[rollei_list] Re: xenar test roll is back
- From: Newhouse230@xxxxxxx
- To: rollei_list@xxxxxxxxxxxxx
- Date: Thu, 4 Feb 2010 11:45:02 EST
I agree. Even the smallest amount of camera motion will degrade the
performance of even the finest lenses, and, in my opinion camera shake is a
far
greater cause of unsharpness than lens issues in most of our images.
Any lens test or comparison in the field is best done with the camera on
a sturdy tripod and a cable release attached. If no cable release is on
hand, activate the self timer so that your body is not in contact with the
camera or tripod during the exposure. That 10 seconds is also important to
let any vibration caused by you focusing, changing settings etc. to settle
down.
Though there are some folks with 'steady hands" (I am, unfortunately not
one of them) it's almost impossible to hold a camera without some minimal
amount of shakiness. I have known some photographers who claimed they could
shoot between beats of their own heart; I'm still working on that one!
In any case, hand holding a camera is fine for most purposes, (witness
Carlos' many excellent hand-held images) but not so good for judging
comparative performance at various apertures.
Charlie Silverman
In a message dated 2/4/2010 9:43:56 A.M. Eastern Standard Time,
daxelb@xxxxxxx writes:
Hi,
I suspect that's slower shutter speed is the true culprit in the softness
of your images. I have to say that I've never been able to shoot at less
than 1/100 with any camera without some evidence of camera shake. I would
retest shooting wide open at the faster shutter speeds.
Just my two cents,
David Baumbach
-----Original Message-----
From: Richard Knoppow <dickburk@xxxxxxxxxxxxx>
To: rollei_list@xxxxxxxxxxxxx
Sent: Thu, Feb 4, 2010 1:53 am
Subject: [rollei_list] Re: xenar test roll is back
----- Original Message ----- From: "Stephen Attaway"
<_stephen@xxxxxxxxxxxxxxxxxxx (mailto:stephen@xxxxxxxxxxxxxxxxxx) >
To: <_rollei_list@xxxxxxxxxxxxxx (mailto:rollei_list@xxxxxxxxxxxxx) >
Sent: Wednesday, February 03, 2010 10:10 PM
Subject: [rollei_list] xenar test roll is back
Hi all ...
Got the test roll I shot last weekend back. This was with my 'cord IV with
Xenar.
I did three wide open pix - good contrast, color and focus was spot on -
but frankly a bit soft.
Especially compared with the results stopped well down (f11-22). Sharpness
was really excellent and held well into the picture edges. Contrast was
moderate, giving a pleasing, classic drawing.
In fairness, I think there was just a touch of camera shake in the wide
open shots, because I was at 1/50 and am not quite used to the 'cord shutter
release. Later, in soft sunlight, with Provia 400x, I was up at 1/100 and
1/250 - and my handheld shots all looked like the 'cord had been bolted to a
granite plinth.
I even tried the Xenar with a Mutar 1.5x and bay I rings. The sharpness of
this combination was also very impressive, but contrast had dipped,
perhaps partly due to a touch of underexposure. I had opened up about 1/3 to
1/2
stop with the Mutar (I get good results that way with my Planar), but
should have opened up 2/3 of a stop to a full stop on the Xenar.
I'll post a few 100% crops from my scans this weekend, in case any of you
are also pixel peepers like me.
My conclusion: the Xenar is a fine performer stopped down but I'd be
reluctant to open it up past f5.6. Its really splendid at f11-22. The 'cord IV
is a very good match for Provia 400x, which is good because I bought way too
much of that stuff when it first came out.
And the 1.5 mutar is quite usable with the old 'cord, if you can overlook
the really nasty vignetting in the ground glass. Just a touch of vignetting
in the actual picture, though.
But I think I'll be using the 'cord IV more as a lightweight, less
imposing option to the 'big ride' for daytrips, with a minimum of accessories.
Its
obviously capable of really first class results, if you are aware of its
limitations and respect them.
And obviously there is nothing wrong with my Xenar ... no need to trade in
or trade up.
Thanks for everyone's help, advice and wisdom. I've learned a lot the last
few days.
Stephen
FWIW, the main residual aberrations in a well-designed Tessar type lens
are all reduced by stopping down. For many lenses of "normal" coverage the
residual aberrations are essentially gone over the field when stopped down
about two stops. For an f/3.5 lens this is around f/7 so stops of about f/8
or smaller should be quite good. The "optimum stop" may be somewhat smaller,
probably about f/11. Beyond this the loss of resolution due to diffraction
begins to become significant. This is the reason that lenses on small
camras rarely stop down beyond f/22 while those on large cameras often go to
f/32 or even f/45 to f/64. At f/64 a Rollei lens would be very blurred.
Beside the improvement in sharpness there may also be some improvement in
contrast as the optimum stop is approached. This is because spherical
aberration and its relatives like oblique spherical and coma also tend to
scatter some light and reduce contrast. For the most part well-designed
Tessars
do not have much residual spherical, mostly they have some oblique
spherical. This is similar to coma and, like coma, increases with image angle
and
decreses as the lens is stopped down.
Adding more elements is a way for the designer to control higher order
aberrations. For fast lenses, or wide angle lenses additional elements over a
Tessar are necessary if the lens is to have good performance and decent
speed. Note that some quite simple lenses (wide angle Protar) will cover
surprizingly wide angles (around 100 degrees) but onlyl at very small stops (c
f/64).
--
Richard Knoppow
Los Angeles, CA, USA
_dickburk@xxxxxxxxxxxxxx (mailto:dickburk@xxxxxxxxxxxxx)
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