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"Shoot the Moon"

The question this exercise answers the size of the moon at various focal lengths for a full frame and an APS-c frame camera.

The two cameras used are a Canon 5D Miii and 7D Mii. The lenses used are a Celestron 5" telescope (1250 mm focal length) and a Canon 200-400 mm lens with with a type ii and type iii doubler. Classically, Canon doesn't support stacking doublers. But they slipped with the type ii doubler which can be stacked indefinitely.

To fill the frame of an APS-c sensor requires a focal length of about 1250mm for an effective 2000 mm focal length. This was the only image taken with the Celestron telescope.

The equivelent image for a full frame sensor required 400mm plus two doublers plus the 1.4 extender. That combination creates an f / 22, 2240 mm telescope.

The APS-c sensor can go two steps further (with and without the 1.4 extender). With everything engaged, the effective focal length becomes 3584 mm more than filling the frame.