Intermediate speeds on Bolex speed dial

[marc]

I don't know if anyone has timed the intermediate speed settings on the Bolex speed dial but with respect to my c8, I have found that those speeds are not necessarily linear. For example, You would expect that 20 fps would be exactly halfway between 16fps and 24 fps. But I have found that 20 fps is much closer to the 24 fps mark. I have tested the marked settings for speed and they are accurate. Set at the 24 fps mark, it runs at 24 fps. So I know that it is not a matter of the spring motor being off. It looks like intermediate settings have to be trial and errored out before putting film in the camera.

[BAC]

What are you using to check the speed? I have had the same results. On some of the older cameras that don't have an 18 fps mark I have found it to be half way between 16 and 24. It would be closer to the 16 mark if it was linear. Some of this could have something to do with internal parts not being lubricated properly anymore. I have a few ways to check the speed. One way uses old film with every 18th frame marked and a stop watch. The most accurate way I use is with a photo tachometer pointed at the shutter.

[marc]

Half way between 16 and 24 is 20, so if it was linear, then exactly in between would be right. In my case, it is closer to the 24 fps mark. However, the marked settings bear out the correct speed. I am using the running time to determine the speed, since it runs for 23 seconds at 24 fps, (7 feet or 560 frames divided by 24=23.3333333) it needs to run at about 27 and 1/2-28 seconds at 20 fps.