Sounds good. I've noticed that the MTF choice for the DA8 50-135 is f4
at shorter focal lengths as well. It goes to 6.7 at the longest focal
lengths.
Paul
On May 11, 2009, at 11:42 AM, Margus Männik wrote:
Absolutely,
and this is probably why it shows so good results right from wide
open (at APS-C bodies).
One more interesting fact. As you may know, there is a MTF sub-
program at K10D and K20D (actually the setting have been there since
FA lenses and Z/PZ bodies appeared - for example Z-1p has it). In
this mode camera tries to use the "sweetest" aperture range of
attached lens. I do use it quite often as my normal shooting mode
and simply adjust aperture if I don't like what camera likes (Hyper
Program). Usually it means that camera is trying to keep the
aperture somewhere between f/5.6... f/8 or so, but you never see any
lens used wide open - even if there's no light at all. Now, when I
got DA*60-250 I was really surprised to notice, that camera quite
often decided to use f/4. I made a simple test and found out, that
in low(er) light situations (indoor at sunny day is enough) K20D MTF
program really chooses f/4 from 60-135mm and switches to f/5...f/5.6
at longer focal lengths. Z-1p preferred f/5.6 through the whole zoom
range.
Isn't it a clear message from Pentax optical engineers - the lens is
really good enough to be used (at APS-C bodies) wide open?
BR, Margus
(and sorry for my muddy english)
Paul Stenquist wrote:
So that would suggest that perhaps the DA 60-250 was designed to be
used with both formats. That would certainly be a plus.
Paul
On May 11, 2009, at 10:39 AM, Margus Männik wrote:
Unfortunately DA*50-135 doesn't fit FF. Wide open you can see dark
corners clearly at 50mm, vignette achieves the maximum at 70mm and
then reduces to mild falloff after 90mm (but you can still see it
at 135mm). Stopping down makes it worse and at small apertures you
can clearly see a round "imaging area" at all focal lengths.
BR, Margus
Paul Stenquist wrote:
True enough. I haven't tried my DA* 50-135 on full frame, but I
expect the results would be similar. I know the DA 50-200 covers
full frame. But if you believe Ned and the Pentax website, none
of these lenses were designed for full-frame use. As you point
out, the 60-250 may be different in that regard. Or not. Some of
those early roadmaps were full of confusing nomenclature.
Paul
On May 11, 2009, at 9:45 AM, Mark Roberts wrote:
Paul Stenquist wrote:
Well, there you have it. Only minor vignetting. Would that
increase or
decrease at a smaller aperture?
It's probably falloff, rather than vignetting, and it would
improve at
smaller apertures.
In any case, it's probably useable on full frame, although I
would
think it's optimized for APS-C.
Since it was originally designated the "D-FA 60-250" I expect it
was
designed for full-frame (they probably changed the designation
to DA
when they decided to eliminate the aperture ring), but since
virtually
all lenses show some light falloff at wide apertures and are
sharper
in the center than the corners, any lens could be considered
"optimized for APS-C" :)
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