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05-31-2013, 10:39 AM   #1
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Pentax Lens Performance

Does anyone have a sense of how the DA* lenses will perform on the full frame body when it is released? They've always been billed as Pentax's response to the DSLR, which has implicitly meant a cropped frame. I expect my DA* 15-60mm will now perform at it's true focal length. But, I'm wondering how much f-stop I'll lose if I convert from my K-5 to FF.

Am I correct to think that f2.8 will perform at about f3.5? And do folks expect vignetting, since the DA* line was built to hit a smaller target than the full frame?

Finally, will the SMC Pentax-FA Ltd. lenses maintain their f-stops on the full frame? I feel more confident that because the FA series was designed for film, there will not be any vignetting or performance drop off on a FF body.

05-31-2013, 10:51 AM   #2
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It depends on which lenses we're talking about. The 16-50 does not cover the so-called FF format; other lenses, like the 200 and 300mm primes, should do.

One thing, though: a lens' focal length does not depend on the camera. Let me rephrase that: the focal length is an exclusive property of the lens, and it remains the same no matter if it's mounted on a camera or not, no matter on which camera you'll put it on, no matter how much you will crop the image afterwards. The aperture is also a characteristic exclusive to the lens, and will remain the same.
05-31-2013, 10:52 AM   #3
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I believe only the DA*60-250 and the primes will even cover the full frame image circle, vignetting in the extreme. The properties of the lenses will not change. The aperture is aperture. The FA LTDs will feel right at home on a full frame body.
05-31-2013, 11:00 AM   #4
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focal length is a property of the lens. They always perform at their "true" focal length. Same thing with aperture. It is a property of the lens.
The format of the sensor used is another thing. Be it FF, APS-C, 1/2.3 (Q sensor). Depending on the sensor used you will have:
Different field of view (for the same focal length);
Different depth of field (for the same aperture value);

05-31-2013, 11:22 AM   #5
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The DA *55, 200, and 300 all should be fine on full frame. 60-250 is probably passable stopped down a little, but weak wide open (although the patent says it is full frame compatible).
05-31-2013, 11:29 AM   #6
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QuoteOriginally posted by MCSpitz Quote
Am I correct to think that f2.8 will perform at about f3.5? And do folks expect vignetting, since the DA* line was built to hit a smaller target than the full frame?

Finally, will the SMC Pentax-FA Ltd. lenses maintain their f-stops on the full frame? I feel more confident that because the FA series was designed for film, there will not be any vignetting or performance drop off on a FF body.
The aperture does not change, going from a smaller sensor to a larger sensor. It just means the larger sensor "sees" more of the image circle cast by the lens.
05-31-2013, 01:06 PM   #7
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I am amazed the $7,000 DA 560mm F5.6 is not a full frame lens.
DA 560mm F5.6 - is it a Full-frame lens? - Photographic Articles - PentaxForums.com
Format Compatibility Pentax Digital (APS-C) :
Pentax DA 560mm f/5.6 ED AW Lens 22180 B&H Photo Video
That is bad news for anyone waiting for a full frame Pentax DSLR IMHO.
05-31-2013, 02:18 PM   #8
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Are we sure it isn't? IIRC Pentaxforums backpedalled on their initial assertion, and for good reason: some high end "full frame" Canikon lenses vignettes equally as bad.
Of course, that article should have been corrected but it wasn't. Sloppy.

05-31-2013, 04:50 PM   #9
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QuoteOriginally posted by Kunzite Quote
Of course, that article should have been corrected but it wasn't. Sloppy.
Agreed. I'll post this here as well as the other thread where this got raised: even $10,000+ Sony/Zeiss and Canon telephotos vignette heavily on full-frame. Some people should know better than to spread such FUD.

05-31-2013, 05:00 PM   #10
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QuoteOriginally posted by MCSpitz Quote
Does anyone have a sense of how the DA* lenses will perform on the full frame body when it is released?
They will probably perform fine if the Pentax full-frame has the option - like the Nikon D800 or D600 for example - to switch the camera to APS-C mode when using DX lenses or just for crop reach. It may not be useful for permanent shooting, but it would allow direct use of DA lenses like the 16-50 on the Pentax FF body whenever needed.
06-01-2013, 01:38 PM   #11
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QuoteOriginally posted by rawr Quote
They will probably perform fine if the Pentax full-frame has the option - like the Nikon D800 or D600 for example - to switch the camera to APS-C mode when using DX lenses or just for crop reach. It may not be useful for permanent shooting, but it would allow direct use of DA lenses like the 16-50 on the Pentax FF body whenever needed.
Functionally isn't this equivalent to a digital crop later? I guess you could save on disk space. Theoretically it also seems like you could do SR purely on-sensor, just move a "window" across the sensor instead of moving the whole sensor.
06-01-2013, 02:25 PM   #12
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QuoteOriginally posted by Paul MaudDib Quote
Theoretically it also seems like you could do SR purely on-sensor, just move a "window" across the sensor instead of moving the whole sensor.
This probably only works for video (and I think K-01 and K-30 already do this for video), or if each photo is made out of several captures. FI a image with 1/50 s shutter speed is made out of 10x 1/500 s images where pixels are aligned between each shot.
06-01-2013, 02:49 PM   #13
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Yes, it's just cropping - and (I'll have to check the DNG specifications on that) it could even be implemented as a simple marker, leaving the data intact, or by discarding the "useless" borders..
That kind of SR can't work, except as a series of multiple, fast exposures; because there's no "window" to be moved during the exposure, only before/after it.
06-01-2013, 04:48 PM   #14
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QuoteQuote:
The format of the sensor used is another thing. Be it FF, APS-C, 1/2.3 (Q sensor). Depending on the sensor used you will have:
Different field of view (for the same focal length);
Different depth of field (for the same aperture value);
FYI, DOF does not change, as it is a factor of focus distance and aperture for a given focal length. The sensor size is not a factor. The area of sharpness/focus may appear larger merely because it covers a larger portion of a smaller sensor. Actual DOF in relation to the scene/subject is not significantly influenced.

You can get down deep into into pixel size for different sensors and circles of confusion and their effect on DOF and perceived sharpness, but I haven't found that to play a significant role in real life. YMMV.
06-01-2013, 04:56 PM   #15
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QuoteOriginally posted by amoringello Quote
FYI, DOF does not change, as it is a factor of focus distance and aperture for a given focal length. The sensor size is not a factor. The area of sharpness/focus may appear larger merely because it covers a larger portion of a smaller sensor. Actual DOF in relation to the scene/subject is not significantly influenced.

You can get down deep into into pixel size for different sensors and circles of confusion and their effect on DOF and perceived sharpness, but I haven't found that to play a significant role in real life. YMMV.
Careful now. You are treading on the number two reason for the Holy Full Frame according to PentaxForums...after "I want to use my old lenses" of course.

Last edited by boriscleto; 06-01-2013 at 05:26 PM.
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