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Old Oct 1, 2010, 10:16 AM   #1
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Default K20D Foucusing By Itself

The other day I picked up a mint Tokina 80-400mm lens (first version, no zoom lock) and attached it to my K20D. The lens works great and is sharp within the expected parameters (ie:soft focus at full zoom F5.6) and while it seems to focus relatively fast in good light the focus mechanism seems to have a lot of torque.

Anyway, while walking around the yard taking some test shots I noticed something strange. While in single shot mode the lens was focusing fine with the shutter pressed halfway down, but in between shots I noticed it was continuing to focus while I walked around without even touching the shutter.

I went and attached several of my other lenses and they were all doing the same thing, some lenses more than others. It seems to be worse with zooms and even worse with wider range tele zooms. For instance moving my had in front of my Pentax 10-17mm will cause it to focus but just powering on the camera with the Bigma attached will cause it to hunt for focus. I tried changing focus modes and changing the focus options in the menus and it still does the same thing (in Manual focus the red focus light will keep coming on as you move the camera around) I tried the lenses (with the exception of the Tokina) on my K10D and they work just fine.

I will be contacting Pentax service today, but I guess my question is could this have been caused by the contacts on the older Tokina lens? My camera may have been doing this for awhile and I just never noticed it because most of my other lenses are much quieter than the Tokina and many of the wider angle lenses hardly do it at all due to the larger depth of field. I have held off attaching the Tokinia to my K10D just in case.

Steve
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Old Oct 1, 2010, 11:14 AM   #2
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Steve,

One thing I would check would be to make sure that the focus is not set to the "continuous" mode. While I know that AF is supposed to operate only when the shutter button is pressed, it may be good to eliminate this as an issue before contacting Pentax.
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Old Oct 1, 2010, 11:53 AM   #3
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That was my first thought, but it does the same thing in continuous as well as single shot. I also just noticed that every minute or so the LCD display on the top of the camera will come on and the camera will focus, even with it sitting on the desk next to my computer. I'm thinking that it's a short of some sort, I'm just hoping that it wasn't caused by the contacts from one of my older lenses.
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Old Oct 1, 2010, 12:13 PM   #4
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Perhaps the shutter release is shorted on the half press. Do you have a battery grip on your camera? If that shutter release is set to on and being pressed it might be doing it too.
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Old Oct 1, 2010, 3:59 PM   #5
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Looks like you've already tried to move the focus lever around - once or twice mine didn't really go all the way to single shot or I slightly moved it or something and it would be continually focusing with half press. If you aren't using a grip I'd send it in because it does sound like a short of some sort. Have you tried cleaning the contacts? That's always a good idea if things are strange, but not sure it would help. I wouldn't think that just using a lens would cause your camera to act that crazy though.
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Old Oct 1, 2010, 5:45 PM   #6
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One thing to try is to switch AF actuation to the AF button and deactivate AF on the half press of the shutter. If this works as it's supposed to, then I'd say that this narrows the problem to the half press contacts in the shutter.

The shutter is very sensitive, so I'd make sure there's no debris that might be causing it to hang in the half press position. It wouldn't take much. . .

Scott
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Old Oct 1, 2010, 9:33 PM   #7
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I think you should write to Pentax.

They will quickly add it as a feature !
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Old Oct 1, 2010, 10:41 PM   #8
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Well I feel stupid, feel free to ridicule me as much as you want.

Thanks everybody, I think the problem was the grip (Pentax tech didn't even think of that one when I was on the phone with them). The shutter on the grip wasn't completely in the 'Off' position (must have moved when I took it out of the holster case yesterday) my hands are pretty big and the corner of the camera grip rests in the palm of my hand. The Tokina, as well as the Bigma, are heavier lenses and push harder into my hand. When the camera was sitting on my desk the edge of the grip was up against a magazine which probably accounts for that one. The thing is while cleaning contacts on the mount, lenses, etc. last night I even took the grip off to check those contacts and didn't notice the button wasn't completely in the 'Off' position, [so now I've probably messed something else up by taking the grip off and putting it on while it was turned on ].

I'm going out tomorrow and put it through an extensive test, but I have a feeling that it is solved. At least I don't have to make a trip to Fedex on Monday.

Thanks again,
Steve
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Old Oct 1, 2010, 10:51 PM   #9
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im really glad you figured it out, it stinks having a camera in service!!
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Old Oct 2, 2010, 8:36 PM   #10
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I'm glad you figured out the problem. As I read through this thread, I had no idea what might have caused it.
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