[rollei_list] Re: FYI
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Sat, 31 Dec 2005 13:43:29 -0800
----- Original Message -----
From: "A. Lal" <alal@xxxxxxxxxxxxx>
To: "Leica Users Group" <lug@xxxxxxxxxxxxxxx>;
<rolleiusers@xxxxxxxxxxxxxxx>; <rollei_list@xxxxxxxxxxxxx>
Sent: Saturday, December 31, 2005 1:14 PM
Subject: [rollei_list] FYI
An interesting read:
http://www.imx.nl/zeiss.html
---
Rollei List
Sometime I would like to see an interview with a Zeiss
"engineer" by someone who understands optics.
The MTF curves shown, which I can barely read, appear to
be lines pairs per millimeter plotted aginst image image
hight or perhaps angle. The l/mm appear to go up to 40
lp/mm.
There are two ways of plotting an MTF graph. One is the
way shown in these graphs and most other manufacturer's
published data. The other way is to show lines per
millimeter from 0 up to some limit, say 200 for several
image angles and f stops. Both are valuable but the second
shows data, such as maximum resolution and whether the the
lens has good contrast which can not be found from the first
graph.
Radial and Tangential resolution are ultimately limited
by diffraction at the stop. Because the stop is "distorted"
off axis the curves are not the same with radial resolution
falling off faster than tangential. These are continuous,
smooth, curves when only diffraction is present but can have
bumps and dips when combined with residual aberrations.
I am always troubled by superlatives applied as they are
in this story. I have no doubt that the Conterex lenses are
very fine, they certainly have a good reputation, but
whether they are finer than excellent lenses of other
manufacturers is IMO an open question, not settled by the
data in this article. It would be interesting to know if the
curves were measured or calculated.
As far as the mounts being superior I would like some
specifics.
I once had a chance to buy a Conterex kit with several
lenses for $150.00. Every one of the lenses had serious
element separation. Due to what? I have no idea. The lenses
are cemented with modern synthetics. Its possible to get
separation because the cement was not applied or cured
correctly or, possibly, because of very consierable
mechanical shock. In any case, it was enough to put me off
despite the seeming bargain.
Several Zeiss articles I've seen lately from posted links
appear to have been written by advertising or sales division
people who have mis-interpreted what they were told by the
technical people or didn't understand it.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
---
Rollei List
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