Telescope Basics: Aperture Size – Pros and Cons

Probably the most basic telescope parameter is aperture (no, not that one). The thing about aperture is: The size of the aperture is the area that collects light. As the night is usually quite dark, you want to gather more light.

The question is: all other things being equal, what are the "pros and cons" of smaller versus larger apertures? Usually, "More Dakka" is the way to go – most of the time there is never enough aperture. Want to see M31 (the Andromeda Galaxy) in its full glory, then a 24-inch Dobson is your friend.

However real world limits (like available funds, available space, available means of transport, or even mundane things like astronomical seeing at your observation site) usually can make smaller apertures sensible and worthwhile.

Some things are quite fine in small apertures. E.g. a cheap used 60/900 refractor is quite OK for first views of the Moon, Saturn, Jupiter or even Mars – though the number of "small telescope objects for beginners" is somewhat limited. Most things (like planetary nebula or galaxies) start to make fun in somewhat larger apertures – especially if you are an beginner.

With experience and good seeing, one can get by with smaller apertures.

	Advantage	Disadvantage
Smaller Aperture	- Less suspectable to bad seeing - Easier to manufacture - Easier to curtail aberrations - Cheaper - Lighter - (Usually) easier to handle - Faster cool down time	- Less light gathering - Less resolution
Larger Aperture	- More light gathering - More resolution	- More suspectable to bad seeing - More demanding to manufacture - More demanding to curtail aberrations - More expensive - Heavier - (Usually) more cumbersome to handle - Longer cool down time