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12-17-2014, 12:26 PM   #1
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Focus unaccuracy

I've been testing the K-5 II, trying to get the 35 to focus correctly. I'm getting really frustrated with the focus (in)accuracy of the camera. I'm doing real tests and not using a chart - Christmas tree, kitchen stuff, my baby girl, etc - but it's getting frustrating that it sometimes focusses in front, sometimes behind... I feel like the camera isn't in single point, but in some kind of auto that I can't seem to get to grips with................. I'm starting to wonder if I did good switching...

12-17-2014, 12:36 PM   #2
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QuoteOriginally posted by Flugelbinder Quote
I've been testing the K-5 II, trying to get the 35 to focus correctly. I'm getting really frustrated with the focus (in)accuracy of the camera. I'm doing real tests and not using a chart - Christmas tree, kitchen stuff, my baby girl, etc - but it's getting frustrating that it sometimes focusses in front, sometimes behind... I feel like the camera isn't in single point, but in some kind of auto that I can't seem to get to grips with................. I'm starting to wonder if I did good switching...
An example would be helpful to identify (hopefully) where the problem lies... I have all three, k-5, k-5IIs and k-3 all tuned to take sharp crispy photos at wide-open aperture of my MF 58f1.4 lens.
12-17-2014, 12:43 PM   #3
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QuoteOriginally posted by Flugelbinder Quote
I'm getting really frustrated with the focus (in)accuracy of the camera. I'm doing real tests and not using a chart - Christmas tree, kitchen stuff, my baby girl, etc - but it's getting frustrating that it sometimes focusses in front, sometimes behind...
Where are the focus points for your real world subjects? One of the dirty secrets of AF photography is that the camera does a very poor job of reading our minds or dealing with complex subjects with a fair difference in distance in a small angle of arc. A good example might be an angled portrait where the intent is to focus on the eye, but the focus point locks focus on the leading edge of the cheekbone, the nose, or something in the background. Even with a single focus point there is often a problem with discrimination. This is true regardless of brand or cost of camera.


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12-17-2014, 12:45 PM   #4
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QuoteOriginally posted by Flugelbinder Quote
Christmas tree
BTW...one of the most difficult subjects there is for AF...


Steve

12-17-2014, 12:47 PM   #5
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QuoteOriginally posted by Flugelbinder Quote
I'm doing real tests and not using a chart - Christmas tree, kitchen stuff, my baby girl, etc - but it's getting frustrating that it sometimes focusses in front, sometimes behind...
Sorry, those are not real tests, those are snapshots, which will tell you nothing.

Put the camera on a tripod, get a proper focus target and make sure it is precisely aligned both vertically and horizontally. If that test can produce sharp images then the issue is not with the lens / camera. If this test does not yield sharp images then look into AF fine tuning.

Assuming the test above yields correctly focused images then you need to look to how the AF system is set up and what depth of focus you are using. The AF center point on the k-5II is quite large, generally considered to be the size of the "()" brackets in the view finder. Anything in that space is considered fair game for the AF system and it has no idea whether the child's face or the tree behind is supposed to be in focus.

Post some examples with the EXIF intact, that often helps.
12-17-2014, 12:59 PM   #6
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He is not the only one -- I have been fed up with getting 'back focus' on my 2007 K10D both with the 18-55mm 'kit lens and my Pentax manual focus lenses. At my Camera Club there is only ONE more member who uses Pentax now -- none of the 'other makes' seem to suffer from this focus problem.
12-17-2014, 01:07 PM   #7
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QuoteOriginally posted by pentaxpete Quote
He is not the only one -- I have been fed up with getting 'back focus' on my 2007 K10D both with the 18-55mm 'kit lens and my Pentax manual focus lenses. At my Camera Club there is only ONE more member who uses Pentax now -- none of the 'other makes' seem to suffer from this focus problem.
Simply not true... when the camera gets out of production line, there is certain amount of tolerance allowed during manufacturing QC process. I have friends who had 5D, 6D, D610, D800, they have similar problems... most who said they don't have BF or FF problems are simply just not aware of it as most of them shoot in 'auto' mode.
12-17-2014, 01:09 PM   #8
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QuoteOriginally posted by stevebrot Quote
Where are the focus points for your real world subjects? One of the dirty secrets of AF photography is that the camera does a very poor job of reading our minds or dealing with complex subjects with a fair difference in distance in a small angle of arc. A good example might be an angled portrait where the intent is to focus on the eye, but the focus point locks focus on the leading edge of the cheekbone, the nose, or something in the background. Even with a single focus point there is often a problem with discrimination. This is true regardless of brand or cost of camera.


Steve
On my baby girl is either on the hair/head, or some part of the clothes...

---------- Post added 12-17-14 at 01:10 PM ----------

QuoteOriginally posted by stevebrot Quote
BTW...one of the most difficult subjects there is for AF...


Steve
I know, that's why I'm stressing the af, to get some real results.

12-17-2014, 01:10 PM   #9
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QuoteOriginally posted by Flugelbinder Quote
I've been testing the K-5 II, trying to get the 35 to focus correctly. I'm getting really frustrated with the focus (in)accuracy of the camera. I'm doing real tests and not using a chart - Christmas tree, kitchen stuff, my baby girl, etc - but it's getting frustrating that it sometimes focusses in front, sometimes behind... I feel like the camera isn't in single point, but in some kind of auto that I can't seem to get to grips with................. I'm starting to wonder if I did good switching...
The simplest test you can do is to line up 3 AA batteries; shoot and focus in the middle one at a 45 degree angle, using center focus point. If the photo shows the AA battery in front is sharper than the middle one, you have a FF problem, the opposite is true if the battery in the rear is sharper than the middle, you have a BF problem.
12-17-2014, 01:11 PM   #10
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I just got one of these a few days ago to help tune the focus on my lenses: LensAlign

If it were only a pentax problem, it would probably not exist.

Perhaps the other people in your camera club just aren't paying close attention... or they're using slower lenses that have a wider depth of field that will hide minor front or back focusing... or they may have inferior cameras that don't allow AF fine tuning in the first place... or they're like most people who barely use the expensive cameras they own, working very hard to justify how much money they spent by talking about how great it is and how it never gives them any problems at all.
12-17-2014, 01:14 PM   #11
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QuoteOriginally posted by jatrax Quote
Sorry, those are not real tests, those are snapshots, which will tell you nothing.

Put the camera on a tripod, get a proper focus target and make sure it is precisely aligned both vertically and horizontally. If that test can produce sharp images then the issue is not with the lens / camera. If this test does not yield sharp images then look into AF fine tuning.

Assuming the test above yields correctly focused images then you need to look to how the AF system is set up and what depth of focus you are using. The AF center point on the k-5II is quite large, generally considered to be the size of the "()" brackets in the view finder. Anything in that space is considered fair game for the AF system and it has no idea whether the child's face or the tree behind is supposed to be in focus.

Post some examples with the EXIF intact, that often helps.
I have nothing but respect for your insights - for what I've been able to read here - but that kind of comments, without you knowing my skills, are just......
12-17-2014, 01:14 PM   #12
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QuoteOriginally posted by Flugelbinder Quote
On my baby girl is either on the hair/head, or some part of the clothes...

---------- Post added 12-17-14 at 01:10 PM ----------



I know, that's why I'm stressing the af, to get some real results.
But a christmas tree is not a flat surface. the auto focus picks a surface and focuses on it. Expecting it to be the safe surface you want to be in focus is folly. Or I am missing something here.....
12-17-2014, 01:15 PM   #13
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QuoteOriginally posted by aleonx3 Quote
The simplest test you can do is to line up 3 AA batteries; shoot and focus in the middle one at a 45 degree angle, using center focus point. If the photo shows the AA battery in front is sharper than the middle one, you have a FF problem, the opposite is true if the battery in the rear is sharper than the middle, you have a BF problem.
One of my most faithful af test subjects. I might have reached a compromise - at +3 - but that still doesn't change the focus inconsistency...

---------- Post added 12-17-14 at 01:17 PM ----------

QuoteOriginally posted by Mistlefoot Quote
But a christmas tree is not a flat surface. the auto focus picks a surface and focuses on it. Expecting it to be the safe surface you want to be in focus is folly. Or I am missing something here.....
I meant Christmas balls, or a tip of the branches, or a little owl, etc...

---------- Post added 12-17-14 at 01:21 PM ----------

QuoteOriginally posted by aleonx3 Quote
...shoot in 'auto' mode...
In regards to this, in menu 1, AF settings - AUTO AF POINT, gives me only 2 choices (5, or 11 points). Is this valid only for auto, or if one selects - on the dial, camera left - single point, this doesn't matter?

Last edited by Flugelbinder; 12-17-2014 at 01:43 PM.
12-17-2014, 01:25 PM   #14
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QuoteOriginally posted by Flugelbinder Quote
One of my most faithful af test subjects. I might have reached a compromise - at +3 - but that still doesn't change the fact of the focus inconsistency..
Focus inconsistency is entirely different problem which also depend on your lens, lighting condition (especially in tungsten), camera setting and the user. If you set to use only center focus point and set AFS.S to focus priority, you would at least eliminate the chance of erroneous focus (such as common on the back-wall), because you can not release the shutter is the intended object is not in focus.

Last edited by aleonx3; 12-17-2014 at 01:29 PM. Reason: correction AFS.S
12-17-2014, 01:27 PM   #15
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By the way, thank you all for the help! It seems like it might just be that I'm used to smaller af points... I've read (unfortunately after buying the Pentax) in other forums, that there is in fact a problem with the af points being too big. Real life examples are shown, for example in concerts, where the photographer tries several times to focus on the singer's face, but the camera focusses on the mic... This is what I'm observing also.

---------- Post added 12-17-14 at 01:28 PM ----------

QuoteOriginally posted by aleonx3 Quote
...set AFS.S to focus priority...
First thing I checked when bought the camera...

---------- Post added 12-17-14 at 01:40 PM ----------

One more thing, that might be of some importance... This seems to happen only when shooting from a distance, which leads me to believe that the issue is indeed the size of the focus points. Close up, there is not a problem (after the micro-adjustments). I'm using the 35/2.4, if it helps...
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