Waterproof video camera with ND filter

VictorValencia wrote:

Not sure if this is the correct forum to ask in but I'm hoping someone has an idea

where I can find something similar to a backup/cctv camera with the following

features:

1) Waterproof

2) NTSC/PAL/SECAM output

3) Either has an integrated ND filter or one can be attached

4) Small (1-1.5" cube)

My application is a taxi camera for an aircraft. The camera will be viewing through

a moving prop which is why the ND filter is needed.

OK, that's a problem. As you guessed, the problem is that the electronic rolling shutter is going to give you lots of artifacts. Take a look at the 3rd image in Figure 11 in my paper Shuttering methods and the artifacts they produce -- which happens to be still photos of a spinning fan blade.

I assume you're thinking the ND filter will make the shutter speed slow enough to make the prop blur out -- I'm not sure that's a good assumption because NTSC video shutter speed never gets longer than frame time (no slower than 1/30s or 1/60s). A prop running at 2700 RPM is 45 revolutions per second, which sounds too close to NTSC framerate to blur-out completely. Cameras that produce digital video output can indeed use slower exposures because they can drop the framerate... then again, that might be unsatisfactory too due to blur from vibration of the camera and/or relative motion of the runway you're trying to view.

The good news is that the NTSC video artifacts should be somewhat randomized by the beat frequency of the scan vs. prop rotation, so it might just be annoying flicker-like artifacts rather than unusable video. NTSC backup cams are cheap; is it easy for you to just try one?

Incidentally, it might not be that hard to stick a gel ND filter in such a camera. Usually the camera is made waterproof by having the lens behind a clear plastic/glass window in the housing, so you could just stick the gel between the lens and the window.