K10/K20 focus

I have taken a few close up images with the new K20D with the focus not what as expected.
Have many others had poor experiences with their autofocus?

To check I downloaded a chart from here -
http://www.zimbio.com/Digital+Cameras/articles/839/AF+adjustment+test+chart+help+Pentax+K20D
and had a play. The test result looks fair.

Lens at 250mm F4 - This was the result

This is actually not too bad imo. What lens is it : Is it wide open : I suspect it may be the 18-250 but that doesn't go to f4 at 250mm, does it :

If you look at the imperial scale down the right, it looks as if it's front focussing a tad because shaarp focus is at about 1/8".

Only a gnats willy in it Peter would you adjust it or not:

You should try using a focusing target such as the one in Yvon Bourque blog, or one that has a black line in a white circle. This one has so many lines in it that , even if your focusing sensor is off, it will find something to lock on. It seems to me like it is focusing properly, but you cant make sure on which line the focusing sensor has locked on.

The chart is from Yvon Bourgue (well that's what it says on it), I have just set function 35 (AF adjust) in the custom menu to -2 and had another pop, it makes the auto focus look better at 100%.

Your right on both counts it is the 18-250 and it is wider than f4.... must have been thinking of something else when I typed that

I think it would have been f6.3 as it was at max

These were my before and afters so I think you did quite well!

[IMG]http://i223.photobucket.com/albums/dd37/hefty1969/IMGP5284.jpg[/IMG]

[IMG]http://i223.photobucket.com/albums/dd37/hefty1969/IMGP5312.jpg[/IMG]

As you can see, my K10 was back-focussing just a tad

Yvon has a new set of charts. He designed them after those one, and the new ones are also endorsed by Pentax U.S.A.

I think jon is more concerned with the overall sharpness of the lens as opposed to any front or back focusing. As Peter says, its only a tad front focusing.

But if its the overall sharpness you are worried about, I don't think you can get it much better than what you have already.
Shooting at wide open and at 250mm you are not goin to get to many tack sharp shots

I wouldn't adjust it based on that test. I don't personally think that the chart used is the best for the purpose. Yvon Bourke's are much better for focus testing.

hi , I've downloaded the Yvon Bourque charts but after going to the web site i can't find any instructions on how to use them. Help??

1: Set the charts on a desk/table at 45 degrees to vertical.
2: Set your camera on a tripod, centre of the lens level with the centre line of the chart at slightly greater than it's minimum focus distance.
3: Set your aperture to max (smallest f number) and focus mode to AFC and centre spot focus point.
4: Set the lens focus manually to infinity.
5: Use AF to focus on the centre line of the chart.
6: With the camera set to Av mode, take a shot.
7: View the shot on your monitor to properly see whether your chosen lens is forward or back focussing.

I suggest repeating steps 4 - 6 several times for each lens before making your decision to adjust or not.

EDIT: Added the bit about centre spot focus, which I forgot first time round.

You could use anything to test the focus.... better to put a mark on it with tipp-ex so that you can see where you focussed. Don't lay a pen on it like I did below, you may have parallax problems. Look down at it at about 45 deg or less. Focus either manually or AF, but if you do focus manually check first against a vertical object (box or similar) that your manual and AF are the same. Lettering is easy to focus on manually.

I used a free CD back off a camera mag here with a 50mm Macro that I'm having manual focus problems with... OK on this shot though.




shim

Dreaming of the mythical 60-250 perhaps...

Andy

Yes you can, but Yvon's chart removes any ambiguity regarding the actual focus point, as there is only one high contrast target.