Has anyone tried it ? How is the result ? Which keying software did you then use ? Any tips ? Thanks !

Yes, I've done it many times now with the HD100, but I recommend digitizing to ProRes or DVCPRO 50/100 for keying jobs. You can check out a few spots I did earlier this year for a local grade school.
http://www.ethreemedia.com/bss

The footage in these compressed clips was digitized as DVCPRO 100, and then keyed in After Effects using Keylight. I'd probably do this job in SD now, using my Kona LH to downconvert to ProRes 422. It would save a ton of space on a larger job, and it's probably a lot faster to render. I'd also consider keying right inside FCP now, using the Boris Chroma Keyer and the 422 antialiasing filter.

The old thread about those spots can be seen here:
http://www.dvinfo.net/conf/showthread.php?t=85526

Convert the HDV footage to a better codec, I use SheerVideo (http://www.bitjazz.com), and load it in AfterEffects Pro. Use Keylight and do final color correction with Color Finesse and you'll get very nice results.

Has anyone tried it ? How is the result ? Which keying software did you then use ? Any tips ? Thanks !

If you goto www.petros.com you can see some TV spots I did with a 110U in which I bluescreened some food items. Of course, doing a person would be much hard consider you would have to key hair. Make sure you convert the HDV into something like Sheer, or another codec that supports 4:2:2. The best program I've used for keying is AfterEffects with the Primatte plugin. Keylight does a pretty good job, but if you have a key that's not perfectly lit (or having to support objects like I did) it will be harder with keylight.

Matthew

many thanks for this info. this is a wonderful site !!!

does this mean that we should directly capture via the 251's HD-SDI to a macpro with a HD-SDI card ? rather than putting the footage on tape and capturing it later ?
does this mean that we can't use JVC's HDD ?
also, we were thinking of getting a blackmagic multibridge eclipse -
but is an internal HD-SDI card better in this case ?

thanks

If you can capture via the component out or SDI then you get better color information and that would lead to a better key. You can still capture via HD or tape. When you bring the footage inside you computer convert it to a better codec like SheerVideo to obtain the most out of your key.

why don't you try key correct pro http://www.redgiantsoftware.com/keycorrect.html , I used in an extensive project that required keying in every take and it saved my day.