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02-04-2008, 12:39 AM   #16
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QuoteOriginally posted by m8o Quote
From my recollection the manual explicitly states that the lens 'lines' MTF does work with are only Pentax's own AF lenses, http://www.pentaxslr.com/files/scms_docs//K10D_Manual.pdf >> DA, D FA, FA, or FA J lenses. 3rd party lenses only go so far as supporting the AF mount, not the MTF data protocol (if that's the right way to categorize it).
m8o, that's almost the way the manual for my K10D (p. 145) puts it, but not quite: "MTF priority program is a Program Automatic Exposure that prioritizes the best aperture settings for the attached lens and is most effective when combined with a DA, D FA, FA, or FA J lens." [emphasis added]

That can be read, I think, to suggest that modern, chip-enhanced auto focus lenses from other manufacturers might provide more than just AF data through the KAF or KAF2 (whenever that happens!) mount. If your modern Sigma, Tamron or other chipped AF lens has MTF data to share, it's my interpretation of the manual's wording that the MTF program line setting will try to make use of the data; it's just going to work better when fed by a recent Pentax lens, as it well should!

02-04-2008, 08:13 AM   #17
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Granted, "most effective" is stated in the manual. It's like this...

I was hoping a $3500 (USD) list lens would at least have MTF data in it for the mount being used. The Sigma rep I was dealing with who set my deal up for my 'Biggerma' lens explained to me however that they don't have the MTF data programmed into the lens; nor does any 3rd party mfgr. (else maybe they'd need to do it too )

Regarding the 'less effective' use of it... I don't know if it was supposition on others parts or based on actual testing with 3rd party lenses, but as explained to me the camera makes an 'assumption' of where the lens would operate best. If you look @ MTF charts of a lens that's f/2.8 - f/22 [or f/32], generalizing, they're similar to a bell shaped curve with a bias to the left of center, usually maxing around f/5.6 - f/8 for a f/2.8 lens (only my Voigtlander is near max rez wide open otherwise generally not, and most all lenses fall victim to diffraction at small apertures). So if using a non-Pentax lens if you have enough light, the MTF would use near f/8 if it can, if you don't it would use near f/5.6 if it can or will go lower if it has to. Hope I'm not repeating dis-information here.
02-04-2008, 02:16 PM   #18
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QuoteOriginally posted by m8o Quote
Granted, "most effective" is stated in the manual. It's like this...

I was hoping a $3500 (USD) list lens would at least have MTF data in it for the mount being used. The Sigma rep I was dealing with who set my deal up for my 'Biggerma' lens explained to me however that they don't have the MTF data programmed into the lens; nor does any 3rd party mfgr. (else maybe they'd need to do it too )

Regarding the 'less effective' use of it... I don't know if it was supposition on others parts or based on actual testing with 3rd party lenses, but as explained to me the camera makes an 'assumption' of where the lens would operate best. If you look @ MTF charts of a lens that's f/2.8 - f/22 [or f/32], generalizing, they're similar to a bell shaped curve with a bias to the left of center, usually maxing around f/5.6 - f/8 for a f/2.8 lens (only my Voigtlander is near max rez wide open otherwise generally not, and most all lenses fall victim to diffraction at small apertures). So if using a non-Pentax lens if you have enough light, the MTF would use near f/8 if it can, if you don't it would use near f/5.6 if it can or will go lower if it has to. Hope I'm not repeating dis-information here.
My DA* 16-50 seems to hug f/4 - f/5.6 when set to MTF program line at 16mm. It holds f/4 to 0.3" before shifting to 2.8.

Those of us old enough to remember Modern Photography's lens tests will realize that the MTF program line tries to hold the Pentax lens to the f/stops that produce the highest resolution.
02-05-2008, 08:55 PM   #19
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I've left my camera in the MTF mode, and then attatched an older sigma 28-80 AF zoom, and it metered with multi-segment but I doubt it was using the MTF data from the lens to pick an aperture. The lens will work just fine, but having a pentax lens will give it just that little extra bias in exposure settings.

02-08-2008, 11:03 AM   #20
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MTF and Third party lens

[QUOTE]How does MTF work if I use a non-Pentax lens? Does it revert to Normal program line or something like that?Will[QUOTE]

I set up my K10 this AM and checked a shot from the DA* 50-135 with the Program line set to normal. It wanted to shoot at 1/60 th F2.8. With the Program line set at MTF, it wanted 1/30 F 4.0.

I then tried the same with the Sigma 10-20 and the Normal was 1/15 F 4.0 with the MTF 1/10 F 5.6.

My conclusion is that with the newer third party lenses (Sigma anyway) the MTF function appears to work. Does it give a better image?, further testing required.
02-08-2008, 02:42 PM   #21
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Hi Will

I prefer the definition "Mean Transfer Function". It's that disdainful expression you receive from the counter clerk at the bank when you attempt to withdraw sufficient funds from your bank account in order to indulge in another round of LBA, only to be informed that you are in negative equity YET AGAIN !!!!

Best regards
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02-08-2008, 08:01 PM   #22
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QuoteOriginally posted by WMBP Quote
One of the things I wish for in Pentax's next camera is a more informative user guide!
It would probably be ok already if one english-speaking Pentax engineer would participate in this forum
02-17-2008, 08:17 AM   #23
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[QUOTE=BrianK;173482][QUOTE]How does MTF work if I use a non-Pentax lens? Does it revert to Normal program line or something like that?Will
QuoteQuote:

I set up my K10 this AM and checked a shot from the DA* 50-135 with the Program line set to normal. It wanted to shoot at 1/60 th F2.8. With the Program line set at MTF, it wanted 1/30 F 4.0.

I then tried the same with the Sigma 10-20 and the Normal was 1/15 F 4.0 with the MTF 1/10 F 5.6.

My conclusion is that with the newer third party lenses (Sigma anyway) the MTF function appears to work. Does it give a better image?, further testing required.
OK, curiosity finally got to me on this topic. I just now took my K10D with a Sigma 17-70 on it and tried it. In a dimly lit room, the first exposure reading with the program set to normal was a 2.8 aperture. I switched the program line to MTF and took the same angle, same location, same light, (15 seconds later) exposure reading and it was at f:4.0. Conclusion, MTF did make a change. Is it to the lens' best aperture or just away from extreme open? No way to tell (without extensive, subjective testing).
Brian

02-17-2008, 11:09 AM   #24
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QuoteOriginally posted by calicojack Quote
Is it to the lens' best aperture or just away from extreme open? No way to tell (without extensive, subjective testing).
An answer to that possibly is if other lenses of the similar focal range and speed from Tamron and Tokina (if they were to exist) were to get the same aperture selected for them at the same focal length (tho I guess that's what you mean by extensive testing). I stand by that Pentax has tables for their lenses that MTF mode follows, and a default table is used for 3rd party lenses and that none of them operate 'optimally' for that particular lens in MTF mode.
02-20-2008, 03:20 PM   #25
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But Is It Useful?

I've always thought MTF was a cool program line--especially since LBA loaded my kit with extreme glass...But from PZ1 to PZ1p to MZS to K100D and now K10D, I've had MTF capability for 15 years and never bothered to use it. Always needed a particular speed or aperature and never let program have the choice. Does anyone actually shoot MTF program line? And if so, under what circumstances? Is it better to choose the "sweet spot" from technical data and resolution charts? Or will the MTF line find it for you? Does MTF find the very sharpest aperture or an aperture that's sharper than standard program but not always the very sharpest? I ask this because the examples people are citing tend toward one stop closer to the sweet spot than standard program, but I can't believe all those lenses are their very sharpest at those f. 4 type apertures as listed. And lastly, without a Pentax engineer stepping in, or someone documenting lens resolution figures...are we all just guessing about how MTF works?
02-20-2008, 03:30 PM   #26
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QuoteOriginally posted by Ron Boggs Quote
...I've had MTF capability for 15 years and never bothered to use it. Always needed a particular speed or aperature and never let program have the choice. Does anyone actually shoot MTF program line?
MTF sounds good on paper, but I never use it, and to be honest, when I say it "sounds good," I only mean that it sounded neat the first time I heard about it, but after thinking about it more and more, I just don't see the point. Like you, I generally have a reason to set the aperture where it's getting set. On my own, I will try to avoid the extreme ends of any zoom when I can, both the extremes of focal length and the extremes of aperture.

I generally keep my K10D's preferred program line set to aperture priority or program line. Seems to work okay.

Will
02-20-2008, 03:38 PM   #27
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I suspect that even without a MTF chip that the camera can make certain assumptions. Don't shoot wide open unless you have to is one those constants. 1-2 stops down seems to give better performance on nearly every lens, and you want to avoid extemely small apertures as well.
02-25-2008, 03:21 PM   #28
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I use only Sigma lenses and the MTF line works with each of them. If your third party lens fits the Pentax specs it will work.

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02-25-2008, 09:40 PM   #29
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to test this further, wouldn't you be able to point the camera at something that's rather bright to give a aperture like f16 or f22 (if lens supports) then the MTF program should try to open that up a bit (smaller f number) and increase the shutter speed to match to get nearer the lenses sweet spot.
02-25-2008, 11:24 PM   #30
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QuoteOriginally posted by HGMonaro Quote
to test this further, wouldn't you be able to point the camera at something that's rather bright to give a aperture like f16 or f22 (if lens supports) then the MTF program should try to open that up a bit (smaller f number) and increase the shutter speed to match to get nearer the lenses sweet spot.
If you set your program line to MTF, the camera will attempt to maintain the sweet spot apertures, and adjust the shutter speed to compensate - or even adjust the ISO in the proper modes.
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