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11-18-2010, 09:40 AM   #1
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K-x won't stop-down meter while using extension tubes?

I've been using manual lenses lately, and employ the 'Av/Exposure Compensation' button on my K-x a lot(where, on a manual lens, the camera will stop down the aperture, take a reading, and calculate a shutter speed--similar to the Green Button/DOF preview).

I tried using some extension tubes the other day. They had no contacts (and it was a fully manual lens, anyway; hence, no need), just the aperture control 'switch'. However, neither stop-down metering nor DOF preview worked with the tubes attached. John tried it on his K20d, and it works, and my K-x works fine without tubes...

Anybody have this problem or know how to resolve it?
Thanks!

11-18-2010, 09:44 AM   #2
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Are you using M mode or Av? Fully manual lenses (or tubes in your case) should work fine in M mode with the green button.
11-18-2010, 10:06 AM   #3
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For some reason the k-x treats lenses with a conductive base and ones with non-conductive one differently and won't operate the aperture with the latter when stop down metering. If the base (mount flange) of your tube set is not conductive (unlike the chromed ones of K/M lenses), then this is probably the problem.

Last edited by jolepp; 11-18-2010 at 10:44 AM.
11-18-2010, 10:36 AM   #4
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QuoteOriginally posted by MikeS Quote
I've been using manual lenses lately, and employ the 'Av/Exposure Compensation' button on my K-x a lot(where, on a manual lens, the camera will stop down the aperture, take a reading, and calculate a shutter speed--similar to the Green Button/DOF preview).

I tried using some extension tubes the other day. They had no contacts (and it was a fully manual lens, anyway; hence, no need), just the aperture control 'switch'. However, neither stop-down metering nor DOF preview worked with the tubes attached. John tried it on his K20d, and it works, and my K-x works fine without tubes...

Anybody have this problem or know how to resolve it?
Thanks!
The Exact same tubes? Do these tubes have the aperture lever?



11-18-2010, 10:43 AM   #5
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QuoteOriginally posted by Voytech Quote
Are you using M mode or Av?
I'm using M mode. It stops down normally with Av button (or Green button on DOF setting). No problems with the manual lenses, but nothing happens at all when tubes are attached.

QuoteOriginally posted by jolepp Quote
If the base (mount flange) of your tube set is not conductive
That could be it (though I don't know why). They're John's tubes, so I'll have to check with him/check them out some other time.

QuoteOriginally posted by JeffJS Quote
The Exact same tubes? Do these tubes have the aperture lever?
The exact same tubes (even with the same lens attached--either mine or his). Both work on his, neither work on mine.
11-18-2010, 10:56 AM   #6
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QuoteQuote:
The exact same tubes (even with the same lens attached--either mine or his). Both work on his, neither work on mine.
Since I've never even Seen a K-x (in person), I'm out of ideas then. Good luck figuring it out..

11-18-2010, 11:08 AM   #7
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Thanks for the help so far . I'm going to try to find out what the deal is.
11-18-2010, 11:36 AM   #8
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I'm leaning towards the short out theory above. I just verified. Camera won't stop down with nothing attached (I assume there is no other mechanism to detect lenses).

11-18-2010, 11:50 AM   #9
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Even if it doesn't stop down the k-x sets the time with M42 lenses (insulated base) with the green button (or +/-) in M-mode. For a lens that needs to be stopped down by the lever this doesn't work too well, of course. Shorting the second (from the bottom) mount pin seems to have the same effect as mounting a lens with a conductive base; an M (or K) -lens shorts them all.
11-18-2010, 12:04 PM   #10
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QuoteOriginally posted by jolepp Quote
Shorting the second (from the bottom) mount pin seems to have the same effect as mounting a lens with a conductive base
I tried this, and I'm starting to see how it works. That must be the problem. I'll have to look at the tubes again, but I'm sure that's it.

QuoteOriginally posted by jolepp Quote
k-x sets the time with M42 lenses (insulated base) with the green button
Does it do this wide open in the case of a lens that uses the aperture lever?
11-18-2010, 12:04 PM   #11
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By the way, thanks to everyone for your suggestions and help!
11-18-2010, 12:26 PM - 1 Like   #12
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QuoteOriginally posted by MikeS Quote
...
Does it do this wide open in the case of a lens that uses the aperture lever?
I think it would, if pin#2 was not shorted. In practice it seems that the lenses with the lever have a conductive (chomed) base, and the non-conductive bases go with M42 lenses such as the Takumars (there is some sort of coating on the metal bases, apparently). I know of no really convincing explanation as to why treat lenses differently based on this, though :-) Other quirks of the k-x body would seem to be raising the mirror with green button metering and also treating lenses with the aperture ring A position indicator pin shorted/not shorted (e.g. A vs. M) differently for AWB (at least).
11-18-2010, 02:49 PM   #13
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Have you tried allowing use of aperture ring in the settings menu and do it manually in M mode?
11-18-2010, 03:19 PM   #14
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In my experience with a K-x, it is the DATA pin which must be shorted for your purposes.


I use adhesive backed aluminum foil (Aluminum Duct Tape) and usually cover the whole lens base - it'll last longer & look better.

Dave
11-18-2010, 03:21 PM   #15
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QuoteOriginally posted by Rory Quote
Have you tried allowing use of aperture ring in the settings menu and do it manually in M mode?
Yes, I use mine with that setting enabled. The problem is that there's no way for me to get a light reading w/ the tubes. I plan to try using the green button to meter wide open, and then adjust from there.

Right now, using tubes on my K-x, it's like using an old Pentax K1000 with a dead battery

EDIT:
QuoteOriginally posted by newarts Quote
I use adhesive backed aluminum foil (Aluminum Duct Tape) and usually cover the whole lens base - it'll last longer & look better.
Well, I'll keep that in mind for future reference; however, the tubes are John's, so I'll try to hold off attacking his equipment with duct tape for the time being

Last edited by MikeS; 11-18-2010 at 03:28 PM.
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