Follow Focus unit gear ratios

[Kevin Kelly]

Most cinema lenses have about a 300 degree rotation from near focus to far focus. Typically, follow focus units for these lenses are geared 2:1. So, does a normal setup like this mean a 150 degree rotation on the follow focus wheel?

 

I've noticed that some follow focus units have a 1:1 gear ratio, to be used with dslr and still lenses. If you have a lens with a 180 degree focus range, and use a 1:1 gear ratio follow focus, does that mean you get a 180 degree rotation on the follow focus wheel?

 

In general, if the follow focus is matched to the lens you are using, are there any advantages or disadvantages to each combo?

 

Kevin

 

 

[Mark Dunn]

The FF unit can't know how many teeth the lens FF ring has.

So the ratio must be between the knob and the gear which drives the lens ring.