[rollei_list] Re: FYI
- From: "A. Lal" <alal@xxxxxxxxxxxxx>
- To: <rollei_list@xxxxxxxxxxxxx>
- Date: Sat, 31 Dec 2005 17:00:53 -0500
Not sure what you mean Richard.
These show standard data, i.e. contrast in % (on the Y axis) as a function
of radial displacement from the optical axis (on the X-axis) for tangential
and sagittal rays at 10, 20 & 40 lppm.
Z did pioneer this, TTBOMK.
----- Original Message -----
From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Saturday, December 31, 2005 4:43 PM
Subject: [rollei_list] Re: FYI
----- 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
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