Slow motion and flicker

[Matt W.]

Shooting a bit at 700-1500 fps... Not worried since that footage will be day exteriors. Plenty of light. No flicker.

Want to shoot some interiors at high frame rates. Maybe not as high. I've heard that you need a 5k or brighter to obviate all flicker from a single tungsten source as the filament cools too much otherwise between cycles. This MIGHT be in the budget, but it also might not. 2ks would be much easier (I own two, lol). A bigger issue is that bare bulbs are part of the set dressing (potentially).

So, at what frame rate will problems begin to emerge and with what lights? 100w bulbs? 2k fresnels? Kinoflos? Electric ballast HMIs (arc wavering?).

Right now a set up might be a 2k fresnel undiffused as key, 2k through diff as fill and bare bulbs (100w per) as set dressing. Or crosslighting with 2ks through opal if that provides enough stop. Hoping to shoot at 500fps if possible. Camera will be rated at 1600 ISO. Small location, I think. Thanks.

 

[Nick Gardner]

It really comes down to the actual fixtures used, and the actual electricity in the building. Up to several hundred frames per second, you should be able to get away with most smaller tungsten units. I have gone up to 500fps with 1ks and up and had no problems, but your mileage may vary depending on how clean the power where you are is. I have shot up to 400fps with flicker free HMIs on clean power. Again, yu could have problems at 150 fps if your power is funky, your ballast is cranky or both. It pay to have a back up plan, and or test.

When I type fast I always sound like an eastern European.


Nick

 

[Matt W.]

Thanks! My guess is our 100w bare bulbs (set dressing) will flicker, but that it won't be too distracting. There's just no way around this, right? Maybe I'll look for the brightest bare bulbs available.

Power is a 6000w Honda EU genny. Tungsten fixtures don't seem to introduce harmonic resonance, so my guess is it will be good power. No chance to test much, the high speed camera is way too expensive to rent for a test shoot. I'll try to light with 1ks and 2ks.

 

[DL Fitch]

If you can use 12v/DC bulbs for the set dressing, they won't be a problem (only alternating current flickers). I recently asked the guy who runs the local lighting/grip rental shop here, and he said pretty much all of their HMI ballasts had been replaced with flicker-free versions over the past few years, so you probably won't have too much trouble finding some in the sizes you need.

 

[Ryan De Franco]

The general rule for flickering light is your fps must be equally divisible by twice the power cycle. In the good ole US of A, 60hz, 2(60)=120, so 120/5 = 24; 120/3 = 40, etc.

Shot Phantom under old fluorescents at a church today, believe it or not very doc style, ran in shot a quick test black balance and shoot the Evangelical choir communing with God... as I furiously changed fps and shutter angle between shots, the rule held up every time. On the other hand the DC suggestion sounds brilliant, you could wire a few deep cycle batteries and be just as mobile as you would with a genny, and silent.