Hi Jim, Andrew, Moose, Dawid, Chris and all,
From: "Jim Nichols" <jhnichols@xxxxxxxxxxxxx>
>I have been experimenting with a Ross London lens dated around 1890, but
>designed much earlier.
Oh yes, I've seen your lens and your interesting results with it. I haven't
got such old lenses; my oldest one was a hazy, heavily scratched Leitz
Summar 50/2 from 1936 (#313xxx) -- sample pic taken on Bessa-T without
viewfinder: <http://cjss.sytes.net/post/summar.jpg>
But I replaced it for a better performing Canon Serenar 50/1.9 (circa 1950).
And also a bunch of Russian RF lenses (late 50's - early 60's)
From: Andrew Fildes <afildes@xxxxxxxxxxxxx>
>Don't forget Topogon....everyone forgets the Topogon.........
Sure! And the Hologon ;-)
Some say the Topogon inspired the design of the Russian Orion-15 (28mm f/6).
I had one of those and compared it to the CV Skopar 28/3.5 -- there was no
obvious difference, but f/6 is too limiting so I sold it. Now that I'm aware
how *sharp* the CV 28/3.5 is, the Orion was a great lens indeed!
From: Moose <olymoose@xxxxxxxxx>
>And the cause of the flare, reflections, also reduces the light getting
through the lens. >Reflective loss at an
>air-glass interface starts at 4% for crown glass and goes up from there.
Yes, you're right.
>Six individual elements means 12 air-glass interfaces. With a mix of crown
and flint >glass, that's a loss of say 5% x 12
>= 60%, a whole stop. F/4 becomes t/5.6
Well, it's not as simple as 5% x 12 -- each air-glass surface loses 5% of
the light _it_ receives, not from the total light entering the system. I'm
not good at maths, but I believe it should be something like 0.95 ^ 12 = 54%
transfer (or 46% loss). Anyway, about a full stop, as you predicted ;-)
>PS: I just ran spel chuck, and it suggested I replace Santisteban with
Obscurantist.
ROTFLMAOL!!!
From: Dawid Loubser <dawidl@xxxxxxxxxxx>
>I absolutely love printing negatives taken with the 50mm Heliar f/3.5 -
>I printed these two this week-end. Both shot wide open. All
>aspects of image quality is extraordinary with this lens
As Tom Abrahamsson said: "If you want no distorsion, no vignetting etc - get
a Heliar 50f3.5 and a tripod."
And if it has a pleasant rendering too, what's not to like... if you don't
need the speed? ;-)
From: Chris Crawford <chris@xxxxxxxxxxxxxxxxxxxxxx>
>My current favorite 50 is the ZM 50/1.5 C-Sonnar.
Wow! I think it keeps one of the cemented *triplets* of the original Sonnar,
which was yet another formula in order to keep within three groups for
reasonable flare (when uncoated)
I've got a Russian copy of the original Sonnar 50/1.5, the Jupiter-3.
Unfortunately, the rangefinder cam is misadjusted :-(
>Mine's optimized for focus
>accuracy at f2.8 and below, so I have never used it at f2 or 1.5 except a
>couple tests to confirm the existence of the focus shift that Sonnars have.
Aha! I always thought that 'focus shift' was simply caused by spherical
aberration, *if* and only if it's focused on the 'maximum _contrast_' plane;
but the maximum _resolution_ plane should remain the same at all
abertures...
However, I noticed pretty much the same issue of the modern Sonnar in my
Jupiter. Very intriguing...
Cheers,
--
Carlos J. Santisteban Salinas
IES Turaniana (Roquetas de Mar, Almeria)
<http://cjss.sytes.net/>
--
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