Hi guys back again .... I've decided to do this at the last minute as usual and the darkest ND filter I can get at short notice is 10 stops worth. However I'm going to put a d2x on a sucker pad in my car window and try to take a 15 minute exposure at dusk as I travel along the motorway ....
Ros
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If image sharpness is not the prime criteria, you could make a projection box and take a long exposure of the dim projected image instead of taking a direct exposure. At one end of a box that will be light-tight when closed, open a hole to match one of your lenses, a fully manual one preferably. Mount it securely in place with whatever materials work from a hardware store.
Inside the box at the other end, mount a white, non-glossy screen similar to projection screen material. Some type of inkjet photo paper will probably work. Focus the box lens manually and tape the aperture and focus rings down.
Mount the camera inside the box, aimed and focused on the screen. In the extreme case, you can now set both the box lens and the camera lens to f22, and the projected image itself is dim.
A better in-line method that wouldn't have trapezoidal distortion, would be to use a translucent material for the projection screen and mount the camera on-axis behind the screen. There will be some sharpness lost by scattering within the screen.
You'll probably have to mount the whole thing on a roofrack since it'll end up being about 2 ft x 2 ft x 3 or 4 ft long.
Andy
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