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03-17-2012, 09:48 PM   #1
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Comprehensive Testing: Results & Observations with Pentax 645 Lenses used on the 645D

Hi All,

In case you are interested, I just posted my comprehensive review of multiple samples of most all Pentax FA AF 645 single focal length lenses (and a few FA zooms) when used on the 645D. The link is to my comprehensive 645 lens test is:

http://forum.getdpi.com/forum/medium-format-systems-digital-backs/35577-comprehensive-testing-results-observations-pentax-645-lenses-used-645d.html

Thanks!

Dave (DandA)

03-18-2012, 05:02 AM   #2
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Why did you use AF? Then you are also testing the AF systems accuracy. No AF system will focus at the lens optimum performance, except by luck, as the precision of any AF system is way below the lens/camera optimal resolution. Ie any AF system will say that the image is in focus at a ballpark figure; AF sensors cannot resolve as much as the lenses....
03-18-2012, 08:46 AM   #3
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QuoteOriginally posted by Pål Jensen Quote
Why did you use AF? Then you are also testing the AF systems accuracy. No AF system will focus at the lens optimum performance, except by luck, as the precision of any AF system is way below the lens/camera optimal resolution. Ie any AF system will say that the image is in focus at a ballpark figure; AF sensors cannot resolve as much as the lenses....
And yet people use AF systems all the time resulting in sharp images...
03-18-2012, 12:13 PM   #4
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Dave: Thank you so much for the tremendous amount of work obviously put in to this. I have printed this out, and it will become my "Bible" for 645D lenses!
Again....thanks
Dave in NJ

03-18-2012, 12:46 PM   #5
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In your test of the FA 35, you say spherical curvature. What I think you mean is that it is the aberration called field curvature, where the image is not flat on the focal plane but curved to some extent.
03-18-2012, 10:50 PM   #6
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Hi All,

Permit me to address some of your questions. First good to see you Pal (I'm Zx5Lx from the old Pentax Discussion Group days!). There are many ways to conduct tests such as these and I certainly could have strictly used MF. Unlike a35mm DSLR or film SLR that has a good fresnel or split image focusing screen, the stock 645D does not , and so focusing accuracy would not be precise enough or repeatable. There was just as much chance for user error as with the AF system. Keep in mind I was also testing for best Af fine tune setting with the 645D. I repeated each and every test on each lens multiple times and along with testing all the various Af fine tune settings (with each lens)...one can be almost certain I would find the optimal focus point for max. sharpness.

When I mentioned spherical curvature I did mean field curvature. Although spherical curvature may not be the most accurate term, many use it interchangeably with the term field curvature and in fact in detailed iscussions with a few optical lens designers, they more often used the phrase for what I described.

Anyhow, I'm glad you asked so that I could clarify.

Dave (in N.J.), as you know I responded to your extremely kind words over on the other forum. I always enjoy running across and reading your postings. Thanks again.

Dave (DandA)
03-19-2012, 08:37 AM   #7
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great work, thanks, Dave!
03-19-2012, 09:48 PM   #8
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Your're welcome phonoline. It's all about sharing information with fellow shooters, especially those that use similar equipment. I know I've often been extremely greatful to those who went the extra mile and helped me out, especially with their tests and recommendations, which saved both time and money.
I've also found Pentax shooters in particular are always pasionate and enthusiastic and welcome varying opinions.

Dave (D&A)

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