K100D autofocus problem

[r.t. dowling]

Last night I shot a dress rehearsal with a K100D and a 50/1.7 "A" manual focus

lens. The only sources of light were the various spotlights and colored lights

pointed at the actors -- needless to say, manually focusing was a bit trickier

than usual. I used the green focus indicator light in the viewfinder to help me

focus, figuring that the camera could probably do a better job than I could.

Unfortunately, about 90% of the 300 shots I took are noticeably out-of-focus.

It was dark, and the viewfinder is small, so I had no way of knowing this when I

was actually taking the photos... everything looked pretty sharp in the viewfinder.

 

So, I guess my question is this: is there something wrong with the AF system in

my camera, or is the focus indicator light simply a gimmick and not to be relied on?<div></div>

[ripley]

If I knew how to insert a hyperlink here, this would be a lot easier. Do a google search for: flickr groups pentax

Then click on the first hit "(Flickr: Pentax (Samsung) DSLR Users (3 per day)"

Under "Discuss" on left side menu, click on "auto/manual focus" link. In addition to the first post called "auto/manual focus", scroll down to the post titled "K100D annoyances/irritations/problems after use?" The information there should be helpful. I'm considering the K100d as I have old k-mount lenses from my K1000 and ME Super that "should" work on it. Looks like it may not be as simple as putting the lens on the camera and going into manual mode tho.

[jason_greenberg_motamedi]

I use a number of manual focus lenses and have found that a split focusing screen is very

very helpful. I installed a Katz-Eye split screen (http://katzeyeoptics.com/) and have been

very pleased. It has had no affect upon either autofocusing or metering. I don't use the

focus indicator simply because it is rather slow.

 

A possibility is that your camera autofocus itself is off. Do you have a problem with out-

of-focus images with autofocus lenses? A few weeks ago, while photographing on

assigment, I noticed that my camera was constantly focusing in front of my subject. Since I

was far away from a repair shop I adjusted the focus myself based on the instructions

here:

 

http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=19960398

 

I can't say I recommend doing the adjustment on your own, but it worked well for me. In

any case, it is worth testing your camera using the focus testing chart here:

 

http://focustestchart.com/focus21.pdf

[michael_mermagen1]

It is possible when you are focusing, that the confirmation light and beep are activated, but in fact it activated while you were focusing and not necessarily when you stopped fosusing. I assume you are using a single focus point as well?

 

Just thinking outloud...

 

Mike

[r.t. dowling]

Thanks for all the suggestions so far. I downloaded and printed the focus test chart and tried it with the MF A-50/1.7 as well as the AF 18-55.

 

The results with the AF 18-55 seemed fine, although the small maximum aperture (especially at 55mm) gave deep depth of field, thus somewhat negating the effectiveness of the test.

 

I tested the 50/1.7 by using only my eyes to determine sharp focus, and then again using the viewfinder indicator light. I tested at 1.7 and at 2.4. At both apertures, the focus was perfect on the shots that I used only my eyes, and noticeably front-focused on the shots that I used the viewfinder indicator light.

 

I guess what it boils down to is that I need to rely on my eyes, and not the indicator, when working at wide apertures... and when working at small apertures, I'll just not worry about it and let the deep depth of field compensate for any slight front focusing.

[r.t. dowling]

50/1.7 at 1.7, eyeballing it.

[r.t. dowling]

50/1.7 at 1.7, using the viewfinder indicator light. Note that the bottom (or "front") 6mm is much sharper than the top (or "back") 6mm, whereas they were equally blurry when I eyeballed it.

[r.t. dowling]

Correction: upon closer examination, when shooting the AF 18-55 at 55mm and 5.6, it actually BACK-focused somewhat. The top 6mm is sharper than the bottom 6mm. Go figure.

 

{sigh}

[jason_greenberg_motamedi]

None of those look particularly troublesome, but rather normal variation. Do you notice that

most of your images, particularly in low light, look out-of-focus? If not then don't worry. I

suspect that Michael's comment about focusing while the light comes on may be a key; I

turned my indicators off because I kept anticipating it, and usually went past...