I think it is more involved than just field curvature. I posted this
link quite awhile ago
http://www.16-9.net/lens_tests/15mm_2/sigma1224vnikon15f.html
Initial testing made the N*kon 15/3.5 look pretty poor on the C*non.
By changing to a thicker adapter, the N*kon was found to do very well.
Probably any lens which has a close focusing group that moves
separately form the other elements could be very sensitive to the
register distance.
The four OM adapters that I've tried on my 5D seem to be very close to
the same thickness but I'm seeing some repeatability problems. I've
mounted a couple lenses that seem to have had infinity focus way off
but when I come back a couple days later to test/compare I'm not
seeing the origninal problem.
For what it's worth the cheap $20 chinese adapter (using an easily
visible screw to stop down the lens) and the cameraquest adapter seem
to have very similar thickness. The mid-priced adapter I got from
Martin Cheung(?) is junk. The lens rocks back and forth on the mount.
A recent adapter advertised as a high quality Japanese adapter ($86)
appears to be assembled wrong preventing the lens from mounting
correctly but seems to be very close to the thickness of the $20
adapter & the cameraquest adapter. The cameraquest adapter was loaned
to me recently by Mike. I've only had it available to me for the last
24 hours so I need to do some more testing.
-jeff
On 9/26/06, Moose <olymoose@xxxxxxxxx> wrote:
> Doesn't seem so odd to me. Non-macro lenses from the MF era will
> generally have noticeable field curvature. And it becomes more of an
> issue at closer focal distances. There were some sample images from a
> 21/3.5 posted here a few years ago that showed a great deal of it in the
> 21/3.5 used close-up.
>
> This is just the thing addressed by the Minolta 24 mm VFC lens discussed
> here in the last few days.
>
> A practical solution is to use the matte area to check center and edge
> focus of parts of the image that should be in focus and pick something
> in between. That way, your DOF is used to best advantage.
>
> Moose
> Paul Martinez wrote:
> > I've found the Zuiko 28/2.8 to be the worst of the Zuiko 28's. I've tried
> > them all on my FF Kodak SLR/c and found the /2 and /3.5 to be much better.
> > Also, becuase many Zuiko's are old and out of adjustment, no solid
> > conclusion should be made from a single sample. A good performing Zuiko 28/2
> > will blow away any zoom lens on a FF DSLR in the corners, even at f/8.
> >
> > Other things also need to be considered, like the adapter you used and how
> > you focused. The 28mm primes (including the Zeiss and Leica's) are very
> > picky about what adapter you use on them. A poorly matched adapter will give
> > poor results. It is often not as critical on a zoom lens at 28mm because
> > they are much steeper retro-focus design at 28mm. For focus stopped down,
> > leaning much more than you would think resonable to the infinity mark will
> > give much better corner performance and DOF. Odd, but true.
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