Premium Member Jay Young Posted May 2, 2017 Premium Member Share Posted May 2, 2017 Shooting with an Arri 1.2K HMI Fresnel, looking at the scope the blue channel was waving at me. We were shooting 45-degree shutter angle, at 24 frames per second. Gaffer put the HMI on "flicker-free" but the banding still continued. We tested different frame rates and shutter angles along with setting the ballast at 60/50Hz and "Flicker-free", but it still banded. I ended up shooting at 172.8-degree shutter for that particular shot because I couldn't get the lamp to cooperate with the camera settings. Anyone else experienced this? I assume it was a wonky ballast as I have used the 1.2K Par with no issues on the same camera settings. And I can't believe the Fresnel would be all that different than the Par in the ballast department. Link to comment Share on other sites More sharing options...
Edward Lawrence Conley III Posted May 2, 2017 Share Posted May 2, 2017 Could be an old globe too. Should have a spare on set- rentals are sent out with a spare globe. Link to comment Share on other sites More sharing options...
Premium Member Jay Young Posted May 3, 2017 Author Premium Member Share Posted May 3, 2017 Could be an old globe too. Should have a spare on set- rentals are sent out with a spare globe. Lets just say that we had some green grips/electric - and when I went to the truck after wrap I discovered that all of the things I had ordered were in fact on the truck, including spare globes... AND TAPE.... they'll learn some day. Link to comment Share on other sites More sharing options...
Premium Member George Ebersole Posted May 3, 2017 Premium Member Share Posted May 3, 2017 What kind of camera were you using? Link to comment Share on other sites More sharing options...
Premium Member Jay Young Posted May 3, 2017 Author Premium Member Share Posted May 3, 2017 What kind of camera were you using? This particular shoot a Blackmagic Ursa 4.6k with the new operating system. The black shading calibration tends to affect the blue channel far more than the others, which is something I didn't really have to deal with on the 4K sensor, which is my preferred chip. The only reason I mentioned the blue channel is that was being affected most by the HMI flicker. It would calm down after re-calibration on the black shading, but still was visible. I ended up just shooting those sequences at 180-degree shutter, which solved the issue. Link to comment Share on other sites More sharing options...
Premium Member George Ebersole Posted May 3, 2017 Premium Member Share Posted May 3, 2017 When you mentioned shutter angle I thought you were shooting film. There's an old trick that sometimes could clear up flicker by taking advantage of the cycle rate on power feed you were using. It probably won't work with digital. Link to comment Share on other sites More sharing options...
Robin R Probyn Posted May 4, 2017 Share Posted May 4, 2017 Works the same on digital doesnt it.. I can get rid of flicker using shutter with digital camera.s.. or am I missing something.. ? Link to comment Share on other sites More sharing options...
Premium Member Satsuki Murashige Posted May 4, 2017 Premium Member Share Posted May 4, 2017 Is 1/192 a flicker-free shutter speed, though? Link to comment Share on other sites More sharing options...
Robin R Probyn Posted May 4, 2017 Share Posted May 4, 2017 Dont know .. was just referring to Georges post that seemed to imply using shutter to get rid of flicker was different between a film camera and a digital one.. or actually wouldn't work with digital more precisely as far as i know they function the same way.. Ive got rid of flicker with both types using shutter the same way.. but i could be missing something?.. Link to comment Share on other sites More sharing options...
Premium Member Jay Young Posted May 4, 2017 Author Premium Member Share Posted May 4, 2017 Well I learned some things today. Mostly that 23.98 is just simply not HMI safe. One can minimize it, but 24 fps is not the same as 23.98 when it comes to power and flicker calculations. I'll just shoot at 24 from now on and let post figure it out. I don't have time on set to solve these issues trying to keep post-production happy and efficient. Link to comment Share on other sites More sharing options...
AJ Young Posted May 4, 2017 Share Posted May 4, 2017 (edited) Were you using an electric or magnetic ballast? I've never had issues at 23.98 on an electric ballast. EDIT: Was it an ARRI brand ballast? Edited May 4, 2017 by AJ Young Link to comment Share on other sites More sharing options...
Premium Member Jay Young Posted May 16, 2017 Author Premium Member Share Posted May 16, 2017 Were you using an electric or magnetic ballast? I've never had issues at 23.98 on an electric ballast. EDIT: Was it an ARRI brand ballast? I see my last post never made it for some reason... The ballast was electronic, and ARRI brand. I solved the issue this time round by renting 10k's..... I have nothing but problems out of HMI's - personally. Although the Joker 200/400 is nice. Link to comment Share on other sites More sharing options...
Premium Member Phil Rhodes Posted May 16, 2017 Premium Member Share Posted May 16, 2017 Some HMIs certainly do this. Even Arri ballasts, alarmingly. One would have thought that things which are that expensive would be less, er, crap, but that's life. Flicker free is a relative term, it seems. P Link to comment Share on other sites More sharing options...
Matthew Kane Posted May 16, 2017 Share Posted May 16, 2017 What was your power supply? By any chance, was it a high speed ballast? I'd be curious if the problem persisted at 1000hz. Was the flicker visible in the footage, or just on the waveform? Also, did any other fixtures exhibit the same behavior? I've never had any differing performance between 24fps and 23.98, even with magnetic ballasts, old globes, etc. If there was a long run of stingers to the ballast, line loss might have been the culprit. Or perhaps an appliance or piece of equipment with a ground fault was on the same circuit. Faulty mains wiring or malfunction at the generator can cause headaches too. Also--maybe the bulb was not fully seated? I'd love to know if you figure it out--always good to learn from other's experience rather than first hand. If the fixture was marked NFG and sent back, maybe the rental house has an idea. Link to comment Share on other sites More sharing options...
Premium Member Jay Young Posted May 16, 2017 Author Premium Member Share Posted May 16, 2017 What was your power supply? By any chance, was it a high speed ballast? I'd be curious if the problem persisted at 1000hz. Was the flicker visible in the footage, or just on the waveform? Also, did any other fixtures exhibit the same behavior? I've never had any differing performance between 24fps and 23.98, even with magnetic ballasts, old globes, etc. If there was a long run of stingers to the ballast, line loss might have been the culprit. Or perhaps an appliance or piece of equipment with a ground fault was on the same circuit. Faulty mains wiring or malfunction at the generator can cause headaches too. Also--maybe the bulb was not fully seated? I'd love to know if you figure it out--always good to learn from other's experience rather than first hand. If the fixture was marked NFG and sent back, maybe the rental house has an idea. Yes, there was visible banding at normal speed, rolling up. It was being powered off mains, and I am not positive there wasn't something else on that circuit. Who knows. I did not solve the issue with the fixture, but rather opened the shutter to 180-degrees which allowed us to continue. Link to comment Share on other sites More sharing options...
Premium Member Phil Rhodes Posted May 16, 2017 Premium Member Share Posted May 16, 2017 This winds me up. Movie industry metal halide lighting gear is very, very, very expensive. I don't care if the mains was slightly flaky. Those things are way, way too expensive to have these problems without warning you, regardless of the circumstances. P Link to comment Share on other sites More sharing options...
Matthew Kane Posted May 16, 2017 Share Posted May 16, 2017 Shame there's no way to know for sure. It'd be interesting to troubleshoot, but usually when I have these issues, there's no time for anything but swapping in a new unit or fixing it in camera like you did. It could even have been a damaged head cable I suppose. @phil, modern HMI gear can do amazing things, but not even a Ferrari works right if an important part is damaged or you're working outside the operating specs. Link to comment Share on other sites More sharing options...
Premium Member Satsuki Murashige Posted May 16, 2017 Premium Member Share Posted May 16, 2017 Well I learned some things today. Mostly that 23.98 is just simply not HMI safe. One can minimize it, but 24 fps is not the same as 23.98 when it comes to power and flicker calculations. I'll just shoot at 24 from now on and let post figure it out. I don't have time on set to solve these issues trying to keep post-production happy and efficient. Hi Jay, Since it is ultimately shutter speed and not shutter angle that is the issue with regard to flicker-free camera settings, you could also shoot with the camera in shutter speed mode and still get true 1/48 sec @ 23.98p. Shooting with a 180 degree shutter angle* @ 23.98 results in a true shutter speed of 1/47.952, which is not flicker-free. *Remember, 'shutter angle' is simulated in cameras with non-mechanical shutters. Link to comment Share on other sites More sharing options...
Premium Member Satsuki Murashige Posted May 16, 2017 Premium Member Share Posted May 16, 2017 Art Adams had a really good write up about this issue on his ProVideoCoalition blog a few years ago. I'll see if I can find it. EDIT. Here it is: https://www.provideocoalition.com/rolling-shutter-and-flickering-hmis/ Link to comment Share on other sites More sharing options...
Premium Member Jay Young Posted May 16, 2017 Author Premium Member Share Posted May 16, 2017 Art Adams had a really good write up about this issue on his ProVideoCoalition blog a few years ago. I'll see if I can find it. EDIT. Here it is: https://www.provideocoalition.com/rolling-shutter-and-flickering-hmis/ Yes. I read that a few days ago. Then I told the sound recordest we were switching to true 24. All is well! Link to comment Share on other sites More sharing options...
Premium Member Satsuki Murashige Posted May 16, 2017 Premium Member Share Posted May 16, 2017 Either way works! Link to comment Share on other sites More sharing options...
Daniel Basso Posted June 12, 2017 Share Posted June 12, 2017 Hello All... I've read the topic and responses and I feel I would be doing a disservice if I left with no reply. Although it may or may not be relative to this precisely, there was a mention of 1000hz and shutter speed and angle. I suggest perusing the following 2 links. Use for future reference. DCS hi speed flicker test info http://www.digitalcinemasociety.org/essay/saturday-night-disco-orhow-avoid-flicker-shooting-hi-frame-rates Power Gems - Phil’s white paper of hi speed shooting https://powergems.com/using-hmi-lighting-high-speed-filming-applications/ All the best, Dan / Power Gems Corp. 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