Chapter 2
Leica R-Lenses
9
The graphs for 2.8 and 5.6 indicate an improvement for the
20Lp/m and the 40Lp/mm, but the jumps are quite small.
Compare the jumps in performance of the Summilux. The resi-
dual aberrations of the Apo-Summicron are already so low at
full aperture that stopping down only improves the depth of
field. At smaller apertures the internal reflections are reduced
and the extreme edge rays are blocked. If you look carefully,
you may see the result of the diffraction at aperture 5.6: the
overall contrast for the 5Lp/mm is slightly reduced compared
to the values at 2.8.
Distortion is low with 1% but may be visible on critical inspec-
tion and suitable subjects. The Summilux is better here.
0
5
10
15
20
Y'[mm]
0
20
40
60
80
100
[%]
Aperture Stop 2.8
0
5
10
15
20
Y'[mm]
-5
-4
-3
-2
-1
0
1
2
3
4
5
[%]
Relative Distortion
0
5
10
15
20
Y'[mm]
0
20
40
60
80
100
Aperture Stop 5.6
[%]
