Re: [Leica] Heliar impressions

["Henning J. Wulff" <henningw@archiphoto.com>]

>In a message dated 6/18/99 3:58:49 PM Eastern Daylight Time,
>dmorton@journalist.co.uk writes:
>
><< Not sure where f16 came in WRT the Contax-mount Hologon, but that lens is
> f8, that's all, fixed, so f8 is both the maximum and minimum aperture of
> the Contax mount Hologon lens. >>
>
>I remember someone telling me that the Hologon vignettes so much that a
>graduated filter with a darker center fading to a clear outside is required
>to even out the light falloff.  If the edge falloff is 2 stops (f16) the
>filter would need to bring the center to f16 as well.  This is just hearsay,
>but it makes sense except that I've used the 15 f5.6 and later f3.5 Nikkors
>and they vignette some, but I never measured it at anywhere near 2 stops.
>Can't imagine the Nikkors could be better than Zeiss ; )
>
>
>DT

This has nothing to do with 'better than Zeiss'. Zeiss does just as well
with the 15/3.5 for the Contax SLR lens.

The Nikkors and all other SLR 15mm lenses are retrofocus lenses, and this
type of construction really helps the light falloff problem, while it
introduces others. The cos 4th law states that the 15mm Hologon lens will
only get 11% of the exposure at the center into the very corners, which is
about a 3 stop loss. Slight optical massaging reduces this very slightly,
and falloff of less than one stop is generally hardly noticeable, so my
Hologon with the 2-stop center filter behaves reasonably. My 15/3.5 Nikkor
has probably about a 1-stop loss in the corners, and my Heliar probably
about 1.5 stops falloff, which in practice doesn't look too bad to me.

BTW, I didn't mention it before, but the Hologons have no distortion, or as
close to none as any lens. All retrofocus lenses I have seen have some;
some very little, such as the Heliar and the 21ASPH, and some more, such as
the 15mm SLR lenses, and some a lot, such as the 18's from Nikon (all 3). A
symmetrical construction, which is what the Hologons (and the old 21SA)
are, are as distortion free as you can get. For architectural shots, that's
worth a lot.

   *            Henning J. Wulff
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