[woodyneale]

Hi again Lads, thanks for all your brainstorming input and suggestions.

As you say JeffJS with a fixed and constant light source, the camera at a fixed ISO and focused on a fixed subject I should expect dialing in any of the various complementary f-stop/shutter-speeds to produce the same resulting exposure. Also, that should any of the modes Av, Tv and P be used then any image captured should still match those f-stop/shutter-speed combinations. Your four example shots are totally acceptable to me and would be what I’d expect.

I set my EV Comp to 0.0 when doing the tests and am running with the only firmware update Pentax provided for the K-m which was v1.10. I work with “AE-L when AF is locked” turned off. Unfortunately the K-m doesn’t have the luxury of interchangeable focus screens so she’s fitted with the original.

I considered sticky aperture blades too Snowstorm, but when more than one lens produces the same results there has to be another cause. Anyway, I’ve checked my lenses and the blades move freely on them all.

I now believe wombat2go has hit on the problem as being due to the diaphragm blades of the lens closing too slowly because of a camera body fault!

This evening I set the camera on 5 secs @ f22 and fired off a few shots with no lens attached. I noticed that the mechanism inside and to the left of the lens mount (viewing the camera from its front) which actuates the diaphragm blade lever on the lens, moved rather leisurely upwards when the shutter release button was pressed. To me this suggests the lens could stop down slowly and the shutter probably open before the diaphragm blades reach the programmed f-stop. As soon as the exposure was completed this mechanism returned far, far more rapidly to its starting position. This might explain why all my lenses produce the same result and that the more sensitive the sensor setting and/or brighter the subject the greater the risk of over-exposure. This also fits with the wider variations I saw in the histogram curves when using ISO 800.

I would also suggest that P mode tends to utilise settings in the middle of the f-stop/shutter speed choices and thereby even out the chance of overexposure.

So is this a technician job or is there something I can do?

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Last edited by woodyneale; 05-18-2011 at 11:14 AM.

[woodyneale]

I'm disappointed this thread suddenly dried up.

I've sent the camera body back to Johnson Photopia UK for them to look at.

[woodyneale]

Repair quote of £192 (incl. VAT) received from Johnson Photopia today. This is to replace the diaphragm control block and do a general check and test. To say I'm gutted is an under-statement.

When I asked SRS what the camera would be worth in part exchange against a K-5 it was valued at £125, provided I had the original box and contents! Will just have to bite the bullet for now and pray come year's end the "5" shows a more enticing price drop.

That's definitely made my K-m a back-up camera now!

[JeffJS]

Hrrrrmmm...

£192 to repair a £125 camera.... and that is only if you have the original stuff that came with it. Which means they would fix it, and resell it as a shop refurb (which is their privilege to do). Did they explain exactly what was wrong or just that the mechanism had to be replaced. I've read (here) of others having the spring come loose that connects the lever to the mechanism. Meaning to say, I hope you are getting what you are paying for. For some reason, I've never really trusted repair shops.

[woodyneale]

Hi JeffJS

I’m not actually dealing with a repair shop. Johnsons Photopia Ltd is the official 3rd party repairer for Pentax Imaging Systems in the UK so I have to trust what they tell me. Tomorrow I will be phoning them to decide what action I take and hopefully having an opportunity to establish exactly what’s gone wrong with the camera. As Pentax have perpetuated the use of an operating mechanism from film to digital cameras I must say I’m disappointed because I’ve never experienced a similar problem with my MX, MG and ME Supers.

SRS Microsystems is an authorized Pentax Pro dealer here and I’ve bought many new Pentax digital lenses from them since acquiring my K-m. Obviously the K-m is now “old” and superseded so I would not expect it to have much value.

Currently I can’t afford to shell out £900 for a new K-5. I was seriously planning on getting a K-7 until the reviews highlighted a major weakness/disappointment, which was image quality from the sensor in poor light and high sensitivity settings.

Like I said, I am really hoping near year's end the K-5 will be more in the reach of my pocket. I had toyed with the idea of a K-r but in all honesty I know I won't be satisfied. I feel keeping the K-m going is my best option; after all it's not a bad little camera.