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05-20-2008, 12:38 PM   #1
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DA* 50-135 Back focusing...is it the lens, or me?

So this drives me nuts. I thought that I saw on here a couple of months ago someone complaining about this exact same thing, which is why i'm wondering if it's my lens, and not just my inability to get great shots every time.

The following photo was taken with the DA* 50-135, 1/250th sec at f/3.5. The focal length was 135mm, ISO 200. Obviously, my focal point was the boys wading through the creek. The autofocus light was centered on them, and it told me that it was focused and ready to go, and this was the result.

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05-20-2008, 04:54 PM   #2
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miss-aligned focus?

I'm starting to suspect myself that the problem could possibly be miss-aligned focus indications. (I mean that the camera focuses a bit to the side of the focus indication mark.)

I just tonight did some shots, and they all front focus, but I realize that the subject has a focus candidate to the front and right at all shots.

Remember having read about this on a good but critical Pentax blog.
05-20-2008, 05:20 PM   #3
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I too have read many stories how the DA* lenses BF or FF. But I am pretty sure Pentax technician is able to calibrate your lenses with your bodies (k100Ds, K10D) and things will be much improved. If you are using k20D, perhaps you can do this yourself. All is not lost!

I did my k100D lens calibration about 6 months ago and pentax technician calibrated all my lenses (except my tammy) to match my k100D. Things are alot better now.
05-20-2008, 07:38 PM   #4
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So I need to ship my K10D and all of my lenses off to a Pentax Service Center to have them do this? Will they calibrate ANY autofocus lenses, even 3rd party ones? How much is this gonna set me back?

05-20-2008, 08:49 PM   #5
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Make sure you are using a single focus point. Looking at the image on screen here, I think the overhanging branch is in perfect focus. The camera will find it easier to focus on a static edge than on a moving one, such as a youngster, and if you have the green position, it will generally grab the closest object (in the 11 points) with a decent contrast edge.
05-21-2008, 04:27 AM   #6
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QuoteOriginally posted by azcavalier Quote
So I need to ship my K10D and all of my lenses off to a Pentax Service Center to have them do this? Will they calibrate ANY autofocus lenses, even 3rd party ones? How much is this gonna set me back?
I believe it is necessary that you send both the body and your lenses. AFAIK, pentax's calibration utility will not work for non pentax lenses. Even if they do, I doubt they will help you with them. For my case, Pentax did not charge anything since my k100D's body is still under warranty. I suspect it would be same for you.
05-21-2008, 05:20 AM   #7
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QuoteQuote:
Make sure you are using a single focus point.
that is something that got me allot when I first started using my K110D and kit lens, I kept thinking BF? but realized that I wasn't paying attention to exactly what the 11 point AF was locked on, and it turns out the lens was fine. of course I only use manual focus lenses now so thats not exactly an issue.
05-21-2008, 06:33 AM   #8
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QuoteOriginally posted by séamuis Quote
that is something that got me allot when I first started using my K110D and kit lens, I kept thinking BF? but realized that I wasn't paying attention to exactly what the 11 point AF was locked on, and it turns out the lens was fine. of course I only use manual focus lenses now so thats not exactly an issue.
I was in Av mode, and had the focus dial set to "select" so that I could choose the point. Then I put it on the center point, pointed it at the kids, it blinked, focused, and then beeped, and I took the picture. It still turned out like it focused on the ground behind them.

05-21-2008, 06:41 AM   #9
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Have you still got that photo on your memory card.
If so have you checked on the image info that it was in fact the center focus point used/selected
05-21-2008, 07:13 AM   #10
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This really is not that hard to figure out, pick up the camera and shoot another image and see what happens.

Reeks of BF though IMHO.
05-21-2008, 10:08 AM   #11
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QuoteOriginally posted by Greg Wilson Quote
Have you still got that photo on your memory card.
If so have you checked on the image info that it was in fact the center focus point used/selected
No, I wiped the card after I downloaded the images. I didn't know that you could do that, though. I'll have to try that out.

I have multiple images like this, from other shoots as well.
06-09-2008, 07:41 PM   #12
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QuoteOriginally posted by hhallman Quote
I'm starting to suspect myself that the problem could possibly be miss-aligned focus indications. (I mean that the camera focuses a bit to the side of the focus indication mark.)

I just tonight did some shots, and they all front focus, but I realize that the subject has a focus candidate to the front and right at all shots.

Remember having read about this on a good but critical Pentax blog.
It's easy to check for misaligned focus points. Install Remote Assistant & connect the camera to a PC using the supplied USB cable. Compare camera’s focus points to that on the monitor screen. Any deviation to the left or right would indicate a misaligned points.
06-09-2008, 08:49 PM   #13
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Checking Autofocus point

If you have the pef file archived on your HS, you can use the EXIF information the camera recorded in the image to discover the actual AF point using any EXIF reader. If you don't have an EXIF reader, try this:

PhotoME - Exif, IPTC & ICC Metadata Editor

It is shareware / freeware.

QuoteOriginally posted by azcavalier Quote
No, I wiped the card after I downloaded the images. I didn't know that you could do that, though. I'll have to try that out.

I have multiple images like this, from other shoots as well.
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