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12-28-2008, 11:57 PM   #1
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K10D Metering Problems - Problem isolated

I posted this problem earlier, and thanks to those who responded. I realised I was stabbing in the dark a bit so I have done some extensive experimentation to attempt to isolate the issue I am having and to get some consistency in the problem. I have achieved that as described in the following.

I have achieved the same outcome using lenses DA16-45, Tamron 28-75 and Tamron 70-300. With the Sigma 70-200 f2.8II HSM mounted the Camera DOES NOT display any faults.

Fault = over exposure of captured image. I have many images shot in RAW with EXIF intact I can post if required.

Standard Settings:
ISO = Auto 100-500
WB = Auto
Metering = Multi Segment
AF Point = Auto
Focus = AF/S
Aperture Ring = Enabled (important later)

Experiment:
Lens = DA16-45

Set the camera in Green mode.


Results ISO = 100; Tv = 200; Av = 4.0. Both Av and Tv are flashing and image is over exposed.

Set the camera in Tv.


Results ISO = 200 Tv = 1,000 (Set at 1,000) Av = 4.0. No flashing and Image is OK.

Leaving in Tv and changing the shutter speed to say 500, Av stays at 4.0 (maximum aperture for the lens) Av is flashing on screen and image is over exposed.

Set the Camera to Av

Results ISO = 100 Av set at 4.0 (Maximum aperture) Tv = 320. No flashing and image is OK


Changing Av to say f = 16.0 results in a reported Av in the resultant image is = 4.0 and Tv is 30. Tv is flasing (as it should)

A theme is emerging here where any Aperture setting other than the maximum for the lens (f = 4.0 for the DA 16-45) is not being recognised.

I repeated the test using the Tamron 28-75 (Max aperture = 2.8) and 70-300 (Max aperture = 4.0) and the same outcome resulted.

Confirmation of problem:


The Tamron lenses have an aperture ring. If I set the aperture ring to any reasonable aperture (range from f=2.8 to f=16 on the 28-75) with the camera in Av, the shutter speed changes according to f-stop setting and the captured image is OK. A similar outcome is achieved using the Aperture ring on the Tamron 70-300. Remembering the DA16-45 does not have an aperture ring.

Next I disabled the aperture ring in the Custom menu. I mounted the Tamron 28-75 and the Camera was inoperable. Same outcome with the DA 16-45.

So it seems that the fault with the Camera is it is not communicating aperture values with the lenses in "A".

Strangely this fault does not occur with the Sigma 70-200 f2.8II HSM.


I have obtained some appropriate electrical contact cleaning fluid and carefully cleaned the Camera and lens contacts.

Questions:


Is there a specific contact on the Camera that communicates Aperture to the lens?

Could this be a contact problem, and perhaps the additional wieght of the Sigma ensures correct contact between the lens and the Camera??

Any other suggestions. What would you do next?

12-29-2008, 02:12 AM   #2
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It seems obvious to first check the A-pin.

Look here:
Features and Operation of the Ka Mount

The pin labeled with a * is the A-pin in fig. 2.
12-29-2008, 06:38 AM   #3
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QuoteOriginally posted by flash1100 Quote
What would you do next?
Remember that all the contacts do is tell the body what minimum and maximum aperture the lens has (if an "A" lens).
Metering is interpolated from there...
The code sequence is here:
Features and Operation of the Ka Mount
12-29-2008, 06:39 AM   #4
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QuoteOriginally posted by flash1100 Quote
The Tamron lenses have an aperture ring. If I set the aperture ring to any reasonable aperture (range from f=2.8 to f=16 on the 28-75) with the camera in Av, the shutter speed changes according to f-stop setting and the captured image is OK. A similar outcome is achieved using the Aperture ring on the Tamron 70-300. Remembering the DA16-45 does not have an aperture ring.

Next I disabled the aperture ring in the Custom menu. I mounted the Tamron 28-75 and the Camera was inoperable. Same outcome with the DA 16-45.
This is the real clue.

if you have the Use apature ring set to off, and the camera does not fire, then it is not getting confirmation that the lens is an A lens. this is the third pin from the lens locking pin on the mount. you will note it is recessed. it is supposed to be. The pins on the lens should be deep enough to contact it. if this pin, due to an error is too deep. it will produce the result you describe.

Note that in AV mode the camera should always shoot wide open, not change with apature of the lens.

If the contacts are not dirty, and cleaning them does not fix it, go to pentax and get it corrected.

12-29-2008, 06:45 AM   #5
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QuoteOriginally posted by Lowell Goudge Quote
This is the real clue.

if you have the Use apature ring set to off, and the camera does not fire, then it is not getting confirmation that the lens is an A lens. this is the third pin from the lens locking pin on the mount. you will note it is recessed. it is supposed to be. The pins on the lens should be deep enough to contact it. if this pin, due to an error is too deep. it will produce the result you describe.

Note that in AV mode the camera should always shoot wide open, not change with apature of the lens.

If the contacts are not dirty, and cleaning them does not fix it, go to pentax and get it corrected.
That contact is "slightly recessed" and is a spring/ball bearing type (at least on my camera)
12-29-2008, 07:57 AM   #6
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just out of curiosity, are you metering with the green button? I noticed recently that using the aperature ring on any of my A lenses the aperature data isn't displayed, requiring me to use the lens as if it were a M lens. If I metered with the green button no problem. If I used the shutter release halfway down, no metering, and unless the camera was in M mode the camera wouldn't fire. Perhaps I'm not understanding the problem.
12-29-2008, 09:00 PM   #7
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Original Poster
Thanks everyone for your replies. I have done some more research and isoloated the problem to the aperture actuator not working. The "give away" was that when the lens was wide open and I selected that on the Camera it worked OK, but as soon as I stopped down altho the aperture was showing a different value on the cam, the recorded image showed it wide open.

To test this, in the Custom menu set to optical preview, with the lens off look on the left hand side of the inside on the camera, the silver bar running vertically has a tab on it that slides on it and engages with the aperture lever in the lens.

When DoF preview is activated on the camera that tab moves up and down. With the lens on it engages with the lever and opens / closes the aperture blades. On mine it doesn't move.

It's going back to the shop so I'm minus a DSLR for at least a month
12-30-2008, 02:05 AM   #8
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Perhaps there is just the little spring off?
I remember a thread with photos how to fix it.

The German thread is here:
http://forum.digitalfotonetz.de/viewtopic.php?p=512464#512464

Look at the images and compare them with your camera.

01-01-2009, 02:41 AM   #9
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I have the very same problem...maybe it's this unusually colder winter

What to use to clean contacts?
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