Sorry if I was teaching my granny to suck eggs...

But I'll be very interested to hear if the new one is better or the same.

Are you covering up the viewfinder when looking at the top LCD?

It would be interesting but not conclusive, since it would be hard to ensure that the two cameras were looking at exactly the same thing. As has been observed by others, the camera only needs to point at a slightly different part of a heterogeneous scene for the exposure to vary quite a bit.

If the scene was a big grey card, of course...

But I still think that the comparison we're looking for is between A mode and non-A (ie aperture ring) mode on the same (A-series) lens, on the same camera. Consistency across bodies is desirable, but it's a different issue.

The camera stays in manual for both, and the exposures should be the same at corresponding apertures, set for A-mode and non-A respectively at the camera and the lens.

I wouldn't go that far.

Despite the annoyances with M series lenses, and A-lenses in non-A mode, I still don't regret buying the 10.

My photographic mojo had completely evaporated after the shutter lag with my digital compact (Sony DSC T3) drove me nuts, but it's back now with the '10 and I have enough A- and later lenses to keep me at it.

It would be fab if Pentax waved a magic wand and fixed the stop-down performance with a firmware update - or indeed if it could be shown unequivocally that some bodies have the problem and some don't.

I'd still like to see some rigorous test results from those claiming that their '10 has no problems with stop-down metering.

It can't be hard, surely - slap an A lens on the front, and take a series of shots with the camera in manual and the lens in A, and then the same series with the camera in manual and the lens not in A - but use stop-down metering to pick the exposure.

If a) the exposures are the same in each series (or nearly) and b) the exposures follow the law of reciprocity as the F-number changes (because they surely do with the lens set to A), then I'll be straight down to Jessops asking for an exchange.

???

I'm not suggesting Av is superior to M for a moment. Horses for courses.

I thought I was being specific - if your objective is to pick an aperture on a pre-A lens, and set the shutter speed for "correct" exposure, the green button is quicker, and hence superior to the DOF lever method, which only gives an exposure readout - you have to then choose the exposure and set it yourself.

The thing is, as you don't get better (as in 'more correct') exposure information by using DOF preview, I suspect it's quicker to press the green button, and then dial in whatever compensation is needed to offset its error.

I haven't worked out any rules about such compensation yet, and I doubt if I will. As John says, it's all just such a faff that I'm using my A- and later lenses more and more. If I have to use either of my M lenses, it'll be for something specific, almost certainly on a tripod, where trial and error will be perfectly adequate to get the exposure right.

I didn't check this. I was testing only the difference, if any, between the metering with green button vs DOF preview.

Given that it's given the wrong exposure with green-button stop-down in much of my other testing, I would speculate that since it's the same with DOF preview, it's just as wrong, if you get my drift.

I've got some numbers describing what I did, which I need to write down properly.. I'll post them when I get the chance.

Ok, a quick empirical check of the green button/DOF preview lever gives the following results:

With:

- Camera in Manual
- A series lens but not in A (ie using aperture ring...)

... the DOF preview lever stops the lens down but does not set the shutter speed. You get an exposure readout (x stops over or under) while you hold it stopped down and you can alter the shutter speed manually until it reads "correct".

... the green button stops the lens down, AND sets the shutter speed to whatever it thinks is correct.

I could detect no difference between:

a) the shutter speed selected by the camera using the green button
b) the shutter speed selected manually, adjusting while stopped down until the readout indicates correct.

Conclusions:

1. As a means of quickly setting the shutter speed the camera thinks is correct given an aperture selected on the lens using the aperture ring, the green button is clearly superior.

2. As a means of getting a correct exposure with a non-A lens, it is no different from using the DOF preview lever.

I had a go at this - it's pretty easy to do if you're hand-holding the camera. Index finger on the shutter release, middle finger to move the lever. Easy enough to hold the lever against its spring while you push the button.

I wouldn't be surprised, though, if the tendency for camera shake was greater, owing to the increased muscle tension while holding the lever in its preview position.

More serious, though, I'd have thought, is use on a tripod, where holding the lever in the stop-down position is more likely to shake the whole assembly. Obviously the tripod will work best if you can let go while you take the shot.

Very interesting. I wasn't aware of the difference between A and pre-A lenses you describe.

However, if it accounted for the problems, would you not expect that using the same A-series lens, first in A mode, and then in non-A mode, the results would be consistent?

In my experience, they aren't. I'll post the results of my tests post-firmware 1.11 when I get a chance.

Did you actually note any change of shutter speeds at the different apertures?

According to the manual (p210), in Aperture Priority mode (Av), with A and M lenses, using the aperture ring to select the aperture, "the aperture remains open regardless of the aperture ring position".

On mine, the shutter speed indicated does not change when stopping the lens down with the aperture ring, with the camera in Av.

So if you're saying that you get correct variation of shutter speed with manually set aperture (ie using aperture ring on the lens, not setting it from the camera with the lens in A mode), then I am now officially confused.