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12-23-2010, 08:56 PM - 1 Like   #1
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K-r Focus Test with Images

Last night I spent some time checking the AF accuracy on my K10D, K20D and new K-r. This was done to see if my K-r was front-focusing like I expected. The results, unfortunately, speak for itself.

My test configuration consisted of the following:
  • Camera mounted on tripod and positioned at a 45 degree angle towards focus test chart. (See Nikon D70 Focus Chart)
  • 2 second delay to minimize camera shake.
  • Custom white balance performed.
  • Center-point focus selected.
  • Center-weighed light metering.
To see if patterns existed, I used three different prime lenses (DA 40mm; DA 35mm Macro; FA 50mm). I also performed separate tests for tungsten and daylight-balanced lighting.

For now I will just post images that were captured using the FA 50mm f/1.4. The results were identical across all lenses I tried. You will clearly see that both the K-r and K20D front-focus in tungsten light. The K-r, however, is in a league of its own. Even with the focus adjusted to -10, front-focus is still an issue.

The results were much better once daylight-balanced bulbs were screwed in. The K-r still front focused but its performance was acceptable.

I apologize in advance for the lousy exposures. I was concentrating on getting things lined up and focused properly.

_______________________________________________________________________________________________________________________________
Without further adieu, here are the images:

K-r w/FA 50mm f/1.4 (Tungsten):



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K-r w/FA 50mm f/1.4 (Tungsten) FOCUS ADJUSTMENT SET TO -10:



_______________________________________________________________________________________________________________________________
K20D w/FA 50mm f/1.4 (Tungsten):



_______________________________________________________________________________________________________________________________
K10D w/FA 50mm f/1.4 (Tungsten):



_______________________________________________________________________________________________________________________________
K-r w/FA 50mm f/1.4 (Daylight-Balanced):



_______________________________________________________________________________________________________________________________
K-r w/FA 50mm f/1.4 (Daylight-Balanced) FOCUS ADJUSTMENT SET TO -10:



_______________________________________________________________________________________________________________________________
K20D w/FA 50mm f/1.4 (Daylight-Balanced):



_______________________________________________________________________________________________________________________________
K10D w/FA 50mm f/1.4 (Daylight-Balanced):




Last edited by krebsy75; 12-24-2010 at 02:31 PM.
12-23-2010, 09:02 PM   #2
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I hope current and prospective K-r owners find this post helpful. Please keep in mind that this test was in no way scientific. Having said that, the pattern was clear and was reproduced on all three lenses I tried.

I am exchanging my K-r tomorrow with B&H. I'm not confident a replacement will be better, but my wife wants me to give it a shot. If number two has the same defect we are going to punt for now until this problem gets resolved by Pentax.
12-23-2010, 09:13 PM   #3
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There is one more point I want to make. I don't think it's wise to have your K-r "calibrated" for this issue. Your best option is to wait for a firmware update if you cannot return it. I don't see how a service provider can resolve just the tungsten specific problem.
12-23-2010, 10:14 PM   #4
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Thank you for the test shots krebsy. It really is a shame that the camera was allowed to leave the factory floor with this defect, but, such is life. Hopefully your replacement will be better, but I too am not holding my breath.

12-23-2010, 11:01 PM   #5
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Good luck! Those are dramatic looking photos, I'd be heart broken to see those on my camera
12-24-2010, 01:03 AM   #6
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QuoteOriginally posted by neurocyclist Quote
Thank you for the test shots krebsy. It really is a shame that the camera was allowed to leave the factory floor with this defect, but, such is life. Hopefully your replacement will be better, but I too am not holding my breath.
that kinda defects are also similiar in even pro bodies and 5thousand dollars lenses so send ur camera with all ur lenses to be calibrated together
12-24-2010, 01:32 PM   #7
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QuoteOriginally posted by krebsy97 Quote
There is one more point I want to make. I don't think it's wise to have your K-r "calibrated" for this issue. Your best option is to wait for a firmware update if you cannot return it. I don't see how a service provider can resolve just the tungsten specific problem.
Hmm... I'm not good at reading focus charts, but what i see on the Kr is:

a. Kr in Tungsten was perhaps -14 OOF

b. Kr in Tungsten with -10 adjustment, was perhaps still -8/9 OOF

c. Kr in White Balance with -10 adjustment was pretty much in focus.

If the camera was calibrated to -10, wouldn't that enable the Tungsten FF to be corrected by a -4 adjustment in camera. When i shoot indoor live theatre in tungsten, i would commonly dial in a -4 in my K20 for my Tamron 28-75 lens and then remove it after the rehearsal was over. As far as i know, most slrs shift to FF in tungsten lighting.

But i agree with exchanging the camera, it shouldn't be necessary to calibrate a new camera for focus. But i don't see anything necessarily abnormal with the FF in tungsten. (but i can't explain why the initial attempt to focus the camera for tungsten wasn't as effective as the -10 adjustment would indicate). What seems to me is wrong is the factory calibration wasn't adequate.

(note i haven't been reading the Kr forum lately so if this is a general problem, then i''m not aware of it :-))

Best wishes with your second camera,
12-24-2010, 02:20 PM   #8
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Did you take notice to how the K10D performed? It was dead on in daylight-balanced lighting and a few tics off in tungsten. And this is a 4 year old camera. Eons in digital photography.

It looks like my K20D could use a calibration. I plan on sending that out with a lens. Once calibrated I'll adjust accordingly in tungsten and all should be well.

The K10D has become my reference. It proves that, at least 4 years ago, technology existed to get focus close to 100% in typical lighting conditions.

BTW: In case anyone is wondering, I performed focus tests for both the K20D and K-r twice with the FA 50mm f/1.4. And I did it twice in both lighting conditions. The results were the same. Again, hardly scientific but convincing enough for me.

Have a Merry Christmas, everyone. And if your new camera is having focus issues while getting shots in tungsten light tonight, take heart in knowing that D7000 owners are feeling the blues, too. See: [D7000] - Problems (Bad Pixels) Nikon Rumors Forum

QuoteOriginally posted by philbaum Quote
Hmm... I'm not good at reading focus charts, but what i see on the Kr is:

a. Kr in Tungsten was perhaps -14 OOF

b. Kr in Tungsten with -10 adjustment, was perhaps still -8/9 OOF

c. Kr in White Balance with -10 adjustment was pretty much in focus.

If the camera was calibrated to -10, wouldn't that enable the Tungsten FF to be corrected by a -4 adjustment in camera. When i shoot indoor live theatre in tungsten, i would commonly dial in a -4 in my K20 for my Tamron 28-75 lens and then remove it after the rehearsal was over. As far as i know, most slrs shift to FF in tungsten lighting.

But i agree with exchanging the camera, it shouldn't be necessary to calibrate a new camera for focus. But i don't see anything necessarily abnormal with the FF in tungsten. (but i can't explain why the initial attempt to focus the camera for tungsten wasn't as effective as the -10 adjustment would indicate). What seems to me is wrong is the factory calibration wasn't adequate.

(note i haven't been reading the Kr forum lately so if this is a general problem, then i''m not aware of it :-))

Best wishes with your second camera,


12-24-2010, 07:21 PM   #9
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If you have a chance, will you try to replicate this using the "battery" method of testing focus? I was testing my 16-50 lens using this same focus chart and ended up with poor results (FF at one end BF at the other). However when I tested it using staggered batteries, the focus seemed to not have the problem. (Both were under daylight, I'm more interested in the validity of the test chart than the tungsten problem)
12-25-2010, 03:31 AM   #10
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Your findings mirror exactly what some of us have been reporting at the K5 forum. The FF in tungsten is so strong that even a -10 AF adjustment isn't enough to correct it. I've also found (like you've shown here with K20d) that an older model (K-x in my case) performs flawlessly where the newer model doesn't.
12-27-2010, 08:53 PM   #11
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I ended up punting early on the K-r and didn't accept an exchange. Once the bugs get worked out in these new cameras, I'll be back on board.

Last edited by krebsy75; 12-27-2010 at 09:34 PM.
12-30-2010, 11:17 AM   #12
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I received a K-r kit yesterday and have been trying a few shots with the kit 18-55 lens today. It seems as though it focuses pretty well under artificial light, a Verilux "natural sunlight" lamp. (Perhaps I should carry one around with me?) I'm hoping that it is okay.


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12-30-2010, 12:45 PM   #13
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OK Guys, forgive my ignorance here. Why is this issue important? if You took say a portrait shot with the camera, would the face be out of focus? Why can you not just lift the camera a minute tad to compensate?
I'm not trying to be difficult, far from it, I am trying to understand how it would effect (and by how much) using the camera in everyday life?
If I had a Kr and was unaware of the problem and took a pic of a sparrow in a tree (close up shot for example) would the sparrow be out of focus?
regards
woody
12-30-2010, 03:21 PM   #14
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What was the focal length for this shot?

It's going to be hard to perform this test with the kit lens since its aperture doesn't open up enough to permit razor thin depth of field.

QuoteOriginally posted by kpevav Quote
I received a K-r kit yesterday and have been trying a few shots with the kit 18-55 lens today. It seems as though it focuses pretty well under artificial light, a Verilux "natural sunlight" lamp. (Perhaps I should carry one around with me?) I'm hoping that it is okay.


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12-30-2010, 03:29 PM   #15
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This issue only becomes apparent when depth of field is fairly thin. At smaller apertures imperfect focus won't be visible.

I happened to notice the problem while using my FA 50 f/1.4 in tungsten light. I wanted to see how the shots looked without a flash and the ISO revved up. While reviewing the shots it was obvious that the camera wasn't focusing where I wanted it to. That's when my investigation commenced.

QuoteOriginally posted by ukwoody Quote
OK Guys, forgive my ignorance here. Why is this issue important? if You took say a portrait shot with the camera, would the face be out of focus? Why can you not just lift the camera a minute tad to compensate?
I'm not trying to be difficult, far from it, I am trying to understand how it would effect (and by how much) using the camera in everyday life?
If I had a Kr and was unaware of the problem and took a pic of a sparrow in a tree (close up shot for example) would the sparrow be out of focus?
regards
woody
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