Kx infinity focus problem

A couple of thoughts -

Are you using any filters? I have a cheap and nasty CPL which prevents focus at infinity.

The file sizes look a little small. Have you got the Jpeg quality set low somewhere?

Stefan, Oggy, I am not using any filters for these shots.

The file sizes are smallish for the two downscaled shots that show the full scene. All the crops are unscaled crops of 1024 pixel maximum size in the larger dimension, the biggest that flickr allows. I shot raw, imported via Adobe Camera Raw into Photoshop CS4 and saved the crops with jpeg setting 12, the highest available. The street scene in original size is a 6M jpeg. So no, no jpg losses anywhere.

And yes, I see a similar effect with the 55-300 DA-L that came with the kit. Had two reasoanble good shots out of six. One of them was not at full focal length, but at 200mm.

I also have a second Tammy 18-250mm with which I took another 4 shots of the radio tower earlier. This one had a better hit rate, with 1 sharp image, 2 reasonably well focused ones and one out of focus, all shot under the same conditions as before. Better, but not really good IMO...

Than it looks like your camera is quite a bit off, get it to the shop and see what they can do.

There is a Russian mod to set it into "service mode" sorry I forgot the name but it's something like that.
It allows you to make adjustments to the camera you can't normally do for the reason you can screw it up.
On of the options is AF adjustment of the AF sensor, that might do the trick most likely but it's all at your own risk so I wouldn't do it since you got warranty on the camera of course.

Sorry, I was miss led about lens correction by the chart in the dpreview review.

Shame really, that should be standard on all new bodies no matter where in the range they are.

Hi Guys

This all sounds too familiar to me. I have a K10 which has a poor spot on focus rate. One blames oneself, the lenses but I let my camera get out of warranty before feeling that it might be a friday afternoon model.

I'm told that other makes of DSLRs show similar autofocus issues as presumably so must the 35 mm big brothers also do (and wouldnt they have had narrower depths of field?)

I wonder how many similarly afflicted Pentax dslrs there are out there?

I was given to undersatnd that if you manually focus then you should get the expected performance from the lens/body combination -which is what I thought I'd read that Wolfson had done in his tests?

Good luck
Geoff

AF is not and never has been perfect. It will be fooled by low light, low contrast and it only knows where you want it to focus if you tell it.

I find the best way is to use centre-point focus only. lock with a half press on the shutter release, recompose and fire. If it's worked you can see it snap in on the focusing screen (I never look at the green hexagon) and if it won't lock then use MF. The DA lenses can be tweaked manually after AF has locked if you're not happy with the precision.

There are lots of other things that can go wrong with the focusing of SLRs, but they need proper repairs, such as to reset the mirror position. This is Critical, so mirrors should never, ever be cleaned by wiping or touched in any way.

The camera has been wrongly calibrated if AF consistently front or back focuses with all lenses when using a single point with subjects with good light and contrast.

Thanks guys for all your help and support. BTW, my sample pictures were all taken with signle focus point (centre) and did have a good contrast. The K100D did not show such issues.

Anyway, I went to the shop today, showed them my samples. They took a few images themselves and the jury was still out, but then they attempted to try my K-x with a Pentax DA60-250mm, and it refused to work with it completely. After that, they just gave me a new one from the shelf. Just did a few test shots of my usual test scenes as the light was fading, and it looks much better - shooting the radio tower I got three out of three with very decent focus. So fingers crossed, the issue might be sorted now

Will let you know how it pans out. Apart from the focus issues I had, the IQ of the K-x is wonderful. Particularly ISO1600 results are quite something, and when I shoot RAW+JPEG, I have to work ACR hard to get a significantly better result than the in-camera JPEG (of course, there are a few options to improve the overall balance). Fantastic little beast - well done, Pentax!

Oh, and a Happy New Year to Everyone

Wolf

Glad to hear you got a good result.

Happy New Year!

My experience with the K10 did improve with the advice that John gave me a while ago. That was to use the AF button for the focus (yes centre point only) and then fire the shutter when the picture presents itself. (this is for football or group subjects). This combination of AF button and shutter release has certainly helped to get those split second shots -thanks again John!

Accepting that auto focus is not perfect does anyone feel that either the KX or the K7 have done anything to improve on the results possible with the K10?

Back to the subject of this thread when we focus manually we surely depend on the accuracy of the lens/mirror/screen distance being identical to the lens/sensor distance. I presume that there is no way a user can check on this other than by taking pictures. I don't know how this thought fits into autofocus methodology -I guess like John mentions the mirror is likely to be a major influence then? Might it be worthwhile for Wolfson to disable the SR function whilst running his test shots?

Geoff

Unlike all the other models, the K20D and K-7 enable AF adjustments to be set for individual lenses, and this can lead to better results when you would otherwise have inconsistencies.

Also the K-7's continuous focusing (AF-C) is faster than the K10/20D's. I've not noticed any difference in general accuracy since the K10D, though.

Glad to hear things have sorted out perfectly for you, nice start of the year.