K10D Stop down metering exposure problem

I have some old M-series lenses (135 and 200mm) which I've been playing with. AFAICT their iris mechanisms are working perfectly.

In manual mode, the green button next to the shutter release is fantastic - a quick push at whatever aperture you've selected, and the camera takes a peek through the stopped down lens and sets the shutter speed.

However, I've noticed some inconsistencies in the exposure using this technique:

- with the lens wide open, the resulting shot is quite a bit over exposed
- stopped right down it's very underexposed
- at F11 it's about right.

This seems to be the case whether I use spot, centre-weighted, or multi-segment metering.

I was very careful to cover up the viewfinder completely before setting the shutter speed for a given aperture.

Anyone any ideas why this might be so? Am I doing something wrong, or have I misunderstood something?

It is well known that there appears to be a grave problem with the K10D and exposure with K/M lenses.
But normaly it is the other way round.
Wide opn it is about ok, but from about f4 it gets overexposed by about 2 stops. At least with me and what I have heard so far.

Well I've found that at F22 (with both my M-series lenses) it actually picks a shorter exposure than it does at F11.

That can't be right, can it? And unsurprisingly the resulting image is very dark indeed.

I must admit, this has come as a huge disappointment. I find it hard to see how Pentax can make a real success of the camera if the metering doesn't work properly.

Anyone have any more detailed information?

dpreview is full of threads about this.
I agree it is a disapointment. Pentax is aware of the problem, but no solution yet. It has been suggested that the kind of screen has to do with it.

For your reading pleasure, start here for example:

http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=21084008&page=1

http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=21102647&page=1

My experience is exactly the same as Chris's, with 50mm F2, 200mm F4 and Zeiss Flektogon 35mm.

It's very disapointing as all these lenses worked great with the DL2.

Ok, an update.

The exposure errors seem to be very inconsistent, and depend on how bright the scene is. For this, I used:

- 50mm PKA lens (and for the last test 135mm M series) in manual mode,
- stop down metering to set the shutter,
- viewfinder covered during the metering.
- centre-weighted metering selected
- Option 2 in Custom menu "green button in Tav and M"
- ISO 400

Test 1: Garden scene.

Results (exposures picked by camera on stop down)

F 1.7; 1/500 (Ok)
F 8; 1/8 (very over exposed)
F 22; 1/2 (quite over exposed)

Same in A mode: shutter speeds respectively 1/500, 1/30, 1/4, all Ok.

These results agree with blende8's.

Test 2: Indoor scene, low ambient light

F 1.7; 1/45 (Ok ish)
F 8; 1/5 (Ok ish)
F 22 0.7 (very under)

Same in A mode: shutter speeds respectively 1/45, 1/2, 4 sec, all Ok.

Test 3: Same indoor scene as 2; 135mm M lens

F 3.5; 1/8 (Ok ish)
F 11; 0.3s (quite under)
F 32 0.5s (very under)

Conclusions:

Which way the stop-down metering gets it wrong depends on how much ambient light there is. If there's a lot, it progressively overexposes at high F numbers. If it's a darkish scene, it progressively underexposes at higher F numbers.

Bottom line: stop down metering does not work - unless I (and presumably others) am doing something really daft.

[Rant]If my ME Super can work out the shutter speed in aperture priority, without having to stop down the lens first, why can't the K10D? [/rant]

I suppose I'll just have to stick to A-lenses and newer, and use trial and error with the M-series ones that I've had such great service with, with my ME Super and Super A.

But as I said earlier, I think having a glaring metering problem like this is going to deservedly cost Pentax a lot of credibility. Their claims about old-lens compatibility seem rather hollow to me right now.

Because the ME Super has a little metal "finger" linking the aperture ring to the body. The DSLRs all lack that linkage and so have absolutely no idea where the aperture ring physically is.

That said, I wonder if you get the same results from manual stop down metering (rather than using the green button)? What if you actually wind down the aperture by hand and meter it? Is it more accurate then?

The other thing that strikes me is that you are possibly pushing the edge of the metering when stopping down to f22... given those figures I reckon the K10D would be flashing the exposure information at you (indicating you are on the edge of accuracy). I might give it a whirl with one of the SMC-FA lenses stopped down and see what it gives...

Matt

No, this has been tested already. It's the same.
You can test this either with M42 lenses or by stopping down using the optical preview.
The metering system simply reacts strange on stopped down lenses.
Currently the preferred theory is that it has to do with the light transmission through the screen.
Two cases have been reported that the problem goes away if you use an istDs screen. Unfortunately I don't have one anymore.

my DL2 also starts to underexpose in extreme low light, the stop down meter never picks anything slower than 0.5s. However it is much more generally accurate than my 10D.

One thing I have noticed is that spot metering seems to be more accurate than centre weighted.

Just out of interest, how does one find out that 'Pentax is aware' of something like this?

Is there someone at Pentax we can talk to about what, if anything, they're doing about a problem like this?

I must say, the more I think about this, the more stunned I am... is it really conceivable that having built the green button into the camera in the first place, they really didn't stick a couple of M series lenses on the front and have a play with one of the pre-production models?

I'm not an advanced photographer by any means, but it took me all of about five minutes to notice the problem as soon as I stuck my old 135mm lens on the front.

I was in communication about this problem with Pentax Germany. I gathered that they accepted it as a problem and have reported it to Japan.
I wouldn't hold my breath though that something will change for the K10. It is quite possible that this requires changes in the hardware. Perhaps in a future model. But I am not sure.
I will keep at it. Let's wait and see ...

I am surprised by all the internet chatter on this subject. I have never had any metering issues with M or M42 lenses on an istDS. One thing to make sure of is that you stop down to meter (not sure if the auto ISO feature might also affect stop down metering) - some of the idiots out there (present company excepted) probably forget this and fire away. Unsurprisingly, they get over exposure.

I also have this K10D problem. Overexposure at small aperture and underexposure wide open when using the aperture ring. This is NOT just related to older lenses as my brand new SMC FA 35/2 makes the same measuring error when using the aperture ring.

As said above, What were Pentax thinking? They must have recognized this as the green button is there....

I only have manual SMC lenses (six) exept for the seventh, thats the 35/2 and I must say I feel cheated on, as the promo told that whatever K-mount lens there is, it would compatible with the camera. Wrong exposure in a camera made in 2006?

the issue doesn't effect the *istDS or any other *ist body, it is limited to the K10D

Exactly.

Kinda puts into perspective the now rather hollow-sounding, arm waving comments from the whingers who bang on and on and on and on about how unjustifiable it is that C/N are in the ascendant while Pentax historically have been in the relative doldrums.

It's all the salesmen's fault, of course... why wouldn't we be over the moon about this groovy slimming 'let's digitally stretch the picture, yes the punters will think that's cool' function instead of a metering system that ****ing works?

Sorry. Do I sound like I'm ranting?