Re: BAS lens tests( reply)

[Erwin Puts <imxputs@knoware.nl>]

>When I had the honor to accompany Mr. Schulze during Photokina 1994, where he
>visited both the Leica and the Zeiss booth, the people there were not at all
>giving the expression that Mr. Schulze's test scheme is not good. In fact
>Leica has asked him several times to test their entire lens range for them.
Giving the status these tests have in Germany it would be foolish for the 
marketing people NOT to assign publicity value to these reports, even 
when factually incorrect.

>BAS does not use a TV screen instead of an optical instrument, this is
>rubbish. The BAS Pro test works - in brief - as follows. A highly defined
>slide (made by Zeiss, about 20.000$ worth) is being projected by the lens to
>a large screen. At that screen a high definition CCD camera analyzes certain
>areas of this projection, a computer compares the projected grid with the
>ideal grid. 
Maybe my description of a TV screen is not accurate enough. A projection 
screen however is a screen and has therefore a certain granularity. 
Analysing this projected image (which is nothing more than the same slit 
(0,03mm!) the Pop Photo guys use in their equally expensive lab setup) 
through a CCD camera (which certainly is a Videocamera!) introduces more 
image degrading noise. This setup is quite often used for quality control 
in all optic firms. It is also well known not to be a true equivalent of 
a real optic analysis. 
>
>The only people I know which are talking bad on BAS test results are the
>Normtest guys - they are the competition of BAS.
The Norm test persons from Color Foto (indeed the competitor of 
FotoMagazin) are right in their insistance that the MTF measurements of 
5, 10, 20 and 40 lp/mm are far superior to the crude circle of diffusion 
measurements and CCD translation method of BAS. 
In an interview in Color Foto (12/95) Lothar Kolsch, Manager of the 
Optics department at Leica has stated that the 5-40 lp/mm criterium is 
the best available at the moment. People from Rodenstock and Zeiss are of 
the same opnion. 
>
>It is my strong belief that there is not much sense in lens tests, when most
>lenese can be regarded as "very good". And my last remark: If you do not
>trust his results, you cannot trust any test results. So you have to find out
>if you think that the lens you are using meets your requirements. And if you
>personally think, that the lens you are using is the best in the world - it's
>okay with me. Everybody is free to believe what he/she wants.

The MTF test with its 5-40lp/mm (or for that matter the BAS slit analysis 
(which after all is an electronic equivalent of the age-old acutance 
test) fail to analyse important aspects of a lens (its colour 
transmission, its corner fall-off, its distortion, its distribution of 
resolution and contrast over the entire field, reflections, flare 
reduction etc).
All the BAS test does is comparing the the measurement of an edge 
gradient curve of an 0,03mm slit with its theroretical form. And that at 
one point of the lens. Neglected is also the quality difference at 
several distances (close-up, 1 meter, 5 meters 50 meters, and at 
infinity).
In my testing I weigh all these factors in the endresult. So for instance 
I analyse 15 points in a negative from center to corner at at least three 
different distances. So I have been able to show that some lenses are not 
gradually detoriating from center to corner, but that you can see 
distinct 'bands' of alternating better and less good definition. 
The eternal longing of people to have one number to qualify a product (or 
a person) is fundamnetally misguided. Who wants his or hers complex 
personality have reduced to a number measured along a one dimensional 
scale. 
Why then use this one dimensional measurement paradigm onto a lens, which 
also exhibits many characteristics of a strong personality.
Sorry for being so long winded. 
Erwin Puts