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06-16-2013, 02:11 AM   #1
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K-5 Mid Range Auto Focus Error with Fast Lens

I am increasingly convinced there is something wrong with my K-5's AF system. I have had the system check out by Pentax once already and they say it performs within specification. So here is my problem. I like to shoot wide open with my limited and more often than not shot at mid range are just plain soft. I have noticed that even when the camera says the images are in focus, they are in fact not in focus. The focusing error doesn't happen very often if I just let the lens go out of focus then regain focus from one or the other extremes. However, when focusing from one mid range object to another, the focus confirmation blips but the focus ring is not moving and shots are OOF. I have kind of given up on my K-5 AF system at this point and have been using bracketed manual focusing instead for any picture requiring f4.0 or larger fstop. I have updated to the latest firmware and it has not solved this problem.

I would like to know why did Pentax say my K-5 is within spec when the AF system is obviously not working properly. Can it even be fixed or is a new camera the only solution. Has anyone experienced the same thing with their K-5? K5II? This K-5 AF system is by far the worst AF system I have ever used - it's quite ridiculous.

06-16-2013, 03:08 PM   #2
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QuoteOriginally posted by chesebert Quote
...Has anyone experienced the same thing with their K-5? K5II? This K-5 AF system is by far the worst AF system I have ever used - it's quite ridiculous.
Yes, in fact I've been holding off posting about this issue, thinking that perhaps some more test will give me some clues. But after yesterday's shoot I felt it was time to post.

I don't know what you call mid range, but with my FA43, I've been getting sharp shots of close ups or half body shots. As soon as I back up for full body shots, they come out completely out of focus - pretty well consistently, even at f8. Having said that, I haven't really made a point of taking similar shots in daylight, but I've never noticed the problem in my daylight shots.

The only thing I have yet to try is play with the AF Adjustment. Since I'm already at effective +14 (after using PK Tether to shift the zero point), I intend to try to go a bit higher and see if it helps. I'm thinking of the possibility that the lens may be happier with more than the +14 at the particular distance I'm having problem with. Another thing I haven't tried is forcing the lens to first focus on something that is at a very different distance than my subject, before refocusing.

Sorry, I have no solution for you.
06-16-2013, 03:29 PM   #3
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I'm using a k5iis now, though i still have the k5. Unfortunately, I don't think I can help you as I've had good luck with the focusing on the k5 with multiple fast lenses. Granted, in low light, the focusing speed was not always as fast as I'd like so that's why the k5iis was purchased. Here's a set taken w/ the k5 and 43 limited:

fa43 and k5 in low light

Here's a set taken w/ the k5 and 77:

Dinner @ Jo and Tony's - a set on Flickr

So does this happen in all types of light or is it as was described by bxf an issue under incandescent or flourescent light? And what focus method are you using? Care to post some samples?

Personally, I always use spot focusing, never use center point and recompose. So if I'm shooting portrait mode, I'll move the focus point up and usually aim for the head or chin/neck area. Have you tried using a tripod and really testing out your focusing? Sounds like you've been having this issue for a while so it sounds like it's time for some more testing on your own - and maybe you can include some pics and descriptions when/if you send your camera back.

Good luck...
06-17-2013, 01:55 AM   #4
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QuoteOriginally posted by chesebert Quote
I am increasingly convinced there is something wrong with my K-5's AF system. I have had the system check out by Pentax once already and they say it performs within specification. So here is my problem. I like to shoot wide open with my limited and more often than not shot at mid range are just plain soft. I have noticed that even when the camera says the images are in focus, they are in fact not in focus. The focusing error doesn't happen very often if I just let the lens go out of focus then regain focus from one or the other extremes. However, when focusing from one mid range object to another, the focus confirmation blips but the focus ring is not moving and shots are OOF. I have kind of given up on my K-5 AF system at this point and have been using bracketed manual focusing instead for any picture requiring f4.0 or larger fstop. I have updated to the latest firmware and it has not solved this problem.

I would like to know why did Pentax say my K-5 is within spec when the AF system is obviously not working properly. Can it even be fixed or is a new camera the only solution. Has anyone experienced the same thing with their K-5? K5II? This K-5 AF system is by far the worst AF system I have ever used - it's quite ridiculous.
I am experiencing a similar problem. With the DA 50-135 my K-5 doesn't focus well at 50. I have to zoom to 135, focus, then zoom back out to ensure sharp images. With the FA 50 1.7 it's a constant battle with back focus.
The 16-45 behaves much the same as the 50-135. Surprisingly, the 12-24 seems to work a lot better over its range.
Someone pointed out that a lot of the problem relates to the central focus guides. If you have your main subject, and anything else in the background near the guides, it's anyone's guess as to where it will focus.
It seems the actual focus area is quite a bit larger than the guides indicate.
I agree with that.

06-17-2013, 01:25 PM   #5
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Is this why the SAFOX X autofocus system was introduced on the K5II to improve autofocus for lenses with wide apertures ? To quote Pentax "This increase the AF accuracy drastically when using with very fast lenses"
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