Replies to recent posts:

Pete : The Graveny post on that forum was one I started. The air to ground round was marked on a map but little mention has been found so far. I suspect it was for 2TAF units in 1943/4.
Eastchurch was the home of the original Armament Practice Camp (in my view) with its Leysdown range.

Thorne83: I have little on Chetton apart from a rough location at SO649908. I had it as FTC (Flying Training Command) so thanks for the Bobbington reference.

Geoff L: I suspect the camera obscura building was at RAF Aldergrove. I have plans of the Lough Neagh ranges for 1929 and 1948 but not, sadly for the period in question. Post war the range extended over the northen parts of Langford Lodge airfield but pre-war it was quite compact.
The camera obscura itself came in a portable version with a special tent to keep it dark inside. The reference to film is probably incorrect as the camaera obscura was a projected image onto a large piece of paper which an airman would mark the progress of the aircraft with a pencil using a metronome to time the marks for speed calculation.
The flash would have been a Sashalite photographic type bulb which gave a bright flash for 1/75ths of a second. With some mathematics it was possible to calculate the location of the "bomb" when it would have hit the ground - hopefully right in the middle of the camera obscura. By their nature camaera obscura could not be used for night practice.
Hope this helps