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04-10-2011, 05:12 PM   #31
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QuoteOriginally posted by Christine Tham Quote
Have you considered that perhaps there is something wrong with either your camera or lens? Maybe worth getting Pentax to check out.

My K-5 requires minimal or 0 AF fine adjustment for most of my lenses.

And for reference, a friend of mine (non photographer) took this picture - he wanted to try out my camera, and effectively just pressed the shutter button in Green mode.

FA43Ltd: shooting conditions are f1.9 t=1/80 ISO=800 (so EV is approximately 5) in a restaurant with halogen lighting (JPG, no additional processing):


As you can see, her fingers and chin are out of focus, as well as her hair and jacket, but her eyes are focused, so I would say the AF is pretty spot on in that photo.
I guess you are fortunate, Christine. I you can see in my previous post (#20), all of my lenses need significant AF adjustment, ranging between a large negative and a large positive value.

Your sample photo does not indicate the FL used, but at f5.6, it's possible that the DOF may be sufficient to mask a small focusing error if there was one.

04-10-2011, 05:19 PM   #32
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QuoteOriginally posted by bxf Quote
Please judge for yourself.
Pretty girl. are you hers?
Anyway, it's hard to judge the actual light level since you've used flash and haven't included any exif, and you haven't said anything about focus assist, but...
What you have done is hit every parameter that the K5 is known to have problems with.
You are working with lowered tungsten light levels, and you are taking a picture of a red object.
If you were focused on the young woman's skin (which is quite lovely), you have lowered the light levels even more, since black skin is black because it reflects less light.

In short, I'd call it user error at this point, in that you are asking the camera to work properly in a situation that you should know it is going to struggle with.
04-10-2011, 05:22 PM   #33
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QuoteOriginally posted by bxf Quote
Your sample photo does not indicate the FL used, but at f5.6, it's possible that the DOF may be sufficient to mask a small focusing error if there was one.
No, as I mentioned earlier (if you re read my post carefully), the first shot was taken at f1.9 at close range, so I would guess DOF under those conditions would be a few cm (which you can see in the photo - the chin and the ears are starting to get out of focus)

If you are requiring quite large AF adjustments and the pictures are still out of focus, my suggestion is something is probably wrong with the camera.
04-10-2011, 05:37 PM   #34
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QuoteOriginally posted by Class A Quote
...

I don't think the difference you are seeing is caused by Pentax vs non-Pentax lenses. The lens that gives you more inconsistent results is the only really fast lens you have used. I believe that this causes the difference. If you tested an FA 50/1.4 or a DA* 55/1.4, I'm sure you'd see very similar focusing behaviour. Forum user robgo2 tried five (5) DA* 55/1.4 and couldn't find one that didn't focus erratically on his K-7.
Both the Sigma 50mm f1.4 and the Tamron 28-75 focused terribly before I did any AF adjustment, which helped a fair bit in overall AF accuracy. Problem now is inconsistency across different types of lighting. Nevertheless, your point is well taken.

04-10-2011, 05:43 PM   #35
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QuoteOriginally posted by Christine Tham Quote
Here's another example, shot by my friend.

This time, I adjusted the settings to TAv mode f=5.6 t=1/60 (so ISO was calculated at max of 3200 with the camera slightly underexposing)

Again he shot without explicitly focusing or composing, he just pressed the shutter. Mind you, with the above settings, it would have been impossible for the camera to misfocus - I'm just saying that with typical shooting conditions (rather than wide open) there should be no reason why the camera won't do an adequate job so I'm struggling to understand why you are getting the pictures you are posting:
And I can show you some that are much worse These are far from being the least satisfactory. I posted these because for the first time I used the 18-55 in these conditions. Also, I DO get some sharp shots in artificial light, but they are in the minority.
04-10-2011, 05:49 PM   #36
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QuoteOriginally posted by Christine Tham Quote
Here's another example, shot by my friend.

This time, I adjusted the settings to TAv mode f=5.6 t=1/60 (so ISO was calculated at max of 3200 with the camera slightly underexposing)

Again he shot without explicitly focusing or composing, he just pressed the shutter. Mind you, with the above settings, it would have been impossible for the camera to misfocus - I'm just saying that with typical shooting conditions (rather than wide open) there should be no reason why the camera won't do an adequate job so I'm struggling to understand why you are getting the pictures you are posting:
The pictures you are posting are not colour failure pictures, the pictures in question are.
The camera doesn't know, really, when it is pointing at something if the colour of the object is the result of light or fabric dye or skin pigment.
What we do know is that the K5 has problems with red (tungsten light) and dark (black skin tones).
He set the camera up to fail, and it failed.
No surprise there.
04-10-2011, 05:56 PM   #37
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QuoteOriginally posted by Wheatfield Quote
Pretty girl. are you hers?
Totally

QuoteOriginally posted by Wheatfield Quote
Anyway, it's hard to judge the actual light level since you've used flash and haven't included any exif, and you haven't said anything about focus assist, but...
I provided the light levels as shown by PhotoMe. And, it was bright enough for the AF assist to NOT come on.

QuoteOriginally posted by Wheatfield Quote
What you have done is hit every parameter that the K5 is known to have problems with.
You are working with lowered tungsten light levels, and you are taking a picture of a red object.
If you were focused on the young woman's skin (which is quite lovely), you have lowered the light levels even more, since black skin is black because it reflects less light.

In short, I'd call it user error at this point, in that you are asking the camera to work properly in a situation that you should know it is going to struggle with.
Mostly halogen, actually, and not that low - LV as shown previously, range between 6-7, enough for AF Assist to not come on. Results with subject wearing something other than red are no better.

I have bad focus, often worse than shown in these samples, just about any time I shoot in artificial light.
04-10-2011, 06:05 PM   #38
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What precisely were you focusing on?

04-10-2011, 06:09 PM   #39
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QuoteOriginally posted by Christine Tham Quote
No, as I mentioned earlier (if you re read my post carefully), the first shot was taken at f1.9 at close range, so I would guess DOF under those conditions would be a few cm (which you can see in the photo - the chin and the ears are starting to get out of focus)
Yes, sorry Christine. In the absence of the FL I missed the aperture used.

QuoteOriginally posted by Christine Tham Quote
If you are requiring quite large AF adjustments and the pictures are still out of focus, my suggestion is something is probably wrong with the camera.
Well, that's what I'm trying to ascertain, I guess. However, daylight shots are OK in spite of the large adjustment required, so I'm not sure what conclusion to reach at this point.
04-10-2011, 06:11 PM   #40
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QuoteOriginally posted by Wheatfield Quote
The pictures you are posting are not colour failure pictures, the pictures in question are.
The camera doesn't know, really, when it is pointing at something if the colour of the object is the result of light or fabric dye or skin pigment.
What we do know is that the K5 has problems with red (tungsten light) and dark (black skin tones).
He set the camera up to fail, and it failed.
No surprise there.
I guess I should go out and find a wife with different skin colour
04-10-2011, 06:14 PM   #41
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QuoteOriginally posted by Wheatfield Quote
What precisely were you focusing on?
The eyes, though not necessarily always with absolute precision, so any part of the face could have been it.
04-10-2011, 06:18 PM   #42
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QuoteOriginally posted by bxf Quote
I guess I should go out and find a wife with different skin colour
And give up what you have there? Are you daft?
I'd change camera brands before I did that.
But seriously, take a meter reading off one of your white friends and then a reading off your wife and see how different they are. Black skin reflects several stops less light than Caucasian skin if I remember correctly.
This is why I am asking precisely what you were focusing on, since if it was her face, the meter is getting a lot less light to work with than you think it is.
04-10-2011, 07:10 PM   #43
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QuoteOriginally posted by Wheatfield Quote
And give up what you have there? Are you daft?
I'd have to be

QuoteOriginally posted by Wheatfield Quote
But seriously, take a meter reading off one of your white friends and then a reading off your wife and see how different they are. Black skin reflects several stops less light than Caucasian skin if I remember correctly.
This is why I am asking precisely what you were focusing on, since if it was her face, the meter is getting a lot less light to work with than you think it is.
You are correct. I found this out some years back, which is one reason I often use CW metering rather than matrix, which has a greater tendency to underexpose black skin. However, I never thought of it in terms of AF, and that's an interesting point, though I'm not convinced, because she is not darker than many inanimate subjects we shoot without any problems. Still, you may have something there, and I'll have to experiment.
04-10-2011, 07:26 PM   #44
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QuoteOriginally posted by bxf Quote

You are correct. I found this out some years back, which is one reason I often use CW metering rather than matrix, which has a greater tendency to underexpose black skin. However, I never thought of it in terms of AF, and that's an interesting point, though I'm not convinced, because she is not darker than many inanimate subjects we shoot without any problems. Still, you may have something there, and I'll have to experiment.
This may be getting slightly off topic, but also relevant to the topic. Not being a biologist, I don't know the real answer, but some things I have read lead me to believe that the African skin colour is, while percieved as anything from kinda brown to ebony black actually has a lot of reddish brown pigment. I really do wonder if this (if true) isn't what is causing you grief, but not Christine, for example.
IE, it's not just how dark she is, but precisely what colour she is reflecting back to the camera, especially under tungsten light, which is quite red to start with.
If nothing else, this thread has given your wife a fan in Canada.
04-10-2011, 08:10 PM   #45
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QuoteOriginally posted by Wheatfield Quote
This may be getting slightly off topic, but also relevant to the topic. Not being a biologist, I don't know the real answer, but some things I have read lead me to believe that the African skin colour is, while percieved as anything from kinda brown to ebony black actually has a lot of reddish brown pigment. I really do wonder if this (if true) isn't what is causing you grief, but not Christine, for example.
IE, it's not just how dark she is, but precisely what colour she is reflecting back to the camera, especially under tungsten light, which is quite red to start with.
If nothing else, this thread has given your wife a fan in Canada.
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.
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