I stumbled across this FOV calculator which shows how an astro object will look - size wise - for a given telescope and eyepiece (for visual) Or telescope and camera (for imaging).
You can choose from a list of messier, Caldwell, solar system for the astro targets. The list of telescopes, cameras ( dslr and ccd) and eyepieces looks quite comprehensive. There are a number of FOV calculators out there but I found this useful as it gives me a visual aid as oppose to trying to imagine what one degree and arc seconds look like. Good for a newbie like me who have no perception of how an object will look for a given telescope/eyepiece/camera combination. http://www.12dstring.me.uk/fov.htm