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Author Topic: Mamiya lens comparisons, 645 vs RZ 67 series  (Read 3033 times)
ErikKaffehr
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« Reply #20 on: October 18, 2012, 04:21:58 PM »
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Hi,

Thanks for positive feedback. I would just add two points.

1) The issue with the four backs was described by Joseph Holmes and the person involved was Mark Dubovoy. Mark is said to shoot often with large apertures. He is also an old 8x10" shooter so I think he is very persnickety with sharpness.

2) The other issue is that you clearly say that if there is a problem it can be solved by a good dealer. That is a very good reason to work with a good dealer (like CI).

Best regards
Erik


Agreed with most of what you're saying here Erik, with the emphasis on - test new equipment thoroughly and return for exchange or resolution promptly. With existing equipment - let's say you've shot with a digital back on your camera system for 2 years and you've noticed lately the viewfinder focus point and the resulting image focus point don't seem to agree -  then don't allow this to remain un-resolved. It is resolvable. It's only a problem and there is a solution.

There is 1 situation where 4 different backs on the same body with 2 in focus and 2 out of focus are not the digital back, and that is when it comes to what is behind the camera/digital back. But assuming that is good as well, then simply get it resolved.

If someone took every camera and lens combination - and precisely tested the focusing accuracy for each, a larger percentage would show as not being in proper calibration/alignment than is reported. There are some who are not aware they are not within the stated tolerances due to the nature of how they use the product, or the difference is not great enough for them to notice.

But I have never ever had any situation where the focus tolerances could not be resolved satisfactorily.


Steve Hendrix
Capture Integration
« Last Edit: October 18, 2012, 04:23:56 PM by ErikKaffehr » Logged

ondebanks
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« Reply #21 on: October 22, 2012, 10:49:01 AM »
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you may find my brief tests useful: -

http://www.tonyhowell.co.uk/lenstests.htm

The 35mm lens is bad!

Nice to see your tests, Tony. But the 35mm is not there?

Ray
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ondebanks
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« Reply #22 on: October 22, 2012, 10:58:22 AM »
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I had a 24mm fisheye and it was not very sharp even on 28MP (found it as new stock as late as ca. 2007). Same was for my copy of 35mm AF, though there is also a newer AF D? version of it which should be better.

Anders, you're the first person I've come across who didn't find the 24mm fisheye outstanding. My sample certainly is, even wide open. You must have had bad luck!

Re. the 35mm: the C, N and AF versions are all the same optical formula, bar tweaks to the multicoatings. The AF D version is probably different - I haven't seen that design in detail.

The C/N/AF version has pronounced field curvature. Many people notice this in part of their images and say "I got a bad sample". But if they conduct a careful test and the effect is radially symmetric, then it's just the design, not a particular bad copy. BTW stopping down reduces the impact of field curvature.

Ray
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ErikKaffehr
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« Reply #23 on: October 22, 2012, 11:38:37 PM »
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Hi,

Just a few questions on field curvature.

1) My take is that if it makes for unsharp corners or even edges in landscape shooting (where we often shoot at infinity) it is a bad thing. Correct?

2) If we stop down sufficiently, depth of focus will cover up field curvature, so we can live with it?

3) If we need to stop down to much we loose central sharpness due to diffraction, but that can be compensated to some degree with sharpening.

I'm very much interested to hear your take on the issue.

Best regards
Erik



The C/N/AF version has pronounced field curvature. Many people notice this in part of their images and say "I got a bad sample". But if they conduct a careful test and the effect is radially symmetric, then it's just the design, not a particular bad copy. BTW stopping down reduces the impact of field curvature.

Ray
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ondebanks
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« Reply #24 on: October 24, 2012, 10:23:25 AM »
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Hi,

Just a few questions on field curvature.

1) My take is that if it makes for unsharp corners or even edges in landscape shooting (where we often shoot at infinity) it is a bad thing. Correct?

2) If we stop down sufficiently, depth of focus will cover up field curvature, so we can live with it?

3) If we need to stop down to much we loose central sharpness due to diffraction, but that can be compensated to some degree with sharpening.

I'm very much interested to hear your take on the issue.

Best regards
Erik



Hi Erik,

Basically - yes; yes; and yes.

It is disconcerting to follow the plane surface of sharp focus in an image taken with the 35mm wide open. You can do this if you have fine detail (like long grasses) from right at your feet out to a long distance, and you focus at infinity where you have say, a line of leafless trees. In the centre of the frame, it's really crisp at infinity; then the trail of sharpness sweeps closer as you scan the image to the left and right. At the edges it may be only around 10 feet from where you set up the camera. It's sort of...parabolic.

Ray
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