[Leica] New Leica M Stuff

[henningw at archiphoto.com (Henning Wulff)]

Hi Frank,

The MTF curves give some indication of the relative performance, but 
certainly not all. Zeiss put out a couple of brochures that give a 
very good general explanation of MTF curves. If you want me to send 
them to you, send me a note off-list.

The MTF curves give an indication of the point transfer function of 
the lenses, so if the solid lines (for sagittal structures) and 
dashed lines (tangential structures) overlap, a point light source 
will be imaged as a slightly diffuse circle. If both lines are at 
100%, the point will be imaged as a point. The lower the contrast 
value (%), the larger the diffuse circle; the more the two lines 
diverge, the more elongated the now oval diffuse circle becomes. This 
leads to flare and 'bleeding'.

All of this only applies at the plane of focus. Little about the out 
of focus imaging qualities can be deduced from these graphs. Also, 
testing protocols can vary quite a bit and still be 'accurate', so 
graphs from different manufacturers, or even different testers from 
the same manufacturer can't be compared reasonably.

There's a lot more to optics than these graphs can show, so they 
always have to be taken with a grain (kilo) of salt.

The Summilux at f/1.4 has the weakest performance (surprise, 
surprise!), but by f/2.8 is quite respectable and very close overall 
to that of the Elmarit ASPH. Especially the larger and medium details 
are rendered very well across the field, and if anything are rendered 
a bit better further out in the field by the Summilux than the 
Elmarit. Extremely fine detail has pretty good resolution but lower 
contrast than the Elmarit.

All the lenses are very good in the central 15mm at all apertures, 
with very fine detail rendered at high contrast; only the Summilux at 
the widest apertures falls off a bit here.

At f/4 there are actually only two categories in performance: the 
Super-Elmar and the others. The other three each have their strong 
points and their weak points (relatively), but the Super-Elmar is 
best. The Super Elmar has a very slight increase in performance at 
the edges at f/5.6, but for the most actually loses performance as it 
is stopped down.

So from the graphs the Super-Elmar is definitely the best, but the 
others are all outstanding lenses. The Summilux, for example, is a 
fair bit better at f/1.4 than the non-ASPH Elmarit was at f/2.8.

The Tri-Elmar is quite interesting in that at f/4 it's performance is 
quite similar to that of the f/3.4 Super Angulon at f/5.6, except the 
far corners of the T-E are better than those of the SA. The old f/4 
SA was noticeably worse than the f/3.4, and closer to the non-ASPH 
Elmarit in performance.

At present I have a number of 21's; the Summilux, the Elmarit-ASPH, 
the Tri-Elmar, the f/3.4 SA and the CV f/4. The CV is decent, but 
lacks the clarity of the Leica lenses and all samples I've tried of 
the CV have had some decentering, which I've not had with the Leica 
lenses. The CV is not bad, but it's just not as good. The SA isn't 
useable on the digital M's, so it's hard for me to really compare it. 
On B&W film I still like it, but it clearly is not a modern optic. 
The other three I use pretty much interchangeably. The Summilux has a 
bit more distortion than the others, and the distortion on the 
Tri-Elmar is a bit more strongly mustache-shaped, so the Elmarit wins 
here. At medium apertures they are largely equivalent for practical 
purposes, and I tend to carry one or the other depending on their 
other attributes. Since distortion can be corrected in software when 
necessary, it's not as big a deal anymore as it was in film days, and 
the other qualities are reasonably given priority.






At 7:38 AM -0700 6/22/11, Frank Filippone wrote:
>Henning... you are among the few LUGgites that can read and make sense of
>MTF charts.
>
>Can you give a quickie review of the MTF charts for the 4 x 21mm lenses?  21
>ASPH Elmarit, WATE, Summilux, and Super Elmar.
>
>I have always wondered their relative merits....
>
>
>
>Frank Filippone
>Red735i at earthlink.net
>
>
>  From the MTF graphs the new 21 looks as good as anything ever made at that
>focal length, but it's not perfect :-). Still has distortion, the sagittal
>and tangential curves don't cover each other, they're not all above 95 at
>40lp/mm, and there is significant light falloff.
>When will they ever make a perfect lens??? :-)
>
>
>
>
>_______________________________________________
>Leica Users Group.
>See http://leica-users.org/mailman/listinfo/lug for more information

-- 

       Henning J. Wulff
  Wulff Photography & Design
mailto:henningw at archiphoto.com
   http://www.archiphoto.com