I'm wondering if a small tripod (e.g. Manfrotto 190MF4 that can be collapse down to 22" or so) can be taken on board as a carry on in the US? My goal is to try HDR pictures of a cabin. Thanks!

This has been covered in the TS/S forum...there are no security regulations which prohibit a tripod of any size from being carried onboard, and I've taken my tripod on dozens of trips without a problem.

Do not mention it to the screener or ask questions - that only invites some TSA doofus to confiscate it (probably for their own personal use). If you do get hassled, call for the screening manager to intervene, and failing that, call for the airline's GSC (ground security coordinator), reminding everyone that no regulation prohibits carrying a tripod onboard.

When packing, I make sure it's well inside my bag, so no one sees any legs poking out.

Thanks a lot, bocastephen. I've visited the TS/S forum and found several informative posts there.