Yes I think so. Certainly better than the 5D though these things are often subjective.
What type of event are you covering? What type of connections do you need? Do you need timecode to sync multiple cameras? Is it going to a switcher?
If you are truly doing a live broadcast, then I would try to get a broadcast camera such as an XDCAM or P2 camera that has more sophisticated broadcast connections. Do a test if possible.
A major part of the appeal of the BMCC is its flat ProRes/DNX and the raw recording. For what you are talking about you are going to shooting in the video (709) color space because you can't really be broadcasting ungraded log footage. Do a test to see if you prefer the 709 BMCC image to the XDCAM image and then seriously consider which will fit best into your workflow. In a live situation, you won't have time to troubleshoot.
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Also, lens choice may be a factor. Broadcast cameras have parfocal zooms which hold focus over the zoom range. Unless you have or rent a high-end cine zoom lens for the BMCC, you may not be able to get to shots and focus as quickly as you could with a parfocal.
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For live a B4 lens would work well, but only with high quality HD optics and a 2X extender.
I've used the BMCC in live event production, in fact the very first ever live event over 100 meter fiber Thunderbolt from the BMCC, over a year ago. I did use photo zoom lenses at the time, so the disadvantage of non-parfocal optics was an issue at the time.
One thing to keep in mind, the BMCC has no genlock output, so if your switcher requires your cameras to have it, you'll have to use extra gear to make it work, or look into the ATEM switchers/sync boxes by BMD that can sync cameras that do not have genlock output.
The clean HD-SDI output is true full raster 1080 at 10-bit 4:2:2 Uncompressed REC709 or LOG (preferably the former as Matt suggested for this type of implementation). Personally, I totally prefer the BMCC over DSLR for this application in a heartbeat.
Thanks for your reply, I've tried to BMCC SDI Live output (using Carl Zeis Prime Lens CP.2) and compare with XDCAM EX1R SDI or HDMI Output, the result is XDCAM color is more dynamic and natural (XDCAM Looks more beautiful than the original).
I want to ask whether i need to do some adjustment to make BMCC Looks better for the Live output ?
For Live, I'm using BPIX Granite, Tricaster TC 860 switcher.