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Help Determining Follow Focus Gear Ring Size (Photo Included)


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#1 Karl Lee

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Posted 10 June 2018 - 09:49 AM

Hi everyone.

 

I'd like to get a follow focus for the Canon 11.5 - 138 S16 lens that I use with my SR3, however I see that there are a few different standards for gear sizes (MOD 0.8, MOD 0.6, and so on), and that even within these standards, there are various tooth counts (MOD 0.8 w/ 35 tooth count, MOD 0.8 w/ 42 tooth count, etc.).   Is there any way for me to figure out which "MOD" standard and tooth count would be compatible with my lens?  I'm not sure if the gear rings on my lens are factory originals, or if they were added by the original owner (my lens was originally a rental which I purchased from Otto Nemenz). 

 

I've included a photo of my lens for reference.  From the photo, would anyone be able to make an educated guess as to which follow focus gear I would need for the lens?

 

Thanks to anyone who might be able to help!

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#2 Dom Jaeger

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Posted 11 June 2018 - 07:45 PM

The usual standard for cine is 0.8 Mod, which is almost certainly what a rental lens would have. The number of teeth simply refers to the gear diameter - the more teeth, the bigger the diameter and the longer the throw.

 

35 teeth is pretty standard for an Arri follow focus to use with lenses of normal diameter. If you want to have less fine control and more range with a single turn of the ff wheel (or if you have a large barrelled lens) go for a higher tooth count. 

 

You can count the teeth on your lens to get a sense of how many teeth there are from close focus to infinity, and combined with the gear ratio on your follow focus, work out what you want.


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