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06-15-2010, 07:43 PM   #1
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Kx Back Focus???

Hello,

It has been suggested to me that my Kx may have a back focus issue with one of my non Pentax lenses.

Does the Kx have a software fix for adjusting back focus and if it does, does it remember the specific settings for each lens?

If it is a mechanical setting can someone explain the where and hows of it? I do not like the idea of a mechanical fix as I do not want to mess up the great pictures it takes with the 55-300 kit lens.

Thoughts on back focus and the Kx, please...





Thanks!

06-15-2010, 08:20 PM   #2
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There is a backfocus adjustment hack, but it applies the same setting to every lens.

So any adjustment to 'fix' one lens will likely throw another lens out of whack.

Also worth reading for info:
LensRentals.com - "This lens is soft" and other myths
06-15-2010, 08:42 PM   #3
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There is an AF adjustment in the debug menu. A google search will find you the instructions. As rawr said though, I think it is a global adjustment (affects every lens). However, Pentax are able to adjust AF for individual lenses - I just had my K-x and FA 31mm AF adjusted because of a back focus issue.

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06-15-2010, 09:55 PM   #4
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As the two previous just stated, the focus adjustment is across the board and you would have to send it into pentax in order to do an adjustment for a single specific lens. If you do decide to do the debug menu adjustment I would read as much information as you possibly can before attempting to enter the debug menu (if you have not done it before).

06-15-2010, 10:15 PM   #5
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Pentax Canada was able to match AF of my BF DA14 & K-m w/o affecting my other lenses, but it cannot be done with the global setting in the debug mode. Both the camera and the lens must be sent in for adjustment. I wonder what they would do with third party lens though.
06-15-2010, 10:38 PM   #6
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QuoteOriginally posted by GingerBeer Quote
However, Pentax are able to adjust AF for individual lenses - I just had my K-x and FA 31mm AF adjusted because of a back focus issue.
Correct but to my knowledge they will not adjust for 3rd party lenses. Might be country dependent.

QuoteOriginally posted by GingerBeer Quote
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06-16-2010, 03:13 AM   #7
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Is this a big problem with the K-X? I am getting a bit worried about mine. It's due here tomorrow and has thirs party lenses with it as well as the 18-55 kit lens.

I hope it's all ok?

Kerri
06-16-2010, 10:02 AM   #8
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No, it's not a problem specific to the K-x. Every single AF camera ever made is susceptiple to slight discrepancies in focus. People just didn't worry about it until pixep peeping on high resolution digital SLR's made those slight discrepancies more noticeable. And then the paranoia surrounding the issue causes people to imagine problems that aren't real (because they are not rtesting correctly), inflating the number of people who say they have problems.

But there is no more reason to be concerned about focus on the k-x than on any AF camera ever sold.

06-16-2010, 02:41 PM   #9
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QuoteOriginally posted by mertle Quote
Is this a big problem with the K-X? I am getting a bit worried about mine. It's due here tomorrow and has thirs party lenses with it as well as the 18-55 kit lens.

I hope it's all ok?

Kerri
Relax. You will have no problems. In the real world of shooting actual stuff, rather than shooting wonky test charts and then viewing the results at 100% on a computer monitor, few people ever have any issues.
06-16-2010, 03:08 PM   #10
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Marc is right. The same issue exists with film cameras, it just isn't noticed as much because people don't usually make big enlargements of a tightly cropped areas.

Example:
My monitor is 12" high/1050 pixels. If I display and image so that it is 8" high, that would be 693 pixels. The original image is 3136 pixels high. If I now look at it at "actual Pixels" size, rather than "fit Screen", I have essentially enlarged the image approximately 4.5 times (3136/693). Pixel peeping is like looking at the 8x10 print through a 4.5x loupe and wondering why it looks soft and grainy.
06-16-2010, 07:31 PM   #11
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Thanks guys, I was getting a bit worried there! Am looking forward tot he K-X getting here so I can have some fun!
06-16-2010, 07:38 PM   #12
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Well... this isn't a case of shooting wonky test charts or looking for great shots at 3136 high. In fact, I usually shrink photos to about 30% for the web and print at 8X10 for contest entries. The camera is taking great shots with the 55-300. I'm not getting very good shots at any size from another that seems to take good shots on a different camera. On mine I get un'shoppable' poor for the most part.

Working to tolerances myself, I can accept the LensRental theory. The lens is good, the camera is good... they're just not good together. I was hesitant to contact the manufacturer at first as I thought I might just need to get used to a new camera... after many shots in many conditions, I should have been sending it back to see if I can get one that gets along a little better.

AhhhWelllllllll... .. .

But I'm not going to do anything to affect the quality of the shots the long one gives me... it's the one I had low expectations of and it's the one that's shining. Go figure.

Thanks for the thoughts.
06-17-2010, 12:14 PM   #13
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There's about half a million things that could potentially cause bad pictures, and while lots of people are quick to assume back-focus or front focus, that's actually not one of the most common reasons for problems. I'd start by posting test images that clearly demonstrate the problem you are seeing.
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