kelton;
I ran a few tests that may interest you. Previous msg is edited and
copied here.
George M.
I tested several lenses for wide-open sharpness/lack of distortion
using a star field as the test subject. The star field for most tests
contained the very bright object, Jupiter, as well as more modest
magnitude stars.
Results: (Blank is did not test) All lenses MC unless noted.
Wide Open One stop down
21/2 - Some Coma Good
21/3.5-(SC) Slight Coma
28/2 -Slight Coma and very slight blue fringing Good
35/2 - Some Coma Good
50/1.2 - Coma
50/1.4 - Coma,slight blue fringe Good
50/2 macro - Good
85/2 - (SC) Some blue fringing
90/2 macro - Good.
100/2 - Slight coma
The 50/2 and 90/2 were the only lenses that proved sharp and
distortion-free when used wide open.The 50/2 macro wide open was
slightly better than the 50/1.4 at F/2. The distortive effects were gone
for all practical purposes on all lenses when closed down one stop.
The 21/3.5 was much better than the 21/2 wide open. However, the 21/2
at F/2.8 was better that the 21/3.5 at F/3.5.
The worst coma was exhibited by the 50/1.2 and 50/1.4
The blue fringing, of course, is chromatic aberation. I was less
surprised to see it on the SC 85/2 than on the MC 28/2.
The coma was seen mainly on the very bright objects - Jupiter and a
bright star of magnitude 1 or so. Lesser magnitude objects showed no
visible coma (thru an 8x loupe.)
That's it. Hope this is useful. .
kelton wrote:
>
> >Probably true -- during the same years, lens design went from a craft
> >done by "old masters" types to a CAD-assisted process done by engineers.
> I'd like to know more precisely, if possible, which years this shift
> occurred.
>
> >there's such a thing as getting too hung up
> >on the numbers, I think. If photography was merely about pulling lines
> >per millimeter, what a boring tedium it would be !
> I agree in principle, but with my interest in astrophotography, I find I
> ignore the grades, the stats, and the numbers at my own risk--one of the
> reasons I'm so grateful for Reese's careful testing. Photographing points
> of light on a dark background is an extreme test for any lens (comparable
> to the cat-fur idiom currently afoot in this list) and I have found a
> number of lenses that are not up to the task. In my experience, the
> "numbers" are a good guide to which lenses will perform well at night,
> and which will fall flat on their diaphrams. (My only wish is for even
> more in-depth testing of the entire inbred family of common aberrations,
> but I think Gary is burdened enough.) Numeric evaluations may not be so
> important to the majority who photograph in the light of the nearest
> star, but I can show you some unambiguously miserable, hideous, shameful
> failures that have been caused by the wanton misbending of distant
> starlight. Case in point--I never knew the true nature of my docile
> 50/1.4 until it viciously attacked several images I was taking of star
> fields. At the corners of the frame were not pinpricks of light, but
> seagull-shaped red-blue blobs! (Or UFOs?) My 100/2 on the other hand
> always behaves like a thoroughbred, even when galloping wide open. So I
> ask your indulgence to let me (and my ilk) be unreasonably fretful, picky
> and superstitious. I hope our snits don't annoy, but this stuff is
> *important* to some of us--I for one truly dislike wasting a night's
> hard-won imaging on a turncoat lens.
>
> On another subject: I've had a couple off-list & one online request to
> explain my oblique remark re the 180/2.8 (which I had couched carefully
> so as not to alienate myself). Again, this is from an astrophot's point
> of view, so please adjust your judgments accordingly. I read an article
> sometime between 1991 and 1997 (in perhaps an astronomy mag?) comparing,
> I believe, 5 or 6 fast prime lenses in the 180-200 range. Nikon, Canon,
> and Zuiko among others. The Zuiko 180/2.8 registered dead last. (Relax,
> Giles, the 180/2 was not tested). I should have clipped the article but
> it was a library copy and my conscience got the best of me. Perhaps
> someone can unearth this article and prove me a liar.
>
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