Archived posting to the Leica Users Group, 2000/10/26
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At 7:14 PM +0200 10/24/00, Pascal wrote:
> >Sorry to hear that. I'd be more interested in a 12 than a 35 from
>>another manufacturer.
>
>well, it's not as if the Ultra Wide Helar 12mm f/5.6 Aspherical were a
>bad lens, but I feel I could have been better when I see the chart.
>Optimum f-stop= f/8, with very good to good results.
>
>Lots of vignetting, however, even at f/11 where it is still one full stop
>and thus excessive. This is the real issue and will limit its practical
>usefulness.
>
>Pascal
>NO ARCHIVE
>
>---------
>Visit my photo pages at http://members.xoom.com/cyberplace
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><<< PGP public key available upon request >>>
As I noted before, the 21 ASPH has about one stop of falloff at f/8.
The 12mm Cosina has more than that, but both are useable lenses.
Dismissing a lens because it has more than one stop falloff is silly,
as almost every lens has that at its wider stops. The Noctilux has
more than 3 stops falloff at f/1, and many people still use it.
The 12mm has other issues having to do with the extreme differential
magnification issue at the corners, but the light falloff is truly a
minor point.
The easiest way to make a very wide angle lens with good eveness of
illumination is to make a retrofocus lens. The closest to the 12mm
Cosina that has existed is the 13mm Nikkor. It still has about 1 stop
falloff when stopped down to f/11, and also has distortion of the
oxbow kind, _lots_ of flare, and doesn't have anywhere near the
contrast or resolution that the 12mm has. This was from an admittedly
short (about 20 shots) trial with the 13, but it was fairly obvious.
It had similar performance, at a slightly reduced level, to that of
the first 15/5.6 Nikkor. The 15/3.5 Nikkor is a lot better, but
doesn't come close to the 15/4.5 Heliar or the 12/5.6 Heliar.
The Heliar might not be as good as the 21 ASPH, but it is 4/7 the
focal length, and it does not disgrace itself when used in
conjunction with that lens.
Shoot some pictures; you sometimes get a better idea of what is going
on than looking at simplified test results.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
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