RE: [APML] New All Sky Camera Images

[Aplanatic@aol.com]

This system seems to be very slow in general.  As an example:

With a 50 mm camera lens operating at f/2.8 and a reflecting sphere with a radius of 1 meter, the effective f/ratio is no faster than f/18 if the optics are set up to just image down to the horizon.  With this setup the vignetting at the horizon is well over 70%.  

In general, the f/ratio of the system is increased from that of the camera lens by the following factor:  

(1 + 2d/R) 

where R is the radius of the sphere and d is the distance from the camera lens to the nearest point on the sphere.

The best configuration seems to be a short focal length lens as close to the sphere as possible, just far enough away to catch the horizon (and be able to achieve focus) although this may produce the poorest quality images.  It's a bit complicated and I haven't worked it all out.

Dave Rowe



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