M13 Taken with MIRA's New CCD

A Photograph of M13 Taken by MIRA in 1978

Then and Now

The amazing sensitivity of CCD (charge-coupled device) cameras is well illustrated by this pair of images, both made with the MIRA 36-inch telescope. The top image is this issue's cover image, a composite of five 45-second exposures (total exposure time 3 minutes 45 seconds) on back-illuminated SITe 1024 x 1024 CCD chip. Below is an image of M13 recorded on photographic film in 1978, when the telescope was brand new; the exposure time is 76 minutes.

Manufacturers and users of CCD cameras often talk about their quantum efficiency; with a perfect detector that records the arrival of every photon striking it, quantum efficiency would be 100%. The quantum efficiency (in red light) of MIRA's new CCD is 89%; the Q.E. of film is less than 1%.