Flickering

[Kathy Smith]

Hi,

I have Canon C70. I need to shoot some objects in a diorama cabinets that have some LED lights installed (cheap LED strips). The lights flicker on camera. I tried different refresh rate but that didn't help. Anyone has any idea how to mitigate the flickering?

Thanks,
Kathy

[Greg Miller]

I'm not familiar with that camera, but perhaps I can provide some helpful generic information.

*IF* the LEDs have a very inexpensive power supply, their instantaneous brightness may be related to the AC power grid frequency, which of course in US is theoretically 60 Hz. That might cause the LEDs to pulse at 120 pulses/second. So if you can shoot at exactly 60 FPS (or 30 FPS) that would eliminate the flicker, or reduce it to very slow pulsing.

However, the power grid is not an exact stable 60Hz. It may slightly speed up or slow down depending on the load on the grid at any given moment. For example, in summer, when there's a huge daytime load from air conditioners, the grid tends to slow down slightly to less than 60Hz during the day, then speeds up to slightly more than 60Hz overnight when the load is lower. (If it didn't speed up, then old-style non-digital electric clocks, with a motor dependent on power grid frequency, would get further and further behind the actual time.) It's this inaccurate frequency of the power grid that would still result in slow pulsing, rather than perfect steady exposure.

If you try shooting at 30 and/or 60 FPS and that doesn't solve the problem, then there's another possibility. Many LED dimmers work by pulsing the diodes at an adjustable rate, which is dependent on the brightness setting. In this case, in order to eliminate the pulsing, you'd need to get the diorama owner to adjust the dimmer setting until you see a steady image in your video. And since the frequency of the dimmer is not precisely regulated, it might slightly increase or decrease while you're shooting. (Current-controlled DC power supplies will not have this issue.)

[Pete Cofrancesco]

The other option is to take photos instead of video. If they're high enough resolution you can zoom and pan in editing. Those type of lights are notorious for flicker. There is software that is also designed to remove it but only works in certain situation.

[Christopher Young]

Originally Posted by Kathy Smith

Hi,

I have Canon C70. I need to shoot some objects in a diorama cabinets that have some LED lights installed (cheap LED strips). The lights flicker on camera. I tried different refresh rate but that didn't help. Anyone has any idea how to mitigate the flickering?

Thanks,
Kathy

Sorry asking, but did you try cycling through the EOS C70's enhanced Clear Scan (ECS) shutter settings?. The C70's Clear Scan covers, 24.00 Hz to 250.40 Hz in incremental steps. Within that range, you should be able to dial out the LED flicker without too much difficulty. The C70's Clear Scan was upgraded again in the C70's firmware v1.0.7.1. Page #57 of your manual. See attached pix.

I find a Clear Scan shutter essential for this type of work or when having to shoot PC screens or LED walls where you can have hum bars present. Or image tearing when you move the camera.

Chris Young

[Kathy Smith]

Originally Posted by Greg Miller

I'm not familiar with that camera, but perhaps I can provide some helpful generic information.

*IF* the LEDs have a very inexpensive power supply, their instantaneous brightness may be related to the AC power grid frequency, which of course in US is theoretically 60 Hz. That might cause the LEDs to pulse at 120 pulses/second. So if you can shoot at exactly 60 FPS (or 30 FPS) that would eliminate the flicker, or reduce it to very slow pulsing.

However, the power grid is not an exact stable 60Hz. It may slightly speed up or slow down depending on the load on the grid at any given moment. For example, in summer, when there's a huge daytime load from air conditioners, the grid tends to slow down slightly to less than 60Hz during the day, then speeds up to slightly more than 60Hz overnight when the load is lower. (If it didn't speed up, then old-style non-digital electric clocks, with a motor dependent on power grid frequency, would get further and further behind the actual time.) It's this inaccurate frequency of the power grid that would still result in slow pulsing, rather than perfect steady exposure.

If you try shooting at 30 and/or 60 FPS and that doesn't solve the problem, then there's another possibility. Many LED dimmers work by pulsing the diodes at an adjustable rate, which is dependent on the brightness setting. In this case, in order to eliminate the pulsing, you'd need to get the diorama owner to adjust the dimmer setting until you see a steady image in your video. And since the frequency of the dimmer is not precisely regulated, it might slightly increase or decrease while you're shooting. (Current-controlled DC power supplies will not have this issue.)

Thanks Greg. I tried shooting at 30 an 60fps. It didn't help. I also tried different Hz settings but that didn't help either. The only thing that worked was changing the shutter speed but I had to go so low 1/12 so then I couldn't do any camera movements.

[Kathy Smith]

Originally Posted by Pete Cofrancesco

The other option is to take photos instead of video. If they're high enough resolution you can zoom and pan in editing. Those type of lights are notorious for flicker. There is software that is also designed to remove it but only works in certain situation.

That would be my last resort

[Kathy Smith]

Originally Posted by Christopher Young

Sorry asking, but did you try cycling through the EOS C70's enhanced Clear Scan (ECS) shutter settings?. The C70's Clear Scan covers, 24.00 Hz to 250.40 Hz in incremental steps. Within that range, you should be able to dial out the LED flicker without too much difficulty. The C70's Clear Scan was upgraded again in the C70's firmware v1.0.7.1. Page #57 of your manual. See attached pix.

I find a Clear Scan shutter essential for this type of work or when having to shoot PC screens or LED walls where you can have hum bars present. Or image tearing when you move the camera.

Chris Young

Thanks Chris. I tried Clear Scan. It didn’t eliminate the problem. I had to resort to the last option on that menu list “slow”. That worked but it basically dropped the shutter to 1/12 so I couldn’t do any panning but I just didn’t move the camera, fortunately there were slowly moving objects in the diorama boxes so there is movement in those shots and they don’t look like photos.

[Christopher Young]

Wow! That's an odd one. That's so low a speed. Some strange LEDS by the sounds of it. All the same, glad you got a result you could work with :)

Chris Young.

[Greg Miller]

Originally Posted by Kathy Smith

Thanks Chris. I tried Clear Scan. It didn’t eliminate the problem. I had to resort to the last option on that menu list “slow”. That worked but it basically dropped the shutter to 1/12 so I couldn’t do any panning but I just didn’t move the camera, fortunately there were slowly moving objects in the diorama boxes so there is movement in those shots and they don’t look like photos.

It occurs to me that there may be multiple sets of strip lights, on different dimmers, pulsing at different frequencies. In that case there may be no "magic" frame rate that will give perfectly smooth exposure.

Kathy, my memory is fuzzy about this: does that camera have adjustable shutter angle (or am I thinking of something else)? If it does, the widest possible angle, combined with a slow frame rate, would produce a result closest to a long time exposure.