Strobe effect

Hi!

Yesterday, I took some shots from our Christmas Tree. I only used the light coming from the electric christmas tree lights. 220 Volts, 50 Hz.

Shot with the Blackmagic Pocket Cinema Camera, CinemaDNG RAW, 24 fps, 180 degrees Shutter angle, ISO 800. I used the Zenit Meteor 5-1 lens using f/1.9 aperture and various focal lengths 17-69mm.

I experienced a quite severe strobe effect in the form of pulsating waves. Anyone that has a clue of why? My first thoughts was that it came from the christmas tree lights and the frequency it created (50 Hz).

This guy seems to confirm my suspicions:

The christmas tree shot is a part of a larger project which I shot on 24 fps. If the strobing comes from a faulty frames per second setting, what setting should I have used instead? And how to intercut it with the other footage shot on 24 fps in DaVinci Resolve?

Or is there another explanation for the strobe effect? Is there a way of working around it without changing the frame per seconds setting?

Apprecieate any advise. Thanx.

And a Merry Christmas!

I assume your lights are LEDs?

If so - there are many ways in which LED's are dimmed or have their intensity controller, one of them is to modulate them at a certain frequency. Its quite common for this frequency to be something else other than 50 or 60hz.

The issue is with your lights, not the camera.

I recommend using tungsten based lights instead.


You might never find a shutter angle which is synchronised with the lights, and doing so anyway will change the cadence of the footage and exposure too.

If your lights have several settings, see if there is a lower or higher intensity which gives you a more favourable strobe frequency,

Try 30 fps and shutter angle 108, 216 and 324.

If you're in PAL Country, I think the recommended shutter angle is 172.8 degrees shooting 24fps with 50Hz power etc. In NTSC Land the 180 degree shutter is used with 60Hz power etc.

You can search on "safe shutter angles" to find an app that will show you various settings that avoid flickering. REDuser.net has an online calculator and an app: REDtools. REDtools indicates you could use 86.4, 172.8, 259.2 degrees shutter angles. If you shoot 25fps which would be normal in PAL Country, you won't get flickering, unless the problem is the lights themselves.


Sent from my iPad using Tapatalk

First issue is using 180° shutter when shooting 24p under 50Hz lighting.


For 24p under 50Hz your "Safe Shutter Angles" are: 86.4, 172.8, 259.2°
Corresponding Shutter Speeds: 1/100, 1/50, 1/33.3 sec

This tool will help:
http://www.red.com/tools/flicker-free-video

But... as Tom pointed out many Christmas lights use LEDs that are controlled with odd frequencies.

Consumer LED lights are a disaster.

Even the same flicker speeds aren't safe. A lot of them just don't adhere to those old rules and use PWM to dim them. Seeing it a lot with exit signs too now. It's a plague at any shutter or frame rate combination. So much for standards and convention. No one cares about this stuff.

JB

Yes, they are LED's. And I cannot dim them, unfortunately. I really hate LED's; shure they are energy sawing but creates artificial light which make it hard to distringuish colours properly.

Thank's for the good tips. I will use the 172.8 shutter degree angle next time. Prefer that of changing to 25 fps.

Consumer LED lights are a disaster.

John, would you recommend against using professional LED lighting as well? Use classic Tunsten instead?

Consumer LED lights are a disaster.

John, would you recommend against using professional LED lighting as well? Use classic Tunsten instead?

A lot of the first clones of the original Lite Panels, the Chinese knock offs, would pulse when you dimmed them below about 30%.

Most of the current LED film lights seem to be OK....I don't really like LED's very much at all though as a source.

JB