[rollei_list] Re: FYI

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
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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.

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Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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