Shorten a Focus Throw

[Derek Doublin]

Shooting with the Tokina Cinema Vista lenses which have a long focus throw of 300 degrees. Can't I shorten the focus throw using a smaller gear on a follow focus? I'd like to make the focus throw easier for a single operator, I'm just not sure which gear I should be considering for this purpose. The lens itself has a 0.8 MOD and the ring has a 32 Pitch.

 

[Phil Holland]

Good companies with quality follow focus units usually provide their standard 0.8 mod gears and both larger and smaller gears with more/less teeth to adjust speed transmission ratio. OR they provide a different ratio knob.

To give you some perspective on the right way to do it. Arri provides 4X gear ratios for 0.8 modulus:

- 35 teeth
- 43 teeth
- 64 teeth

Bright Tangerine provides:
- 35 teeth
- 43 teeth

Chrosziel, Wooden Camera, OConnor, etc. all have gears for different ratios as well.

 

[Jacek Zakowicz]

Shooting with the Tokina Cinema Vista lenses which have a long focus throw of 300 degrees. Can't I shorten the focus throw using a smaller gear on a follow focus? I'd like to make the focus throw easier for a single operator, I'm just not sure which gear I should be considering for this purpose. The lens itself has a 0.8 MOD and the ring has a 32 Pitch.

larger FF gear would help you. Smaller will make it worse for you

 

[Derek Doublin]

Good companies with quality follow focus units usually provide their standard 0.8 mod gears and both larger and smaller gears with more/less teeth to adjust speed transmission ratio. OR they provide a different ratio knob.

To give you some perspective on the right way to do it. Arri provides 4X gear ratios for 0.8 modulus:

- 35 teeth
- 43 teeth
- 64 teeth

Bright Tangerine provides:
- 35 teeth
- 43 teeth

Chrosziel, Wooden Camera, OConnor, etc. all have gears for different ratios as well.

Great info Phil, thanks.

larger FF gear would help you. Smaller will make it worse for you

Yep, makes sense.
I imagine more teeth on a larger gear would be the best arrangement.

 

[Jacek Zakowicz]

number of teeth is determined by the pitch and diameter. Just looks for the most teeth - that will be the largest gear

 

[Derek Doublin]

number of teeth is determined by the pitch and diameter. Just looks for the most teeth - that will be the largest gear

Copy!

 

[Derek Doublin]

Just curious what can I expect trying to shorten a focus pull from a lens with a 360 degree focus throw? Can I get it down to a 180 degree throw or less? Or will the differences be rather subtle with the larger gears?

 

[Jacek Zakowicz]

double the number of teeth on the follow focus gear will half the amount of rotation of the knob

 

[Greg M]

also if you are using the tiny Tilta or similar FF, its just too small for a Cinema lens. They are designed for still lenses, and dont even work well with those. Your best bet is investing in a proper follow focus first.

 

[Robert Hofmeyr]

Somewhat similar question re electronic follow focusses: do any of them allow you to make the ratio variable? For example, so you can make 5 degrees of turn correspond to 1m change in focus throughout the range. I find with my stills telephoto zooms, when the subject is far away, tiny turns of the focus ring make a big difference, but when it is close I have to turn a lot to make a difference.

 

[Derek Doublin]

also if you are using the tiny Tilta or similar FF, its just too small for a Cinema lens. They are designed for still lenses, and dont even work well with those. Your best bet is investing in a proper follow focus first.

Do you think the Arri MFF-2 Mini Follow Focus would slip on a big cinema lens like the Tokina Vistas? To me, it looks like it's the size of the Tilta.