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04-10-2011, 08:35 PM   #46
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QuoteOriginally posted by bxf Quote
Interesting theory, though I would have guessed that Caucasian skin also has a fair bit of red content. Not sure if this is related, but I do often find myself often cutting back the red in post in order to achieve the skin colour I prefer and which looks more realistic to my eyes. I'll have to find some shots taken under this light where I didn't focus on the skin and see if your suggestion has merit.
Lots of red content, but also several stops more reflectivity, at some point there is enough light for the AF problem to go away in all but more extreme conditions.

04-11-2011, 02:19 AM   #47
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QuoteOriginally posted by bxf Quote
Please judge for yourself.
I think the red dress is confusing the AF sensors, could you please repeat without it?

QuoteOriginally posted by bxf Quote
I guess I should go out and find a wife with different skin colour
We can swap wifes, K-5 can focus fine on the white skin of my wife
04-11-2011, 04:24 AM   #48
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QuoteOriginally posted by bxf Quote
Please judge for yourself.

I usually prefer to use my 28-75mm Tamron for this type of shooting, but here I switched to the 18-55WR, just to see if the focusing is any better. AF adjustment is set to -7, though my tests with this lens indicate that -9 is optimal at 35 & 55mm, and around +5 at 18mm. I'd say that this lens is focusing better than the Tamron (which was terrible before I did some AF adjustment and which prompted my looking into this AF problem), but the wider FL and smaller aperture may be responsible for the apparent improvement. Flash was (mostly) bounced off the corner of the ceiling behind me. Please do not comment on the lack of artistic merit here - these are just snapshots, and no effort at all has gone into making these examples of good portraiture. ISO is 1600, SR ON.

The following are JPEGs saved directly from the DNGs (using Faststone Image Viewer 4.4), with no processing at all. Light was a combination of mostly halogen with a bit of tungsten. Light level value in each file name is the Effective LV from PhotoMe, though the individual AE matrix segments are shown as always being lower than the Effective LV (I don't understand this). Metering is CW.

I would have supposed that some of the softness is due to lens limitations (and perhaps even some camera or subject movement?), but nevertheless, it seems to me that the focus is neither accurate not consistent, but perhaps I'm expecting to much from some of my lenses. Your comments about whether or not the lens is soft, is in proper focus, and if not, where it's actually focusing (i.e. FF or BF) would be appreciated. I do realize that, in the absence of any foreground, not all the shots here make it possible to determine the actual point of focus, though I selected some photos specifically because they DO show some foregroung and background.

Once again, thanks for any input.

Edit: I thought the file names would show up and provide appropriate info. Here it is (left to right, top to bottom):

55m F5.6 1/90 LV7.8
23mm F4 1/60 LV5.9
23mm F4 1/60 LV5.9
35mm F4.5 1/60 LV6
37mm F4.5 1/60 LV6
if your shooting Raw..then you will have to post process and sharpen the image..as Jpegs taken with the camera are sharpened .. whilst Raw {DNG's} are not

if i was you Id have a go at shooting Jpeg and raw together, then compare each file untouched..and see if there is a improvement


EDIT

Ive just tried my own advice..the raw files shot with my D300s are as sharp as the Jpegs ..so perhaps Ignore my advice !!

Last edited by Tommot1965; 04-11-2011 at 04:43 AM.
04-11-2011, 04:35 AM   #49
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QuoteOriginally posted by Class A Quote
...
I think this is a pretty wild speculation. It would mean that Pentax cameras discriminate third-party lenses (I know that in-camera lens corrections only work for Pentax lenses but this is a different matter). This would be a serious detractor for buying Pentax cameras, AFAIC. Pentax needs the third-party lens manufacturers to offer their customers a reasonable set of lenses to choose from.
...
Just speculation ... the point being that if there are lens traits taken into account in the design of the AF system they are likely to be Pentax lens traits. I'm not saying this would be something designed to hurt 3rd parties rather an expression of an attitude where 3rd party lenses are not either discouraged or encouraged as would seem to be the case.

The speculation about chromatic aberrations is based on K-5 AF apparently being sensitive to the color/spectrum of light, and BF/FF in general being lens/copy specific. In general, I suppose (consistent) AF failure is about the AF sensor seeing a different image than the image sensor sees. If one looks at the light path for something that might cause this the AF optics are an obvious suspect.

The point of the speculation, I guess, would be sparking discussion which in the ideal case has results of pragmatic merit, and, failing that, at least intellectual interest. Failing both, we at least have a social thing going . Failing even that, at least someone looking for thesis material in sociology/psychology/... might benefit ).

04-11-2011, 05:37 AM   #50
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QuoteOriginally posted by simico Quote
I think the red dress is confusing the AF sensors, could you please repeat without it?
Sure, no problem, please see new attachments, and perhaps somebody can explain to me how the first (f4, 1/125), taken with AF adjustment of -7, can be so OOF, AND have blurred background (implying no BF), yet the second (f4, 1/90), taken with AF adjustment of -3 (i.e. less backwards adjustment), is sharp? (Tamron 28-75 f2.8)

I just had another look at these images, and I recalled that the first was shot under tungsten only, and for the second I turned on a fairly strong halogen lamp, which takes me back to my original point: AF seems to behave differently under different lighting, not necessarily directly related to low light only.

QuoteOriginally posted by simico Quote

We can swap wifes, K-5 can focus fine on the white skin of my wife
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04-11-2011, 05:39 AM   #51
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QuoteOriginally posted by Tommot1965 Quote
if your shooting Raw..then you will have to post process and sharpen the image..as Jpegs taken with the camera are sharpened .. whilst Raw {DNG's} are not

if i was you Id have a go at shooting Jpeg and raw together, then compare each file untouched..and see if there is a improvement


EDIT

Ive just tried my own advice..the raw files shot with my D300s are as sharp as the Jpegs ..so perhaps Ignore my advice !!
Well, your original comment would be correct, depending on the level of in-camera sharpening you select for your JPEGs. But I've already taken this into consideration.
04-11-2011, 05:53 AM   #52
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QuoteOriginally posted by bxf Quote
Well, your original comment would be correct, depending on the level of in-camera sharpening you select for your JPEGs. But I've already taken this into consideration.
cool

I got shot of my K5 due to problematic Af....it would focus perfectly in low light with a screw drive Prime...but no good with two of motor driven lenses..on a HSM and the other a SDM....it was something I could no longer put up with so I returned it along with the originally lens I bought..

it would however focus fine from 40mm onwards with any lens...crazy..from 40 mm down it was perfect with Live view..but phase detect was a issue...my new body has no such issues {not a k5}
04-12-2011, 11:22 PM   #53
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Hi Friends
I would like to contribute my two cents worth. Because I do not appear to have a problem with AF I decided to do a simple (unscientific) test, not to start an argument here, but to satisfy my own curiosity on the matter of failing focus under red light conditions.

The Metz 58 AF-1 as a lot of you know has its own focus assist light and unlike its Pentax counterpart it is red. Also when the Metz is switched on Pentax turns its green assist light function off.

So I went into a dark room (very dark) and let the K-5 find its focus provided by the red Metz light only. Then I took the same shot with the lights on in the room (to help me focus), manually focused (I have the Katz Eye installed) and took a shot also with the same flash gun. In between all these shots I reset the focus to infinity, particularly in the AF test so Pentax's focus function had a good chance to show its wares. You can inspect the sample pics below. Shot in RAW format and totally untouched in PP. The lens: Tamron SP 24-135.

I'll be interested to hear your your opinion.


Last edited by Schraubstock; 07-24-2011 at 11:38 PM.
04-13-2011, 03:59 AM   #54
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QuoteOriginally posted by Schraubstock Quote

The Metz 58 AF-1 as a lot of you know has its own focus assist light and unlike its Pentax counterpart it is red. Also when the Metz is switched on Pentax turns its green assist light function off.
Just FYI, the Pentax 540 flash is the same: red assist light, and the green BODY light is inactive when the FLASH assist light is used. For what it's worth, the light in MY shots was bright enough for the assist light to not come on.

I don't see a significant difference between your two shots, particularly with respect to focus accuracy. The first appears to have slightly more contrast, but that could be due to the different exposures that would be required according presence or absence of the room lights.

I hope I'm seeing things correctly, as my eyes are not what they used to be

By the way, I like your dark room, and I'm curious about that high tech device on the lower left
04-13-2011, 06:14 AM   #55
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QuoteOriginally posted by bxf Quote
By the way, I like your dark room, and I'm curious about that high tech device on the lower left
It's a mains toilet flusher.
04-13-2011, 06:59 AM   #56
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Sinne pönttöön vain ja huuhtelee alas.
04-13-2011, 09:35 AM   #57
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QuoteOriginally posted by 30v iPentax Quote
Sinne pönttöön vain ja huuhtelee alas.
Oh, I didn't know there was audio with the photos
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