[Leica] Is 1999 Nocti have problem with M8

[henningw at archiphoto.com (Henning Wulff)]

At 10:14 PM +0700 4/3/07, Jerry Justianto wrote:
>Correct me if I am wrong:
>
>The way that I read is only the old Noctilux (and old 75 Summilux)
>that have focus shift problem with M8 but the new ones are not
>(include the recent 1999 Noct).
>
>JSJ

Focus shift is due to compromises made intrinsically to the design of 
lenses, and is not due to sample variations. All f/1 Nocti are of the 
same design and therefore will have similar focus shift. The only 
difference will be how your rangefinder is set up. That will, to a 
degree, determine how noticeable that shift is at various apertures 
and distances.

It has always been hard to nail the focus with the Noctilux, so a 
certain number of out-of-focus pictures have always been accepted, 
but now with immediate feedback and hi-res pixel peeping the issue is 
upfront and can't be ignored as easily.

Only very highly corrected, slow lenses with floating elements can 
really be accurately focussed over a range of distances at all their 
apertures. If you want high speed, you've got problems, especially if 
aspherics aren't employed, as focus shift is a spherical aberration 
issue. Then there are chromatic aberrations, which require apo 
correction to (partially) get under control. These, in conjunction 
with spherical aberration cause the focus shift to be different under 
tungsten light than daylight. Then there is the fact that lenses will 
not perform the same at different focus distances. So you have to 
introduce floating elements.

The 75/2 fully exemplifies this type of design, and it's also easier 
to do as it's an f/2 and has a narrower angle of view. In turn, it's 
probably the best performing lens on the M8, and truly shows what 
that camera can do.

So you would wind up with a Noctilux that would probably weigh a lot 
more, be bigger, and cost twice as much, and would have harsh bokeh.

I think sticking with the current design might not be a bad decision.

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