Saturday, 1 June 2013

Video via towed diver

This info is mainly for my own future reference.

I have occasionally needed to record video along underwater transects (that's a scientific term for straight lines running across an area of interest). For transects of 100m or so it's OK to swim it (on scuba), but for longer distances I have been towed behind a boat. A scooter would be the best option but not within the budget.

For the video to be useable towing speeds need to be very slow. Firstly so the diver can hang on and have some depth control and secondly so the image is not moving too fast.

In the past a Panasonic Lumix LX3 has given reasonable results, but this time I tried the Nikon D7000. I wasn't using lights so did a Manual WB measurement off the sand, and that worked well. Max depth was only 4m.

Camera setup was Tokina 10-17mm at 17mm to reduce the fisheye distortion, pointing down and slightly angled forward about 1m off the bottom. 1/50th sec Shutter priority -0.3EV and ISO 400.
Here's an example of the footage captured.

Better results would be achieved with a faster shutter speed (so that single frames would be usable), say 1/125th, slower towing speed, 0EV, more distance to the bottom, say 1.5m, and/or angling the camera 45ยบ forward.

It was interesting to see thousands of Elysia viridis? slugs over the entire area we surveyed.

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