Webcam shutter speed

The shutter speed indicated by the Philips control panel is not the true shutter speed of the camera. I measured the true shutter speeds with my Philips PM 3232 oscilloscope and obtained the results in the tables below. I tested for three different frame/second settings, 6 different shutter speeds (and 3 frame sizes). I did not test all combinations of shutter speed and fps setting, but only the most relevant combinations for astronomical use.
For planetary imaging 5 and 10 fps are mostly used, with a shutter speed of 1/25 to 1/100. The Moon (and Sun) usually require some faster shutter speeds.

This is how the testing goes: capturing the trace of the oscilloscope with the webcam. When you know the time/division you can calculate the shutter speed. In this case the time/div was 50ms, so the exposure is 200ms.

The first table is for the ToUcam Pro PCVC740 and ToUcam Pro II PCVC840, tested both with the ToUcam Pro PCVC740 cdrom driver, version 1.0. Because both cameras use the same driver, the results are also the same (not very surprising).

The ToUcam is a very strange beast when it comes to accurate shutter speeds according the the driver setting. Only at 15 fps and 1/33 and 1/50 seconds these speeds are accurate.

The second table is for a Vesta 675. Here I also tested the auto-mode, as this gives another shutter speed choice. See for an explanation of the use of the auto mode this page.

As seen in this table the Vesta responds almost to every shutter speed the way it should. At least it is very close to the values, except for the 1/25 and the 1/500 second setting at 5 fps.

I also tested the behaviour of the shutter speed with a different frame size, like 352x288 or 320x240, but there were no differences with the 640x480 frames. Therefore I do not list these tables.