[Leica] Focator report

[Erwin Puts <imxputs@knoware.nl>]

Assessing an enlarger lens is different from the test of a 
photographic lens. An enlarger lens should translate the information 
content of the negative without any degradation and should be usable 
for its intended range of enlargement.
So I made two sets of test. One for an enlargement of  30 times and 
one for even bigger factors.
First the very big enlargements.
The Focotar 1:2.8/40mm at full aperture recorded more than 100 lp/mm 
(200 lines/mm) in the center with high contrast and very good edge 
sharpness. This performance held till about a diameter of 14mm. 
Beyond this the performance dropped rapidly to below 50 lp/mm. The 
edges and corners reproduced about 20 lp/mm with soft edge contrast 
but acceptable visibility.
Stopped down to 5.6 crispens the edges and contrast improves a bit, 
but the corners still are lagging.

The Apo-Rodagon 1:2.8/50mm at full aperture records more than 100 
lp/mm over the full picture area with a very high contrast till the 
farthest corners and a bitingly sharp edge contrast.
At 1:5,6 the reproduction quality improves even more.

At an enlargement of 30 times the Focotar covers an image circle of 
14mm with 100 lp/mm, high contrast and high edge contrast. Beyond 
that we see a reproduction of 50 lp/mm till the far corners.
At 1:5.6 the image improves and now we have a very crisp rendition of 
80 lp/mm over the whole image field, including the corners.
At 1:8 the recording capacity  approaches the 100 lp/mm over the 
whole image field.

The Apo-Rodagon at 1:2.8 is slightly better than the Focotar at 1:8. 
(That is more contrast, more resolution, higher edge contrast). At 1: 
5.6 the Apo is at its optimum and now  exceedingly fine detail is 
rendered with superb edge contrast.
Both had no signs of decentring or astigmatism.
The bottomline: At 1:5.6 and 1: 8 the Focotar within its intended 
range of 5 to 16 times enlargement is an outstanding lens.  It will 
reproduce the image quality of Leica lenses quite faithfully over the 
whole image field.
The full aperture is not recommended for really critical work as is 1:4.
The Apo-Rodagon will reproduce the  Leica quality a mite better, 
because of its recording capacity beyond 100 lp/mm. And here the 2,8 
aperture is really useable, even if f/4 would be advisable for 
excating work.

A note of caution. The many emails on the Lug  show that some Leica 
users are  not interested in the limits of  optical performance or 
are not willing to extract the possible image quality out of their 
lenses. As most users would be hard pressed to get the 40 lp/mm limit 
on the negative, the performance of the Focotar will support most 
demands. If you are looking for recording capacity on the cutting 
edge (an apt word here), the Focotar should be carefully tuned to its 
optimum settings. The user of the Apo-Rodagon will be served best and 
will be able to make that wallpaper print without compromises.

Erwin