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04-18-2010, 12:23 PM   #1
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K-x focusing

My K-x is having troubles giving me a clear blurr-free shot at medium-slow speeds (1/50 to 1/100) and even at speeds of 1/120. It seems to me that's a speed sufficient enough for hand held shots but there's always a blurr. Vertical shots looks worse, I've tried SR on and off, can't tell if it helps, I think not.

Is there a known problem with K-x's AF ?

My usual settings are : P or A mode
ISO between 200 and 800
AF single center point
Evaluative metering
Wide apertures
SR on
Sample shots to come.

04-18-2010, 12:31 PM   #2
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Well to me speeds that slow would most likely cause some motion blurring. I know that when I do rolling shots of cars I usually set the shutter speed to 1/60 and you have to be very still or motion blurring will become a problem. When you post some photos of the problem we should be able to discover the problem quickly.
04-18-2010, 12:57 PM   #3
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Here is a shot taken today :
1- f/4.5 1/200sec ISO 100 SR on. (resized)


100% crop


I know the resolution is bad due to resizing but the problem is shown here.
04-18-2010, 01:36 PM   #4
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The tree in the crop doesn't look very in focus, but what makes you think that's where the camera focused? You're shooting at a pretty wide aperture here (f/4.5), so the DOF is not very deep. Looks like the camera may have focused on the rock instead of the tree. Did you select a focus point or let the camera decide?

04-18-2010, 01:41 PM   #5
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I agree, it looks a little blur and very flat.
Looking at the branches in the background, I'd say they are in focus.

I can see 2 options:
1) The camera (= you?) focused on the background
2) The camera is back-focusing

See:
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The branches look fine and sharp.

The picture lacks contrast, crispness and sharpness though, things you could add in post processing, or by changing the camera parameters.

- Bert
04-18-2010, 02:26 PM   #6
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Thanks to all for the clarifications.
I always use center point AF because the K-x doesn't display witch point it uses so I make my focus on what I want and then re.... (how do you say "recadrer" in english ???), re-frame my shot, so here I'm pretty sure I made my focus on the dead tree in the fore ground.

bymy141, you talk about back-focusing, what is this ? I've seen topics about this and how to adjust it on the K-x but that's about all. It's a bit much for my understanding of things !
So please continue with your suggestions.
04-18-2010, 09:52 PM   #7
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The word you are looking for is "recompose".

There is next to zero chance that what you are seieng is backfocus. That would be if the camera agrees with you about where the focus should be, but misses focus by a millimeter or two. You are seeing soemthing very different. What you are seeing is that the center point is not a "point" at all but a fairly large rectangle. So just because you aimed it at that tree doens't mean other parts of the scene weren't in range of that focus sensor.
04-19-2010, 12:31 AM   #8
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QuoteOriginally posted by lucm70 Quote
Thanks to all for the clarifications.
I always use center point AF because the K-x doesn't display witch point it uses so I make my focus on what I want and then re.... (how do you say "recadrer" in english ???), re-frame my shot, so here I'm pretty sure I made my focus on the dead tree in the fore ground.

bymy141, you talk about back-focusing, what is this ? I've seen topics about this and how to adjust it on the K-x but that's about all. It's a bit much for my understanding of things !
So please continue with your suggestions.
Back focus or Front focus means that your camera auto focus system is not tuned well in the factory. If that is the case all shots will be out of focus by the same relative distance (depending upon physical lens offset).

On some Pentax camera's (K20D and K-7 I know for sure) you will have a custom menu setting that allows users to fine tune the AF system for all and/or a specific lens. I do not have a K-x, so I don't know if that option is available for you.

If it is not, you could however access it through the debug menu.
How to get into the debug menu is described here: Debug mode
And you can read a discussion on the subject here: http://forums.dpreview.com/forums/readflat.asp?forum=1036&message=33983956&q...ebug+mode&qf=m

How to properly calibrate the AF system is described here: Jeffrey Friedl's Blog Jeffrey’s Autofocus Test Chart

I hope this helps.

- Bert


Last edited by bymy141; 04-19-2010 at 12:46 AM.
04-19-2010, 01:29 AM   #9
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wind moving the trees? 1/100 is pretty slow.
04-19-2010, 06:18 AM   #10
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Well, I think you're all about right !
And I think Mark S. nailed a bit of my problem : Center point AF is not really a "point" but more of an area. And my shooting speed might be a bit slow.

I'm new to this DSLR world and I found that my old Panasonic bridge FZ18 had a really great lens stabilization that could make a 1/30 sec shot sharp and a very pointy center AF, so I must keep on trying and learning.

Thanks to all, and I think the case is closed !
04-19-2010, 07:45 AM   #11
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QuoteOriginally posted by lucm70 Quote
I'm new to this DSLR world and I found that my old Panasonic bridge FZ18 had a really great lens stabilization that could make a 1/30 sec shot sharp and a very pointy center AF, so I must keep on trying and learning.
I do not agree.

There is no motion blur in this picture. See the background branches.

You did not suffer from slow shutter speed motion blur.
And for trees to be blur due to the wind at that shutter speed you need a very strong wind.
I think the probability of motion blur is very low.
It is just out of focus.

Also, my Lumix FZ gives me a lot more sharpness out of the box than any given DSLR.
Try to add some in PP.

- Bert
04-19-2010, 09:35 AM   #12
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I have to agree with the above comment that this is not a shutter speed problem. Now that I have seen a photo I am also going to say that the camera did not focus correctly due to the trees in the background looking quite sharp.

I think that next time I would bring a tripod and stop the lens down as well. This would assure a sharper picture so next time you go out give this a shot and post up the results. Hopefully we can figure out what this is and if it is the camera you can send it back and get it repaired.
04-19-2010, 10:45 AM   #13
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Wow ! There's so much to read on this forum about un-satisfied K-x users regarding image sharpness, there's got to be something wrong.
The SR / Mirror slap thing looks like a common problem and I must say that I use SR almost all the time.
I'll keep on reading !
04-19-2010, 02:01 PM   #14
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QuoteOriginally posted by lucm70 Quote
Wow ! There's so much to read on this forum about un-satisfied K-x users regarding image sharpness, there's got to be something wrong.
The SR / Mirror slap thing looks like a common problem and I must say that I use SR almost all the time.
I'll keep on reading !
Please do, and don't rush to judgement. A lot of K-x users are relative new-comers to DSLR's. Not all of their camera issues are specifically K-x related, but have alot to do with the difference between shooting with point-and-shoots and DSLR's.

Point and shoots, due to their tiny sensors, have massively greater depth of field compared to most DSLR's, for one thing, a fact which produces most of the observations people have about how 'sharp' their P&S images are compared to their new DSLR's in casual use.
04-25-2010, 01:41 PM   #15
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Luc, have you updated your camera's firmware to the latest "hidden" firmware revision (see Latest Firmwares (Versions & MD5) for Pentax Cameras: Pentax SLR Talk Forum: Digital Photography Review) ? Make sure you use freshly charged batteries before you do, however !

Last edited by RBellavance; 04-25-2010 at 04:24 PM.
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