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Carl Craver

Detecting Flickering lights in prep before shooting

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Does anyone find light flickering tedious to fix on set? It's often checked using an in-camera test during a shoot which can slow down production. Is there any reliable & convenient way to detect light flickering given a target fps & shutter during prep instead?

I've heard bad stories about the in-camera test failing/forgotten which caused re-shoots. Have you thought about the problem? What's your solution?

Thanks

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Hi Carl

One solution is to use a spectrophotometer with flicker measurement.

Gossen Mavospec Base can do it. UPRTEK has one too.

https://gossen-photo.de/en/mavospec-base/

Having flicker main frequency evaluation (neglecting harmonics influence), you can choose most secure framerates and shutter speeds.

Best regards

***

Yann Cainjo

Photographer & Gaffer

Paris, France

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Hold your cellphone in camera mode really close to the light source, so it is forced to use very fast shutter timing to control exposure. The result will be a whitish screen, but if there's dark bands in it, you're likely to see a flicker problem.

I wrote about this trick in more detail here.

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On 5/31/2019 at 1:35 AM, Carl Craver said:

Does anyone find light flickering tedious to fix on set? It's often checked using an in-camera test during a shoot which can slow down production. Is there any reliable & convenient way to detect light flickering given a target fps & shutter during prep instead?

I've heard bad stories about the in-camera test failing/forgotten which caused re-shoots. Have you thought about the problem? What's your solution?

Thanks

Shooting on Digital ,I think the only safe way is to shoot a test before hand .. or just shoot off a quick shot and play back.. doesn't take that long.. and certainly is quicker than a re shoot .. I do for any HFR shot.. takes seconds and can save arse big time..  there are quite a few apps on line for "safe" frame rates etc.. I use FLICKERfree.. 

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Also worth noting that it's a good idea to look at the results on a waveform monitor, not just by eye. Problems that are hard to see by eye may become more obvious in grading or in other viewing circumstances - it's easy to miss things in a tiny display on location that will become objectionable on a bigger screen in the dark.

It's much more obvious on a waveform.

Also, apps can be misleading, not because the app is wrong but because it's becoming increasingly difficult to trust mathematical calculations for this stuff because almost no new lighting, in 2019, actually runs at mains frequency. The electronic drivers in LEDs and many gas discharge lights (including fluorescent tubes, ceramic metal halide, and others) tend to run things at higher frequences, or at any frequency which was convenient to the designer. It's dangerous to predict. The cellphone test can tell you if there is likely to be a problem, but as Robin says, only a full camera test can confirm that there isn't.

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if you have another camera and onboard monitor with scopes you can keep with you on prep you can try to catch the flicker on the waveform monitor. Hold the camera very still or on a tripod and keep the waveform full screen so that you can see it better... you can probably catch most of the flicker by looking for unusual shadow activity (lows "jumping" up and down in a steady rhythm etc.)

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On 5/31/2019 at 12:07 PM, Phil Rhodes said:

Hold your cellphone in camera mode really close to the light source, so it is forced to use very fast shutter timing to control exposure. The result will be a whitish screen, but if there's dark bands in it, you're likely to see a flicker problem.

I wrote about this trick in more detail here.

Great idea. I can imagine turning this "ad-hoc" trick into a standalone app which can visually detect flicker similar to an in-camera test. Coupled it with @aapo lettinen's waveform-view suggestion and @Robin R Probyn's FLICKERfree calculator, would it be worth a digital download on the app/android store for what, $100? I've pitched this to my programmer friend and he's started work on it on his downtime. Anyone interested to keep in touch about this?

On 5/31/2019 at 6:43 AM, Yann Cainjo said:

Gossen Mavospec Base can do it. UPRTEK has one too.

https://gossen-photo.de/en/mavospec-base/

Hi Yann, which of these do you prefer and which features do you mainly use? I'm interested in picking one up, which do you suggest?

 

On 5/31/2019 at 10:58 PM, Robin R Probyn said:

Shooting on Digital ,I think the only safe way is to shoot a test before hand .. 

I've rented expensive Phantoms before, only to discover nearly every single light on set flickers when shooting at higher than 120fps, delaying the production. It's not always available for a test shot when it's actually convenient to check. But nothing can substitute an in camera test, yeah... unless you playback in real time which might sync with the problematic light 🙂 

Thoughts about creating an app?

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1 hour ago, Carl Craver said:

Great idea. I can imagine turning this "ad-hoc" trick into a standalone app which can visually detect flicker similar to an in-camera test. Coupled it with @aapo lettinen's waveform-view suggestion and @Robin R Probyn's FLICKERfree calculator, would it be worth a digital download on the app/android store for what, $100? I've pitched this to my programmer friend and he's started work on it on his downtime. Anyone interested to keep in touch about this?

Hi Yann, which of these do you prefer and which features do you mainly use? I'm interested in picking one up, which do you suggest?

 

I've rented expensive Phantoms before, only to discover nearly every single light on set flickers when shooting at higher than 120fps, delaying the production. It's not always available for a test shot when it's actually convenient to check. But nothing can substitute an in camera test, yeah... unless you playback in real time which might sync with the problematic light 🙂 

Thoughts about creating an app?

Yeah I very rarely get to shoot a test before the shoot day .. HFR is the killer for me.. as of course you only see it on playback ..but Im rarely over 120.. so easy to do a quick test.. Phantoms yeah thats a different league .. 

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Hi Carl

Regarding spectrophotometers & flicker meters I personnaly prefer Gossen Mavospec Base ergonomy, more on-set use oriented and quicker to use.

UPRTEK are also accurate spectrophotometers (same accuracy than Gossen spectrophotometer), but more laboratory and industrial production oriented.

I mainly check flicker main frequency, for safe shutter speed and frame rate calculations, flicker percent et flicker waveform to estimate if flicker amount is high or low.

Hope it helps...

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