Hi,
Gary wrote:
"Modern and Popular Photography tests probably suffered from the same auto
diaphragm mechanism vibrations the show up in my OM-1(n) based tests!"
"By that, I mean that by the time an SQF grade of A is reached in my
testing, the resolution capability of the film itself has been maxed out.
I'm probably only seeing differences in contrast."
"My A-, A and A+ grades are so telescoped together by film limitations and
project lens limitations"
Well, here it goes: I have serious doubts if the results of Gary's test have
much to do with the quality of the lens...
What amazes me is that the thoughts quoted above not started a discussion
about the SQF rating itself. The main reason why I come up with this, is
that several times on this list lenses are judged by Gary's SQF rating. A
bad idea I think. Well, lets start with an example.
One of my favourite and highly under estimated lenses is the Zuiko 28-48/4.
It is a lens that only gets B's in the SQF. Here's a test from a Dutch
magazine:
http://members.nbci.com/_XMCM/photovoogt/pix/zuiko2848.jpg
and compare it with a test of the MC 50/1.8:
http://members.nbci.com/_XMCM/photovoogt/pix/zuiko5018.jpg
And now look at the SQF...
How is it possible that a professional magazine measures the lens as one of
the best zooms they have ever seen (in the 80s), with a resolution
outperforming almost every commercial film and even outperforming (in some
ways) the Zuiko MC 50 mm F1.8, while it is a lens with only B's...?
Also the contrast of the Zuiko 28-48 is famed by the magazine. As an example
here is a picture taken with the tiny wide angle zoom:
http://members.nbci.com/_XMCM/photovoogt/himachal/ezels.html (of course,
such a compressed and sunny picture doesn't proof much, but anyhow)
There is more.
In many of the SQF ratings the optimum of the lenses is found at fairly
small apertures, F11 or F16. This is not what you would expect and also not
consistent with the results of many professional tests. The optimum of most
lenses should be at F8 or sometimes even at F5.6. I suspect correct
focussing somehow plays a role within the SQF rating.
Another strange result is for example the B A B A serie with the 85/2. I can
not explain this result in optical terms. Most likely (external) vibrations
play a role here. May be passing by traffic? This sounds silly, but it is
not unlikely.
This brings me to another thing that amazes me: why not use a flash to
eliminate all vibrations? My own tests using Kodachrome 25 and a flash
showed that at F5.6 all my lenses reach the sharpness of the grain of the
K25, at the corner of the images. It was simply not possible for me to
notice an increase in sharpness from that point with all my lenses (primes
and zooms). I used a Leitz Colorplan 90/2.5 to project the images on a
smooth white screen. You need this to see the extremely fine grain of the
K25.
This is consistent with the calculated resolution of the lens and the film
combined. Even a K25 is not much sharper than about 125 lines per
millimetre. In this graph you will see that the influence of the lens on the
combined resolution is limited. (Note: contrast is a different story, but
again: films, hoods and filters have probably more influence on the contrast
than the lens!) http://members.nbci.com/_XMCM/photovoogt/pix/lensfilm.gif
(The graph shows curves for films with a resolution of 50 to 150 lines per
millimetre. I used the following formula: (1/combined)^2 = (1/film)^2 +
(1/lens)^2. This should be quite close to reality.)
Summarised:
- On a commercial film even cheap lenses should reach an A+ level at F5.6.
- Lower ratings at F5.6 - F11 must be caused by external factors.
- Since the SQF rating shows many B's at F8, the influence of external
factors
in the tests is in my opinion very large. I even think it is not possible
to
draw conclusions on trends like "the F2's are better than the F2.8's".
My conclusion:
Every Zuiko is an excellent lens.
Just take pictures instead of waisting time on discussing which Zuiko
performs better than the other!
OK, now I will be running for my life...
Bye,
Erwin Voogt
Utrecht, The Netherlands
http://members.ncbi.com/_XMCM/photovoogt/index.html
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