Andrew Greenan Posted February 16, 2004 Share Posted February 16, 2004 Hi, Old topic, i'm sure. HMI's running at 50Hz, won't flicker at 25fps 180-deg shutter; nor at 24fps 172.8-deg shutter. that right? regardless of whether they're flicker-free HMI's or not. Flicker in HMI's isn't a constant strobe effect, but gives a flash frame every 24. Is that right? i'd love to, but i can't do tests on all this. Andrew Link to comment Share on other sites More sharing options...
Premium Member David Mullen ASC Posted February 16, 2004 Premium Member Share Posted February 16, 2004 Correct, assuming you are running crystal-sync 24 fps and the 50 hz power for the HMI's is within the frequency tolerances. It's not a pulse per frame, more like 2 pulses( a 50 hz HMI on a magnetic ballast is pulsing 100 times a second, I think). What causes flicker is uneven exposure where some frames get 2 pulses and some get something else like one and a half, let's say. That's why your camera has to be running crystal-sync. Link to comment Share on other sites More sharing options...
Manu Anand Posted February 16, 2004 Share Posted February 16, 2004 Dear Andrew David is correct when he says its two flashes per cycle so an HMI operating on 50 hz flashes 100 times/sec and one operating on 60 hz flashes 120 times/sec Your camera has to be crystal controlled and a frequency meter should be keeping an eye on the AC supply so that it stays as static as possible. a lil research to refresh my memory - So a sub multiple of 100 frames per second must be exposed to get a whole number of shorter than 1/100th of a second flashes and that would give you even exposure from one frame to the next.so the safe speeds that you can shoot on are therefore 100,50,33 1/3,25,20,16 2/3, 14 2/7,etc etc (dividing 100 by 1,2,3,4,5,6,7,8,9,10 etc upto 25) to give you a slowest speed of 4 fps without a flicker problem. Manu New Delhi Link to comment Share on other sites More sharing options...
Andrew Greenan Posted February 21, 2004 Author Share Posted February 21, 2004 Thanks guys, Andrew Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now