To find out the required inner perimeter of the gear, lay the measuring tape around the focusring of your lens and pull it tightly together. In this example the perimeter of the lens ist 246 mm.
You can measure you focus ring of the leny by using a caliper or flexible measuring tape. We recommand the measuring tape. If you don’t have one at home – just download this measuring paper:
(Make shure to print it in 100%size!):
> Measurement for Custom Follow Focus Gear <<
If you are measuring the diameter, you just have to multiply it with 3.16 to get the perimeter. You now can type in your data into the order formular.