[Leica] A Tribute to Oolong, and Nocti wannabe

[pklein at threshinc.com (Peter Klein)]

Richard:  Remember, an RF is not an SLR.  The rangefinder has no idea what
aperture you are at, and its mechanism is independent of the lens'
characteristics.

The reason why I said "don't refocus" is that human error/inaccuracy can
slightly change the place the lens is focused on each time, muddying the
results.

Focus shift is that property whereby if the lens is focused on Point A
wide open, and you stop down without changing the focus setting, the lens
will now focus on Point B, which is usually a bit behind Point A.  As you
stop down, depth of field increases, and at some point it compensates for
focus shift. Usually at f/5.6 or 8.

But this makes the intermediate stops a problem.  With some lenses at say,
f/2, 2.8 or 4, you may find that you focused on someone's eyes, but in the
picture their eyes are sligthly blurred and their ears are in sharp focus.
 But if you'd shot wide open, the eyes would have been in focus.

The Noctilux has shift one can see even on film.  The 35/1.4 'Lux Asph has
shift we can see on the M8. Sean Reid has found that most fast aspherical
Voigtlander/Cosina lenses don't have significant focus shift. But their
standard spherical designs do, such as their 28/2.  I'm interested in the
50/1.1, and it's a spherical design, so I'm asking.

--Peter


-----------------
Peter to Richard & back...
> Nice shot, Richard. ?Next, how about a pancake? ?:-)
>

I can haz pancake!

> But seriously... Have you checked the 50/1.1 Nokton for focus shift on your
> M8. ?Very easy to do, just a couple of minutes on a tripod. ?Focus on a
> ruler, yardstick or focus target at 45 degrees and about 2 meters away.
> ?Take a shot at f/1.1, then without refocusing, do a series of all the
> click
> stops down to f/8 or f/11.
>

Wait a minute, is that what focus shift is? Why would anyone care
:-)??? Don't people focus on the aperture they use?

I will test it when I have a chance, but honestly, this sounds like a
non-issue?

> I'm very interested in this lens, but I'm not seeing any information about
> focus shift a the digital Ms. ?I know Tom A loves it, but he shoots film,
> which "forgives" focus shift significantly. ?I would be less interested in
> a
> lens that I can only use confidently wide open and at f/8.
>

But from your description, it sounds like if you "re-focus," then
there's no issue right?