Crystal Sync Vs Variable Speed

[Kevin Desson]

Can someone please give me a difinitive description of the difference between Crystal Sync and Variable Speed.

 

i.e. if a camera shoots 24, 29.97fps Crystal and 1-50fps Variable

[Charles Haine]

"crystal synch" refers to a motor that keeps a perfect 24fps, which is necessary for synching with sound, as otherwise the sound and picture drift from each other. Called "crystal synch" because, much like a crystal controlled watch, it uses the way crystals react to electricity to time out the 24fps (maybe only the older ones did this and the name stuck, I bet newer camera's are computer controlled).

 

Now, on lower-end cameras (Arri S, IIC, Bolex), you usually have to choose, do you want a crystal motor or a variable motor? Crystal motor can be used for synch, but no slo-mo. Sometimes, you get stuck with a governor motor, which can't do slo-mo, and doesn't keep synch. However, on a modern movie camera, a range of 1-50fps is pretty normal, and when you shoot at 24fps, it is crystal 24, and synchable with sound in post.

 

That's the short run-down.

 

chuck haine

[David Mullen ASC]

You can have a camera that runs crystal sync at speeds other than 24/35, while other cameras run "wild" or just fairly constant at other speeds but crystal at 24/25, and some don't run crystal at any speed.

 

Crystal sync just means that the speed is extremely precise and constant, not an approximation.

 

For example, if a camera ran at 30 or 60 fps crystal-sync, you wouldn't have flicker problems shooting under standard 60hz gas discharge lamps / ordinary fluorescents, but if it's just a variable speed motor running at 60 fps, you'd probably get flicker from those 60 hz lamps.