Thread: Strobe Effect

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  1. #1 Strobe Effect 
    Senior Member Tomas Stacewicz's Avatar
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    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: https://www.youtube.com/watch?v=T3iWvdJzx84

    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!
    https://guerillafilmsoldier.wordpress.com/

    Camera
    Blackmagic Pocket Cinema Camera
    Zenit Meteor 5-1 f/1.9 17-69mm
    LOMO 16 OKS 3-10-1 f/2.1 10 mm
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  2. #2  
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    That is probably because of the shutter angle and the light source. Try to change the shutter angle number one stop down or up and check again. It should help.
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  3. #3  
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    Shoot 25fps 180 angle or change your shutter angle when filming in 24fps.
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  4. #4  
    Senior Member Tomas Stacewicz's Avatar
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    Quote Originally Posted by froess View Post
    Shoot 25fps 180 angle or change your shutter angle when filming in 24fps.
    I guess 172.8 degrees shutter angle then...

    Thanks for the advice :-)
    https://guerillafilmsoldier.wordpress.com/

    Camera
    Blackmagic Pocket Cinema Camera
    Zenit Meteor 5-1 f/1.9 17-69mm
    LOMO 16 OKS 3-10-1 f/2.1 10 mm
    Krasnogorsk-3 pistol grip with telescopic shoulder stock
    Fancier FC-270A Tripod with FC-02H Fluid Head

    Workstation
    Windows 10 Pro
    Resolve 12.5.4.019
    ASUS X99-A
    Intel Core i7 5820K 3.3 GHz 15MB
    16GB RAM Corsair DDR4 2133MHz CL13 Vengeance
    ASUS GeForce GTX 1060 Dual OC 3GB
    Samsung 750 EVO 500GB SSD
    Seagate Desktop 2TB HDD
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  5. #5  
    Senior Member k Stark's Avatar
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    led Christmas lights tend to pulse because of the cheep power supplies
    "Senior Member"???... Really???...
    Not to be taken seriously...by anyone.....
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  6. #6  
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    Use tungsten Christmas lights instead. The frequency of an alternating current doesn't affect tungsten the same it does LED. With LED each time the current bounces per second the LED shuts off immediately causing it to blink (it blinks too fast for the eye to see). This doesn't happen to tungsten because its light comes from a burning filament. Whenever the current bounces the filament stays lit because it didn't have time to cool down, so no blinking.
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  7. #7  
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    Do use the 172.8 shutter angle at 24fps, but that still only works if the LED is at 100%, any fading in and out will cause flicker.
    If it is multicoloured RGB, then any colours except, primary and secondary, eg. RED, or RED+GREEN all at 100%, will flicker, any channel that is dimmed will cause flicker.

    Many LED christmas lights are quite powerful and you need to dim them for it to look good on camera, so I would recommend using old tungsten/halogen type lights as well.

    Alternatively get a flicker free dimmer and rewire the lights, it is handy to have a flicker free led dimmer in your light kit bag.
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  8. #8  
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    Here's a great read regarding different types of flicker and the how and why. http://www.davidsatz.com/aboutflicker_en.html
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  9. #9  
    Senior Member Tomas Stacewicz's Avatar
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    Thank's for the tips. Changing Shutter Angle to 172.8 degrees did the trick. You may see the result on this video that I uploaded to YouTube:

    https://guerillafilmsoldier.wordpress.com/

    Camera
    Blackmagic Pocket Cinema Camera
    Zenit Meteor 5-1 f/1.9 17-69mm
    LOMO 16 OKS 3-10-1 f/2.1 10 mm
    Krasnogorsk-3 pistol grip with telescopic shoulder stock
    Fancier FC-270A Tripod with FC-02H Fluid Head

    Workstation
    Windows 10 Pro
    Resolve 12.5.4.019
    ASUS X99-A
    Intel Core i7 5820K 3.3 GHz 15MB
    16GB RAM Corsair DDR4 2133MHz CL13 Vengeance
    ASUS GeForce GTX 1060 Dual OC 3GB
    Samsung 750 EVO 500GB SSD
    Seagate Desktop 2TB HDD
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