AF adjustment issue

krypticide · 03-14-2009, 02:53 PM

So after botching a paid photoshoot because of bad focusing when shooting the FA 35mm f/2 wide open (I know, I know...), I decided to do the AF adjustment for all my lenses.

Problem is, all except one of them is at -10 (the exception is at -7)! And they are still front focusing slightly.

Is there something wrong with my body? Seems unlikely that all my lenses would be front-focusing.

**Marc Sabatella** · 03-14-2009, 04:53 PM

If you're testing using tungsten lighting, then yes, every lens will front-focus slightly.

Causes of back&front-focus are still poorly understood (at least by me), but everything I've read suggests to me that *most* problems that occur would be with the body, not lenses, since the body is the brains behind the operation and in theory performs a double check of the focus. A misaligned AF sensor would indeed reuslts in all lenses being "off" in the same direction (if not the same amount).

Parallax · 03-14-2009, 04:58 PM

With all of your lenses being off by essentially the same amount, and in the same direction, I would suspect a body issue but Marc is right about the lighting. If you haven't done so already, repeat the tests at or near infinity under natural or fluorescent light.

krypticide · 03-14-2009, 06:17 PM

I'm doing it with a focus chart at 45 degrees and near minimum focus distance. I'm doing it under fluorescent light. I'll try under daylight and see if that helps.

krypticide · 03-14-2009, 06:37 PM

Yep, same results as the first time. Going to call Pentax.

enoxatnep · 03-17-2009, 07:26 PM

Originally Posted by krypticide

I'm doing it with a focus chart at 45 degrees and near minimum focus distance.

I'd be a little wary of the results you get from those downloadable focus charts that ask you to set them up at 45 degrees. I was all freaked out by my 50mm f1.4 supposedly front-focusing, and no degree of in-camera AF adjustment worked. But then when I tested on real-world subjects that were perpendicular to the lens (text on a calendar, etc.), the AF was very good most of the time. (The AF would miss on occasion - no camera's perfect - but the in-focus shots were bang-on.)

Other threads in this forum have also indicated how the actual area of an AF point extends in a circle beyond the little red rectangle in the viewfinder, so your camera may indeed be locking focus on something above, below, or to one side of a focus point. This might give the impression as well that your AF is out of whack.

*pingflood* · 03-17-2009, 07:39 PM

I would say it's a body issue. -10 is a SIGNIFICANT adjustment and if all the lenses except one are maxed out there you probably need to send your camera to Pentax for a little tweaking.

krypticide · 03-17-2009, 11:30 PM

Just ordered a K20D from Amazon, will see if that one is better.

Also, I found Jeffrey Friedl's focus chart to be a better one, because it utilizes gray text (and you can pick the shade!) around a solitary black box, making it pretty much impossible for the AF point to mis-focus. The D70 test focus chart has a thin black box around the main black box, which might cause focus problems.

In any case, Jeff's focus chart also showed front focus beyond adjustment ranges.

*NeverSatisfied* · 03-19-2009, 08:39 AM

Originally Posted by krypticide

Just ordered a K20D from Amazon, will see if that one is better.

Also, I found Jeffrey Friedl's focus chart to be a better one, because it utilizes gray text (and you can pick the shade!) around a solitary black box, making it pretty much impossible for the AF point to mis-focus. The D70 test focus chart has a thin black box around the main black box, which might cause focus problems.

In any case, Jeff's focus chart also showed front focus beyond adjustment ranges.

Hi Krypticide, say do you have a link for that focus chart you like? Some of us might be interested.

Have you tried Yvon Bourque's chart (Yvon is known as "K10DBook", if you search this forum)? I just used it to correct my K10D body using the debug menu, that whole experiment really was quite an interesting and satisfying experience. And FWIW, it all started AGAIN when I tried out my new FA 35 on the K10D (now relegated to back-up), "just for the heck of it", only to find that it was back-focusing! Darn that FA 35!

(Actually an absoltely wonderful lens that has prompted me to work the bugs out of BOTH my camera bodies!)

Good luck
Paul

Mile High · 03-19-2009, 09:45 AM

You can find Jeff's focus chart here:
Jeffrey Friedl’s Blog Jeffrey’s Autofocus Test Chart

snofox · 03-19-2009, 02:16 PM

I have seen this "debug menu" and "in-camera adjustment" reference before. Does the K200D have these?

**Marc Sabatella** · 03-19-2009, 02:34 PM

Originally Posted by snofox

I have seen this "debug menu" and "in-camera adjustment" reference before. Does the K200D have these?

No, just the K20D. Some older cameras can access a rather simplified adjustment menu via an undocumented "debug" menu meant to be used by service personnel only, but as far as I know, no one has figured out a way to access even that on the K200D. So if testing reveals a problem, the recourse is to send the camera and/or lens in for service.

My experience with focus testing is that it is *incredibly* easy to get wrong, and all sorts of people (myself included) have managed to convince themselves they are seeing focus problems that don't really exist.

*woodworm* · 03-19-2009, 02:49 PM

Originally Posted by Marc Sabatella

If you're testing using tungsten lighting, then yes, every lens will front-focus slightly.

I'm sorry to take this thread off-topic, but can I ask why tungsten lighting would make a lens front-focus?

snofox · 03-19-2009, 03:52 PM

Thanks Marc. That's why I never could find a debug prog. on my 200, not that I think I need one.

Every time I think that I have front focus issues I find that I am shooting close up and wide open at f 1.4 with a normal lens, such as the FA 50. A flower's pistils are clear and sharp, but the rest of the lily is blurred. DOH!!

*Michaelina2* · 03-19-2009, 04:56 PM

Originally Posted by krypticide

So after botching a paid photoshoot because of bad focusing ...

Katz-eye, or one of the $29 Chinese knock-off focusing screens, install it, and 'presto'... no more focusing problems... ever!

Cheers...