I am trying to pick out an HD camcorder for use in cold weather, and the flash memory units sound like a good bet because they reduce the number of moving parts. My questions is whether they use a more aggressive compression scheme than the mini dv or hard-drive based units, because I will be recording a lot of motion and need it to come through as clearly as possible.

Any information would be appreciated.

Yes - the HD flash memory units which use AVCHD have much more aggressive compression schemes.

In most cases, the video is fine, looks good, and there is no noticable difference. Filming people moving and running around, it's fine. The problems I've seen are situations where most of the frame changes from one thing to another....

examples:
* filming a tree in high wind, where all the leaves are moving. If this tree is taking up the entire frame, then compression artifiacts can be seen. (If the tree does not take up the ENTIRE frame, or if it is not VERY windy, the scene looks fine)
* filming any scene on the other side a road. If a large truck passes by, and completely obscures the scene, the truck passing by will cause artifacts. (But taking pictures of cars on a highway from a distance (say from the 3rd floor of a building) should not cause artifacts.
* filming a HUGE amount of movement like putting the camera on the ground near the endzone of a football game. When a few players take up the entire screen falling to the ground tackling each other, there might be artifacts here (but seeing the motion from a distance such as a Televised game, it should look fine)

I was concerned about this before getting an AVCHD camcorder, but it turned out not to be a concern, and I'm very happy with my camcorder now. I should try more different types of scenes, and see how they film. (Like how does a rough ocean with large waves look? - my guess is that there would be compression artifacts on a close look at one wave, and a further look which includes 1/4 of the picture with the beach in it would be fine..... I'll see what I can film to try)

Thanks for the info--that is very helpful. I will be using it to film ski racing and football--both of which have a lot of motion.

Is there a choice for the compression level, or is there just one?

Also, since flash memory cards are likely to continue to get bigger, do you know whether the camcorder will be able to read cards that are bigger than 4 GB?

There is a choice of compression SPEED on the SD1.
* "HE" mode - 6Mbps, Variable Bit Rate
* "HN" mode - 9Mbps, Variable Bit Rate
* "HF" mode - 13 Mbps, Constant Bit Rate

I've read somewhere that the AVCHD compression algorithm needs about 22 Mbps to record 100% of the movement anywhere on the screen perfectly without any artifacts. Can anyone confirm/deny this?

How do the Sony models compare?