[Leica] MTF comparison

[Erwin Puts <imxputs@knoware.nl>]

Dominique wrote in part
>But, if we compare MTF tests published by Leica, between the 35 asph and the
>tri-elmar at a focal length of  35 mm, and both the 2 lenses at 5.6, we
>observe that the 35 is clearly the winner.

Well I have the Leica graphs in front of me and I wonder how this 
inference can be drawn. Look at this:

5lp/mm:identical for the Tri-E at 35mm focal length  and the asph 35 
from center to image height 21.6mm
10lp/mm: on axis the TriE has slightly better contrast, at the 21.6 
position the asph is slightly better
20lp/mm: the Tri-E is better than or equal to the asph from axis till 
image height 15mm, after that the asph is better.
40lp/mm: from axis till 6mm image height: tri-E wins, from 6mm to 
12mm the asph has an advantage, from 12mm to 15 they are equal, after 
that the asph is better. But the area from 6 to 12mm where the asph 
scores a bit better there is much more astigmatism to be seen so it 
is not an unqualified :better".

 From these figures it is impossible to conclude that the "35 is 
clearly the winner". Only if you give 100% of your personal score to 
the unimportant area at image height 20mm then the 35 wins. At more 
relevant image zones from axis till 15 to 18mm, the Tri-E is as good 
as or even better.
The MTF comparison will tell you that both lenses at 5.6 deliver 
outstanding image quality with of course some character differences.

But if someone just wants to prove the Tri-E to be not as good he 
will interpret the facts with this view in mind. As some scholar 
noted ages ago: if a person wants to distort reality, no amount of 
facts will stop him.


On the 2 versus one aspherical surfaces. It were Zeiss engineers who 
told me that, not Leica engineers.
On the image quality: the differences between the aspherical  and 
ASPH are so small as to be insignificant. There are some marginal 
differences (a shade higher contrast on axis for the first version, 
but better contrast in the field for the second version) but I wonder 
if any Leica user would be able to demonstrate this in even the most 
demanding of test situations.

Erwin