Earthshine blog

Earthshine blog

"Earthshine blog"

A blog about a system to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

PSF in a Canon 35 mm camera

Exploring the PSFPosted by Chris Flynn Oct 04, 2011 02:45PM
We decided to look at the scattered halo light around the moon in a conventional 35 mm Canon camera, out of sheer curiosity.

The field of view of the Canon of about 10 degrees across, with images of 3888x2592 pixels. There is a pincushion effect toward the very edges but otherwise the halo is well traced. 12 images starting from an exposure time of 1/2500 seconds and increasing exposure time by factors of two at each step were taken. The images were taken from Chris' back garden in Sydney on a very clear night in September 2011.








Upper plot: halo around the saturated moon (seen at left) for the five longest exposures. The uniform separation of the profiles by 0.3 (in the log) is just as expected for factors of two increase in the exposure times, so the system appears to be linear. Lower plot: log-log plot of the halo flux versus distance shows a very closely followed power law with slope ~ -1: this we call a "Toto" profile (= r^-1). The earthshine camera instead shows a "Mitzi" profile, r^-3, which is as expected for a diffraction limited telescope. A 35 mm camera has a great deal more scattered light!


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