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05-13-2011, 01:07 PM   #1
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K-x aperture problem: always fully stopped down on DA lenses

Hi y'all.
I have been facing a very strange problem with my K-x. It looks like the camera is not being able to set the lens aperture.
The problem occurs only with new digital lenses (that do not have an aperture ring). I have some old M lenses, a SMCP-DA 40mm limited and SMC DA-L 18-55mm kit lens.
It started the other day when I turned on the camera at a friend's place to take some low light shots at 40mm f2.8 and the image was very dark. I tried a lot of different apertures, and all images where dark, like I was using f16 or higher. Even if I used the flash, dark images. I only get a little bit of light with ISO 12800! Or with smaller apertures and the flash on (f11 + flash, i.e), but only for close objects in the flash range.
I thought the lens could be broken, but after I switched lenses the same problem occured with the 18-55mm. I also tried all camera modes (M, Tv, Av, and all presets) but the problem persists. I switched lenses several times, and nothing.
However, with my old lenses I can shoot with the correct aperture I choose on the aperture ring.
After some trials, all I noticed is that the aperture seems to be stuck at f22 independently of what you've set on the LCD/viewfinder.
When I take a shot looking directly to the lens, the lens is fully stopped down! I can see the blades closing to the minimum aperture (f22, f32, do not know exactly), even if I set the larger aperture (f2.8 on my 40mm or 3.5 on the 18-55mm). Although the lens is always shooting with the same smaller aperture for the blades, the exif info shows the larger aperture I set on the camera (back lcd and viewfinder).
So I checked the 2 SMC DA lenses parts. Both seem to be ok. The aperture mechanical lever are working fine, moving all its course and when pressed, opening the blades to the larger apertures as it should. For the SMC-M lenses, the blades are positioned according to the aperture ring, which makes perfect sense since they are all mechanical. On the other hand, the blades on the SMC-DA lenses, which do not have an aperture ring, are always wide open, stoping down to the aperture set by the camera only after you press the shutter button.
It looks definetely like a body or electronic problem.
I tried to reset the camera settings with no success. The problem still persists.
Have anyone faced any similar problem with the K-x or maybe another camera model?
I will take the camera for service in the next weeks, as soon as I have some time to do it. I am very concerned about it, because I have been always very careful with the camera, which is like new, has no scratches and has never been dropped. I have had some bad experiences in the past after repairing services on Canon and Sony compact cameras. Hope the Pentax service guys do not disappoint me!


05-13-2011, 01:27 PM   #2
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Sounds like the lever on the camera that pushes the aperture open might be misaligned or jammed- check it first!
05-13-2011, 01:39 PM   #3
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QuoteOriginally posted by Adam Quote
Sounds like the lever on the camera that pushes the aperture open might be misaligned or jammed- check it first!
Hi Adam,
I do not have the camera with me at this moment, but If I am not wrong the lever on the camera is all the way up and I did not try to force it down.
With the camera off and open, should this lever move if I try to move it down? As I can remember, it is stucked in the upper position.
Thanks for the reply.
11-03-2011, 01:45 PM   #4
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Let's update this thread:

QuoteOriginally posted by amrocha Quote
If I am not wrong the lever on the camera is all the way up
Actually, the lever was in its correct position, in the middle.

After a couple of months in the repair shop, the technician tells me the problem is at the aperture control circuit. He is an experienced Pentax technician and he says it is the first camera he finds with this problem. Unfortunately, he does not have a spare circuit and we would need to import it, which would cost a lot.
Therefore I will keep the camera as it is, only using lenses that have an aperture control ring.
And later next year, when I have the chance, I will buy a K-r or a K-5, or even a newer model.


Last edited by amrocha; 11-10-2011 at 04:12 AM.
11-03-2011, 03:47 PM   #5
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amrocha,

Please read these two threads. They may help.

Thread 1

Thread 2
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