For an ongoing project, I have modified an old Brownie Hawkeye to accept a tirpod and a cable release. The images are now sharper than without these devices, but retain that 1950s feel (undoubtedly the product of the plastic lens), which is what I want. With a fixed aperture and shutter speed, though, I have trouble controlling exposure, of course and so decided to experiment with fast film and a neutral density filter. Inasmuch as traditional image quality is not my goal here, I simply bought a cheap variable neutral density filter that I intend just to hold over the lens where needed. Here's the problem, though. Although I know from the manufacturer the minimum and maximum number of stops the filter can reduce the exposure, the dial on the filter is marked simply with "minimum" and "maximum" and I'm not sure how to translate a turn of the dial to a number of stops. I don't think it's linear--that is I don't think half way between minimum and maximum is half the range of reduction on the filter--but I'm not sure if there is an easy way to estimate. Thanks in advance.