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06-18-2012, 05:47 PM   #1
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F-- ?

Recently, my K7 keeps getting stuck on F--. i.e it can not sense/set the aperture of lenses. It happens most with DA LTD 15m but also with most of my other lenses. So it's the body not the lenses.

I have cleaned up the terminals with an eraser (on the body and lenses) and it is better but they were not really dirty.

Any ideas on why this happens and how to fix it permanently. Is one of the contacts specifically for F stop?

mike

06-18-2012, 06:21 PM - 1 Like   #2
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Tighten the screws on the lens mount. I thought I had a bad 500mm until a couple turns of a little screwdriver. Tighten the mount on the body and lenses affected to make sure.
06-18-2012, 06:29 PM   #3
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QuoteOriginally posted by manacho2005 Quote
Tighten the screws on the lens mount. I thought I had a bad 500mm until a couple turns of a little screwdriver. Tighten the mount on the body and lenses affected to make sure.
I had the same problem with DA* 55- it would display F-- and aperture could not be changed from 1.4, AF didn't work either.

I did exactly this and it turned out to be the fix.
06-18-2012, 07:07 PM   #4
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Cheers. Will have a look at it later (at home).

mike

06-19-2012, 10:23 AM   #5
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Here is why a loose mount causes the problem:

Recent/current Pentax bodies will display the aperture only if the 'A' pin is shorted. If you look at the mount on the body, you will see that this pin (3rd from the left) is indented unlike all the other contact pins that stick out. On a Pentax-A lens with an aperture ring, the 'A' setting causes the corresponding contact pin to be extended and manually specifying an f/stop on the lens causes the pin to be retracted. DA lens always have the 'A' pin extended. A mount that is not snug makes the distance to short the 'A' pin all the longer.
06-19-2012, 03:18 PM   #6
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Checked the lenses and mount. The lenses were all tight. The mount on the body wasn't really loose. I could tighten each screw about half a turn.

With the DA 15 mounted it all works correctly except if I twist the lens a little... without too much force it still displays F--. Having a close look at the mount my guess is that it is just a tiny bit off centre. That is, I wouldn't say the pins are all exactly centered in their holes.

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06-19-2012, 03:46 PM   #7
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The CHEAP FIX -- Figure out which direction you need to turn the lenses -- THINK ABOUT IT TWICE -- then open up the latching notch on the lenses ON THE CORRECT SIDE with a scraper or Dremel tool about 1/3 rd of a fingernail's worth.

It ain't pretty or elegant but it does work if the body's at fault. An', yeah, I've personally done that.

H2
06-19-2012, 04:17 PM   #8
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I don't know if that will help. IMO the problem is that the lens can twist a little on the mount. Opening it up will just make it twist more... that is, have more free play. Surely that will make it worse.

It does work OK now, BUT i can force it a little and make it display F--.

06-19-2012, 08:15 PM   #9
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Does your lens make a definite "click" when mounted or is it muffled. If muffled, the lens release button might need lube. My P30 had a rusty lens release, and caused a similar problem.
06-20-2012, 03:53 PM   #10
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There is a nice sharp click.

I tightened the lens mouth as much as i could. There is less than a mm of play in the mounted lens now. No more F-- unless i really push the lens (which i won't )

mike
06-20-2012, 08:40 PM   #11
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Awesome, click away with that da15!
06-22-2012, 09:05 PM   #12
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I may as well just super glue that 15 LTD on there. I have barely touched any of my other lenses in12months...
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