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12-24-2010, 04:09 PM   #1
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Does my K-r have the autofocus problem?!

Hi, I'm a total noob and got a brand new K-r. After shooting a few hundred photos I recognised tha tnearly half of my pictures are not sharp, but actually this only occurs @ a certain focal length.
I took a test photo(f3.5, 18mm) and focused on an object about 2 metres away. the result was very bad. Only some objects in the foreground were sharp.
When I zoom in to 35mm or more or when I focus @ nearer objects like my hand 0.5m away this problem doesn't occur ...

I took all shots under average light conditions indoor, using the flash.

Beacause I'm I noob I don't know if thats the front focus problem some people post about in this forum. Sometimes the camera does focus strange, sometimes not....

Can you tell me more, please?

12-24-2010, 04:37 PM   #2
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Here a test shot:
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12-24-2010, 05:37 PM   #3
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What was the shutter speed for this shot?

How did you manage to get a red X in the dead center?
12-24-2010, 06:18 PM   #4
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Setting the camera for center point only (instead of 5/11) might help. With that it should focus on what is in the center ring of the viewfinder, otherwise it might choose one or more of the other 5/11 points. Also, consider including EXIF information with test shots, these contain the parameters used (such as shutter time, aperture, ISO, AF-mode etc.) and help making intelligent suggestions :-)

12-24-2010, 06:46 PM   #5
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ok, i took this shot in auto mode, f3.5, iso 200, af.mode: 5/11, and I marked the camera's chosen focus point with a red rectangle(I'm sure this was the only focus point chosen)

I can't tell you the shutter speed, since the information provided by win7 seems to be wrong(1/8) and my cameras battery is completely discharged and I forgot the battery charger at my girlfriends apartment... i guess it was somwhere near 1/20s.

Sorry for the uncomplete informations, this is all I can tell you for now.
12-24-2010, 07:17 PM   #6
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Oh yes, the k-r has the viewfinder focus indicators, so you should be fine in that department :-) 1/8 or 1/20 s sounds pretty slow, you should be able to use 1/180 s which would eliminate blur from camera shake but wouldn't affect the exposure because the flash burst is much faster than that and most of the light is coming from the flash in these conditions; the ambient light may still be enough to make your shots blurry. (You cannot use a faster shutter speed than 1/180s with flash due to the way the shutter operates; a faster speed would result in some of the frame missing that fast flash burst.) The camera should meter the light from the flash during exposure and cut the flash pulse short when (if) there is enough (TTL), so you might be able to use a smaller aperture which would help with sharpness too.
12-24-2010, 07:32 PM   #7
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so to make this clear: my camera is ok, it has nothing to do with front focus, its only because of wrong adjustments the auto mode took?!(strange, shouldn't be the auto mode at least that intelligent to take a few good fotos when using the flash?!?!?)

Smaller aperture is a good idea but it would only cause a greater depth of feeld , which would cover the effect that the actual area I focused on is not in focus... but would not help me figure out why the area is not in focus...
12-24-2010, 07:58 PM   #8
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The idea is to eliminate other causes than lens or camera. I'd say the jury is still out.

I suppose the k-r is similar to the k-x: one would expect it to use 1/180s with flash and maybe an aperture to suit the focus distance (in AUTO PICT, at least). Unfortunately it doesn't.

12-24-2010, 09:12 PM   #9
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What lenses do you have? If just the kit lens it's going to be next to impossible to verify if your camera is front-focusing. This is because it's not "fast" by design. In other words, its aperture doesn't open enough to permit shallow depth of field. This is required to prove beyond a reasonable doubt that your camera has focus issues. Make sense?
12-27-2010, 07:00 AM   #10
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interesting, while shooting in "moving objects" mode the k-r uses 1/180 shutter speed, in auto always 1/30 or 1/40...
I took a few test pictures and showed them a friend of mine who's been a passionate photographer for years.
After looking @ the photos and playing around with the camera itself she told me that my camera defenetly has focus issues.

After setting custom autofocus fine adjustments to -10 results seem to be ok with a chance of ~80% - 90%.. decreasing with focal length...
Meaning wide angle shots are still not that great..

I will give it a try and send in the camera to a service point in germany...

To be honest I'm pretty dissappointed, imho it's just very impudent to send a camera with this configuration to an customer.

Thank' for your help anyways!

@krebsy97: Sry but I really dont understand why I shouldn't be able to tell if my camera has front focus(maybe I confuse this term with "it's not focusing where I want it to)
Even if depth of field is not that great with f3.5 in comparison to f1.4(for instance) but after looking @ the photos on an high resolution monitor you can tell the difference very well between the area in focus and the rest.

If you had looked @ my example Image closely you would have seen that the area i focused on is just NOT IN FOCUS while objects nearer to the camera get sharper and sharper...
12-27-2010, 04:55 PM   #11
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Isn't the depth of field with any lens that is wide open, basically the same - little or nothing? Meaning that the DOF on a f:4.5 lens, wide open, focused at 12 feet the focus point would be 12 feet, with little or no DOF, just as an f:1.4 lens, wide open, focused at 12 feet have the focus point at 12 feet and the DOF little or none? I guess what I am getting at is that as long as you do your focus testing at wide open, that would be the most critical focus and the maximum aperture of the lens wouldn't enter in.

In the included shot, I believe it is at 1,024 resolution, and can't tell if it was shot that way, or shot at the maximum resolution the camera can muster. Might be you had to reduce the resolution to add it to the post. I can't tell from the EXIF available whether the lens was wide open or stopped down, etc. You might set up a more graduated test to try to determine if the focus is acceptable and view it in a maximum resolution setting.
12-28-2010, 03:18 AM   #12
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the photo was automatically reduced in resolution when i added it.

As I mentioned above the aperture was @ f3.5

Do you mean with "most critical focus" that it's a good or a bad Idea to test the focus on wider angles?

Tomorrow I will link a few test shots with 1/180s and f3.5 @ wide angle in full resolution.
12-28-2010, 05:31 AM   #13
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QuoteOriginally posted by hallenti Quote
Isn't the depth of field with any lens that is wide open, basically the same - little or nothing?
...
For the same focal length DOF is narrower with physically larger apertures (smaller f numbers). There is quite a bit of difference between, say 1.4 and 3.5. Also, longer focal length and smaller distance to subject decrease DOF.
12-28-2010, 04:15 PM   #14
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It is better to judge the lens wide open as that is where the most critical focus would be. With the aperture shopped down (a higher number) you will have greater depth of field and thus the focus won't be as critical. So, wide-open should show a shallower area of focus than stopped down.
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