[Leica] CoF and Macro

["Erwin Puts" <imxputs@knoware.nl>]

Dear Adrian,

I will try to answer your post:

>Oh dear Erwin - I seem to have erred! Well perhaps you can give us the low
>down on why Leica chose to use the Elpro approach for 1:1.1 to 1:2 for the
>100 APO.
Actually: performance with ELPRO lenses drops significantly, even stopped
down. They are however easy to use as not everyone has bellows or tubes. The
problem with any close-up or macro work is that you magnify the smaller
detail structures to a level where  you now see the details you could not
detect normally (that is the idea of close-up work), but the MTF values drop
rapidly at these magnifications. So your eye will note details not seen
before in normal situations, and your eye has no reference of what to
expect. And you magnify the details with  lowered MTF values. It is
therefore difficult to have a clear idea of what image quality to look for.
So you need to experiment to know what to expect.

>I did not say the APO 100 is a zoomlens design, rather that it is 'somewhat
>akin to a zoom' in that it has a focussing group of elements and another
>set, [which in this case are stationary]. I have a vague recollection of an
>interview with Lothar Kölsch in which he mentions zoom lens design as
>playing a part in the optical construction of this lens (his first for
>Leica?). I understand that one of the main advantages of the Elpro vs tubes
>on the 100APO is that it keeps the field very much flatter. Also why does
>Leica consistently recommend not using extension tubes with zoom lenses?

A zoom lens generally is not characterized by the fact that the optical
system incorporates moveable lens groups or elements. Of course: a zoomlens
has moveable groups. but that is not sufficient to make it a zoom lens. We
need variator and compensator and focussing groups, working together to make
a design a zoomlens. You can find an explanation of zoomlens principles at
my site in the review of the variolenses.
Your reference to Mr Kölsch is not known to me: I have read all his
interviews and articles, but this part has excaped my attention. You may be
confused by the intervew of Mr Kölsch about the Tri-Elmar, which is a true
zoomlens.
The APO 100 has a six element DG design and a two rear element lenses and
when focusing, the whole group of six  DG elements ,move relative to the two
fixed rear lenses. That is not a characteristic of a zoom lens. BTW: not Mr
Kölsch, but Mr Vollrath designed the 2.8/100.
I am not aware that the ELPRO lenses keep the field flatter and I do not
know where you did read the Leica recommendation about not using extension
tubes with zoomlenses and their expanation of it. I will investigate this
further.

>'The story' as you put it was 'IME' and I stand by it: I do not get as good
>results with IF and zoom lenses on tubes as I do with lenses where the
whole
>optical cell moves. With the 70-180 and the Canon 70-200 for example I get
>much better results using the Canon 500D closeup lens than tubes and
>likewise the 90 Summicron is quite usable on extension tubes whilst the
>Canon 100/2, an IF lens, is not: both are excellent lenses in regular
>shooting. None of the dozen or so zooms I have tried to use on extension
>tubes has offered usable results: far too much curvature of field. My
>experience is however limited to a handful of lenses and practical photo
>taking in the field and no theoretical exercises nor rigorous
investigation:
>for that I read and respect your reviews. I look forward to your
forthcoming
>book.

I have nothing to add about your experiences with these lenses. I fully
trust your observations here. That zoomlenses bring bad results, is I
presume the result of the design priorities, which are not dedicated to
close up photography.
But as you say: your experience may happen to suggest a pattern, where there
might be a coincidence.
That is why I mentioned that you need to experiment as no general rules of
thumb are possible.
My comments were focused on tubes, not closup lenses. That is a different
area.
Thanks for sharing your detailed experiences. I will take them with me for
the next visit to Solms and dsicuss it there and keep you informed about the
results.

Erwin





In the meantime I wonder if you can help: my 90/2 R lens is a recent
secondhand purchase and I am surprised to find it has a quite different
colour balance to all my other Leica lenses. It is distinctly warmer in
rendition, even more so than the Noctiluxes which I have owned (1 and 1.2
which are the only recent Leica lenses to have been acknowledged to have a
non standard colour bias - to the warm side). I would say the shift is
similar to an 81a filter and is discernible in photos and even to the naked
eye looking through the lens. Can you explain how this came about - I am
told by Solms that it is not normal? In the meantime I find I rather like
it: it enhances the portraits I take with it and for which I bought it. Of
course with BW it is not an issue. I am not in any hurry to get it fixed but
wondered what might have caused this shift in colour balance if indeed it
has shifted from how it left the factory.

Bests