Cheers Don... I was about 15 feet from the dancers, and about 30 feet from the speakers.

Thanks, I'll take a look. It might not even be as much as a tenth - it's too small for me to make a sensible estimate. I've watched it a couple of times more now, and I'm not as convinced now that I'm seeing what I thought I was seeing. It just seems so unlikely...

Has anyone come across a situation where the audio and video are slightly out of sync?

I filmed a post-dance-class demo last night, and the couple teaching are both extremely good dancers (Argentine Tango, if anyone's interested), and it's inconceivable that they would ever be out of time with the music.

I certainly didn't notice anything while I was filming, and was only watching the LCD to make sure they were in shot.

Yet on the AVI file as uploaded, the audio seems a tiny bit behind. By tiny, I mean a tenth of a second or so, and I'm not even convinced that it's a real effect. I've watched it in VLC player, and opened it in Windows Movie Maker (yes, I know.. ), and they're the same.

Anyone seen this? I was very close to the action, and the speakers, far too close for any speed-of-sound effect.

I can't show you the video, unfortunately. Not a very good video, protection of reputation and all that.

As a supplementary question, is there any free software that would let me shift the soundtrack in an AVI file by a very small amount?

I always try to be helpful

As the saying goes, 'Don't force it, get a hammer'.

You could bang the camera very hard on the desk and knock it out that way...

That makes sense. Warm Jeep, high humidity, cold lens.

Phew, I don't have to relearn all my Physical Chemistry after all

Well there's an example of a beautiful theory ruined by an ugly fact

I'm now even more curious - I'd have thought if it misted up inside while you were out, the innards must have been cooling down, and then been subjected to an increase in humidity.

Any phase-change specialists out there able to tell me what I'm missing here?

Ok, so I guess you were using the lens for a reasonable length of time outdoors (allowing the camera and lens to cool), then brought it indoors.

Then you zoomed the lens to the long end, sucking in a big gulp of warm moist air from the house. Warm air, cold surface, hence condensation.

Then once the lens' internals had warmed up to room temperature, the condensation would evaporate, and would find its way out.

Nothing to worry about.

Weather sealed lenses aren't airtight, so I'd doubt very much that the weather sealing can completely prevent ingress of water droplets the size you get in mist. So weather-sealed lenses probably aren't any more protected against mist than non-weather-sealed lenses. That said, the fact that the air gaps are small is going to prevent most of anything getting in, sealed or not.

Secondly, the mist is only a potential problem if it adheres to the inner surfaces and then doesn't have a chance to evaporate when you bring it back indoors.

So with any lens, weather-sealed or not, you don't want to take it from a high-humidity environment to a low one, and then seal it inside a bag - leave it where the air can circulate.

Conversely, if you've been using the lens outside in very cold dry air, and then bring it into a warm, moist house, moisture from the air will condense on the lens surfaces, inside and out.

Again, the answer is to leave the camera and lens somewhere where the air can circulate - any condensation will evaporate as the gear approaches room temperature provided the air can get to it.

To prevent (most of) the condensation in the first place, put the camera in a sealed freezer bag before bringing it indoors, and then take it out once it's reached room temperature.

In practice, mist is a non-issue, as Ken says. Normal good practice (ie, don't leave lenses sealed into moist environments) is all that's needed.

I'm curious about this 70-200 range. It was common in 35mm days, but the equivalent range on APS-C is about 50-135 which we have, and it is F2.8.

So why is 70-200 the 'sports' benchmark now?