Hi Brian... Wes is correct if you want to go long focal length such as into the 400+mm range. In that case, it is probably less expensive to get a good 420mm telescope (ie, Skywatcher Evostar ED 72mm). However, different target/objects in the sky could be shot using inexpensive, all-manual lenses such as the Rokinon/Samyang line of lenses. Depending on your target, you might need a 135mm... or an 85mm. Plugging these lenses into Stellarium and choosing objects in the sky, then choosing the camera and lens combo, will show you how your composition will be. Using Stellarium in this way will give you a far better idea of the focal lengths necessary (which, in the end, is really the field of view that changes).
Planets are a whole different thing. Planets need focal length. The longer, the better. Forget camera lenses for this. Actually, you can forget all relatively small telescopes too. I'd say the minimum would be a 150mm Mak-Cass but the larger you can manage (physically and financially) the better off you will be for planets.
Explore Scientific iEXOS-100 and EXOS-2GT (non-PMC)
Explore Scientific ED 102mm Refractor