HDV Flicker caused by Strobe light, Help needed :)

[Steven Wyatt]

Hello,

 

I was working on a music video as a gaffer as part of my course, and we wanted to shoot a scene in a nightclub, utilising a strobe light. We were shooting on HDV, through a Movietube LT with Nikon Nikkor lenses. We shot with 9db gain, at 1/25th Shutter and used a Zenin 400w Strobe light. You could desribe the effect as a scrolling scan line which went from top to bottom gradually.

 

Does any body know what this is and or how to fix it if not prevent it from happening again? Comments and suggestions appreciated.

 

Regards,

Steven

[Michael Nash]

It's caused by the "rolling shutter" design of CMOS sensors which scan the image one line at a time, from top to bottom. You can read more about it here.

 

Basically the only way around it is to make sure that the flash duration is longer than the shutterspeed.

[Michael Collier]

sounds like a phase issue. You say you used a 1/25th shutter, is this on a PAL camera (shot at 25fps) if so then your running a 360deg shutter. What rate did you run the strobe at? My guess is the camera was a CMOS, complete in rolling shutter wonder, and your strobe was close enough to the frame rate that it began to phase in and out. Similar to when you shoot a computer monitor without CLS shutter on (or any other non-sony equivalent sync shutter scheme)

 

I guess we need to know camera setting and strobe setting to know for sure. I would imagine you should have seen it in the viewfinder, and could have adjusted either the shutter or the strobe rate to correct it, doesn't sound like something that can be corrected in post tho.

[Steven Wyatt]

I don;t know much about the settings but we shot on the V1