 Many of these targets are small and require long focal lengths, which can push the focal ratio far above 5.Combined, these parameters make these targets extremely difficult to capture with film; exposures from 30 minutes to well over an hour are typical.As a typical example, capturing an image of the Andromeda Galaxy at 4 will take about 30 minutes; to get the same density at 8 would require an exposure of about 200 minutes.