|My testlab to measure shutter speeds.|
To "calibrate" the speed of the disc I photographed it with my digital camera set on 1/10, 1/20 and so on. Calculations showed how fast the disc had spinned. Also I filmed the rotating disc and viewed it in slow motion, counting the turns per second.
I am still trying to find out the film speed of the early films. There are some original film boxes with the text "30 sensitometer", but I do not know which scale was used. Maybe it is the Warnerke scale, but even if it is, I cannot compare the Warnerke scale to a ASA/ISO or DIN scale. Even a conversion to a Scheiner or H&D scale would be useful, as long as I know which version of these scales are used. There are US, UK and German versions of these scales.
My own conclusion based on shutter speeds and standard aperture settings is that film speed around 1900 was about 25 ISO.
What else did I do? Well, I bought two nice photographs to go with my cameras. The first one is a scene made with a No. 4A Folding Pocket Kodak. Yes, it says Folding on the back of the card. It must be a mistake of the printer, because the 4A was called Folding Kodak. It was and is way to large for any Pocket.
The second photo is a beautiful shot of an early aeroplane. It was made with a No. 3A Special Kodak. I do have that camera model, but I display the photo with my much more interesting Military version of the No. 3A Autographic Kodak Special. Only 100 of these cameras were made in 1916 for the US Signal Corps.