HMI Flicker?

[Jason George]

I just shot a test with magnetic ballast HMI's and was very surprised- we went to a time base of 24fps, shot 24, 60 & 120 fps, & had to adjust shutter 'angles' for each, and were unable to capture flicker-free at 120 fps at any shutter angle- very bizarre.
Also point to note that "relative mode" in the shutter menu seems to imply "manual" , where the shutter angle may be controlled independent of the frame rate, although the term is a little awkward.This helped in as much as shooting 60 fps worked at a 45 degree shutter as well as a 90.

Whatever the case, in controlled enviornments, I would avoid magnetic ballasts altogether, use only electronic and any location with industrial lighting, including fluoros, I would test before the shoot date, before promising any frame rate and shutter angle options.

[Mike Prevette]

nevermind

[Todd Davis]

Richard,

Do you know of a universal formula for shutter angles or frame rates? IE: With electronic ballast outputting at 75 or 150Hz what would the 3 in the formula be? By the same token, I would like to know how to derive the 3 or 3.6 multiplier in situations where I have some control of frequency of the power line (generator speed control) thereby giving additional frame rate/shutter speed options.

[Richard Andrewski]

Thats a good question Todd. I would have to do a bit of research to answer how to go backwards and get those hard coded values. I'll see what I can come up with.

[Jason George]

Thanks for the replies- I am using flicker-free ballasts, (square wave) and shooting speeds up to and including 300fps. I had issues with the RED1 system at 120 ages ago and just wondered if anyone has shot with flicker free ballasts at a variety of "off" speeds and using a variety of shutter angles. The old "safe frame rates" from the film days does not translate well to the digicams of today, as far as my experience goes, flicker-free ballasts, kino flos and the like all need to be watched carefully.