Assertion: focal ratio | /r/HasProperty | slow
Facets:
Source sentences:
text: However, camera lenses are basically limited to focal lengths under 1000mm, because beyond that, even a 150mm diameter aperture, like on a 600mm/4.0 lens or on any 6" APO, yields a focal ratio (e.g. f8 at 1200mm focal length) that is too slow for pleasant, unguided, DSO imaging.
text: A focal ratio of 10 means this is a slow telescope.
text: Additionally, an f/number can be described as ‘fast’ or ‘slow’, and this reveals how a telescope will perform when used for astrophotography.