What happens if you use the 1.7x TC with an AF lens?

Does it figure out the amount of SR automatically, or does it prompt you to tell it the way it does for a MF lens?

For teleconverters, yes, more SR is needed, since they make the lens magnify more. For extension tubes, no, more is not needed, since they don't.

The thing is, if you use a longer focal length lens (or a teleconverter, which amounts to the same thing), you get extra magnification at the same distance from the subject.

If you use extension tubes, the only reason you get extra magnification is because you move the camera closer to the subject. Focusing is the moving of the lens along its axis towards or away from where you want the image to be in focus. Extension tubes do nothing except help you move the lens further away.

It's the same with macro lenses - they're macro lenses because they allow close focusing, not because they have a different focal length than a non-macro lens.

You dial in more SR with longer focal length lenses because they magnify more than shorter focal length lenses. So for a given angular displacement of the camera (read shake), the image on the sensor moves more than with the shorter lens, and hence needs more correction.

The lens with an extension tube is not magnifying more in the same sense. The image is bigger only because you're closer - there's no extra magnification. So for a given angular displacement, the amount the image moves is the same, so needs the same correction.

The K10D doesn't recognise the focal length of A-series lenses either - you have to set the SR length manually if you switch on the camera with one attached.

In fact, can any Pentax camera detect the focal length of any manual focus lens? I thought not.. ??

I really don't understand what you find so strange. The K-5 stop-down metering with pre-A lenses works much better than it does on the K10D.

I don't see how that't not more compatible, as well as more usable, in anyone's money.

Of the three, I think the first one gives quite a decent impression of speed, with the driver leaning into the bend, and at this size at least, the kart itself is reasonably sharp.

To my eye, it would be better if the kart was angled a bit towards the camera rather than away, but I realise it's not easy. I don't have any experience at all of photographing auto racing, so I'm just giving my impression.

The bush in the foreground is just a distraction, though, I'm afraid. The 'good' blur in shots like this comes from the track and the background. Anything else just, erm, gets in the way.

This is very much the obvious conclusion.

There's a very simple experiment, of course, which would confirm it, if anyone has a suitable lens, and still uses a film camera as well as digital.

The Tamron 70-300 would be a good candidate if it doesn't vignette too badly (I can't remember if its image circle is big enough for 35mm) - take a picture of some twigs or TV aerials against a bright sky, verify that it PFs on digital, and then take the same picture on film.

If anyone's up for it, I'm more than happy to scan the neg for them on my Nikon 5000 scanner if it helps.

DA 17-70 collected! Excellent condition, you wouldn't know it wasn't new.

I'll post some pictures with a mix of 'real-world' and hopefully reasonably objective observations when I've had a chance to make friends with it.

Pleasure to meet you, Tim, many thanks.

One or other but not both. If you use both, the sensor-based SR will reintroduce what the lens IS removed.

I explained this in a bit more detail here.

It's really down to personal preference, differences in shake-removal effectiveness aside.

With lens IS, you get the image stabilised in the viewfinder.

With Sensor-based SR, you don't.

I prefer the latter, since if I can see the movement, it reminds me that I need to steady myself as far as possible first.

Another PM sent... I might have sent the first one without a subject line in my haste, and it looks like it doesn't show up.

Hmm, I did send it... but it's disappeared from my messages.

One sec, I'll send you another.

PM sent re the 17-70