is that the degree of defocusing is more than aperture-related
> focus shift would produce in any design that Leica would let into
> production. (Always was a pollyanna.)
>
> I think I'll just have to remember to rotate the barrel a millimeter to the
> near side when shooting at medium distances and wide apertures. And do some
> testing to see how far I have to stop down to be happy settling for what 
> the
> RF gives me.
>
> ?howard
>
>
> On Nov 7, 2010, at 6:02 AM, Frank Dernie wrote:
>
> > Hi Howard,
> > I think what you are seeing here is the effect of "focus shift". It seems
> many lenses have a shift in focus with aperture which is normally masked by
> the increasing depth of field with aperture closing, and, on film bodies, 
> by
> the effectively thick sensitive layer, since film emulsion is fairly thick,
> and the film rarely flat anyway, the focus will fall -somewhere- within the
> sensitive volume (it is not that much). A digital sensor is flat and
> therefore less tolerant of focus shift, the 90mm f2 apo has a tiny depth of
> field and at some apertures the plane of focus falls outside the depth of
> field due to focus shift.
> > It is also difficult to get perfectly in focus anyway, I use mine with a
> viewfinder magnifier.
> > A quick search on the internet will turn up quite a lot of discussion on
> this and the 90mm f2 apo-asph lens is one of the most sensitive lens out
> there for this problem - sadly.
> > The new 35mm f1.4 asph came out because focus shift on the existing lens
> was being noticed on the M8 and M9 when it was not using film bodies.
> > cheers,
> > Frank Dernie
>
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