Well, fair enough, if you say so. Perhaps you can see how I interpreted your comment:
... as such, if what you actually meant was the opposite:
The thing is, I've never said that M lenses cannot be used. Of course they can. Even with the limitations of the K10D, Pentax's old lens compatibility is probably better than any other brand - even with the limitations, so why would a discussion about it put people off Pentax?

And if the limitations have effectively gone away with the newer bodies, that's even more reason for someone to go to Pentax and experiment with all kinds of optically excellent, cheap lenses.

My feeling is that honest discussion of equipment and its limitations is more likely to have a positive effect than a negative one - especially if the discussion shows that the limitations can be overcome with the older bodies, and aren't there at all with the newer ones.

Other brands' mounts have changed over the years, as I understand it, so the older lenses can't even be physically attached to their cameras in some cases.

Seriously, if a non-Pentax user has taken the trouble to come here and read the discussions, in an attempt to find out about the brand, they are likely to be a lot more careful than most to research things properly. They deserve the truth

50mm.

Always the actual focal length.

The focal length of a lens doesn't change just because the sensor happens to crop a smaller rectangle out of the image circle than a 35mm negative does.

Think about the amount the image moves because of the shake. The size of the sensor doesn't affect it, so the amount the sensor needs to be moved to compensate is not related to its size.

Well yes, this is the clearest explanation of axial CA as a cause for PF.

But note the paragraph at the end - it all gets very 'arm-waving' as soon as anyone talks about whether the sensor's contributing. I'm far from convinced that anyone understands that aspect properly.

Yes, clearly so (now!!).

But I needed you to tell me this before I put an old card in and screwed it all up

Indeed. This is the whole point. The lighting is constant, or as near constant as it needs to be; the aperture is the independent variable, and the exposure is the dependent one.

The two series of measurements are respectively the exposure that the camera (a) calculates with the lens set to A and (b) measures when stopped down with the green button.

You really do not need the ultimate in precision lighting to establish whether exposures follow the standard reciprocity law as you stop down.

If the wide open exposure is the same with the lens set to A mode and the camera to Av, as it is using the aperture ring and manual, you've already verified that the lighting is constant, to plenty enough precision for this experiment.

A milligram balance is not needed for making cakes, and nor is a micrometer needed to check your height.

Yes, my memory of the discussions at the time is that stop-down was a lot better on the Kx00D than the Kx0D.

But it was rubbish on the K10D - completely unusable, and I stopped following the debate after I got rid of my M lenses.

In a sense, Gary's right - if you have newish lenses, it's all a bit of a non-issue, since you'll just stick the aperture ring on A if it has one and forget about it.

As soon as you're really up against a budget, though, it all becomes very relevant again, and a body that can use the old lenses easily has a huge advantage.

Unless I'm misunderstanding you, this seems rather unnecessarily sarcastic.

Optically, the old K and M lenses are excellent, and incredibly cheap.

The 286/Office 2010 analogy is misleading, since new computers are cheap, unlike new lenses, which are expensive.

In a sense I agree with you - I sold all my M lenses when I discovered that the metering didn't work right on the K10D. And A-series lenses are fine, but they're quite few and far between for that very reason, as well as being much more expensive than the M ones.

The fact that K and M lenses are now convenient to use with the K-5 and other recent bodies is surely only a good thing.

I'd consider getting one again now, whereas before I certainly wouldn't.

Some lenses are, without a doubt, much worse than others for this. In my experience, the Sigma A400 F5.6 (non APO) and the Tamron 70-300 are very susceptible.

I tried to get to the bottom of this several years back, but gave up.

Axial CA (not lateral, which gives purple on one side and green on the other) is probably a large contributor when there's a clear difference between lenses (in particular the Sigma 400mm is much less bad when stopped down which is indicative of CA), but whether there's any sensor effect as various references have suggested, I have no real idea.

Well, if you wanted to get the people in the basket as well as the ground scenery, it might be quite fun.

Fisheyes aren't my thing, really, so I can't advise there.

The balloon will be going quite slowly, so you could take a whole load of shots at, say, 75mm, and build them into a synth. I reckon that would be very cool, and you'd get tons of detail as well as the panoramic aspect.

Not too wide, I'd suggest, otherwise everything will look very far away, and there'll be no close foreground to add interest as one normally looks for with extreme wide angle shots.

I use a 28-200 for all my air-to-ground stuff, and it seems to be all I need.

Here are a few (not necessarily the whole frame) to give you an idea:

Didcot power station at 50mm:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Aviation/IMGP7617-1-smsh.jpg[/IMG]

Synchrotron at Harwell at 113mm:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Misc/IMGP7615-1-smsh.jpg[/IMG]

Cerne Abbas at 38mm:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Misc/IMGP5053-1smsh.jpg[/IMG]

And at 200mm, the Homer Simpson that some wags painted next to the Cerne Abbas Giant:

[IMG]http://i162.photobucket.com/albums/t244/chris5gd/Misc/IMGP5047-1smsh.jpg[/IMG]

I took these from a height of about 2000 feet, cropping where necessary. You'll probably be lower than that, so the close stuff will be closer (vertically), and you won't be able to see quite as far horizontally.

Note the haze in the distance - long focal lengths are no good for getting good detail a long way away because of that. As you can see, 200mm can be very handy for detail that's quite close.

Let us know how you get on. At least you won't have to worry about reflections off the canopy