WAAT : The Weekly Ask Anything Thread, week of 15 Jan - 21 Jan

I'll compare within the same price range, say a 200mm F/4 astrograph newtonian (like the Skywatcher/Orion) to a 80mm F7.5 doublet APO refractor

Refractors

(+) lightweight, not so taxing on the mount
(+) low focal length, doesn't require as good tracking
(+) very resilient, does not require collimation
(+) lower focal ratio makes focusing easier
(+) very sharp and contrasty
(-) requires a field flattener for optimal performance, though it isn't bad without
(-) small aperture, imaging takes significantly more time and very faint details can be overpowered by noise due to longer exposure time (-) front element is more exposed to dew

Reflector

(+) big aperture, images take less time and can pick-up more faint details
(+) primary mirror is less exposed to dew
(-) requires good colimation, can be knocked out of colimation when moving it around by a bump
(-) requires a coma corrector for optimal performance, which if left uncorrected is somewhat more bothersome than field curvature from a refractor
(-) slightly longer focal length, will require slightly better tracking
(-) heavier, requires a solid and more expensive mount (for a 200mm F/4 a Skywatcher HEQ5 would probably be a necessity)
(-) low focal ratio makes the depth of focus very thin, meaning focus needs to be very prices and alignment in the focuser-corrector-extender-camera chain needs to be solid with no sag (don't neglect this - most people using newts end up upgrading their focusers to much more solid and expensive units)

As you can see, there are a lot more ease-of-use type advantages to refractors, that's why they're such a good fit for beginners. In the end though the key factor is aperture, all the other factors are solvable, just make sure if you buy a newtonian that you are prepared to deal with them.

/r/astrophotography Thread Parent