Both aperture and focal length play a role in your planetary observing.  Larger aperture increases the maximum resolution of your telescope, while increased focal length increases the magnification of your telescope with a given eyepiece. There are practical limitations to both of these figures. For example, just because your telescope has a focal length of 2800mm, doesn’t necessarily mean it can support magnifying a target 700x.  The general rule of thumb is 50x of useful magnification per inch of aperture (or 2x per millimeter).  For example if you have a 10-inch aperture telescope, you will be able to magnify around 500x before your image will degrade due to atmospheric scintillation, or “seeing.”

Keeping these things in mind, if planetary viewing is what you desire most, we recommend one of our Maksutov-Cassegrain telescopes. They produce very sharp images like refractors (as they have small secondary central-obstructions) and tend to have longer focal lengths and tend to be significantly cheaper than a refractor. These will give you large apertures and long focal lengths for the least amount of money and the fewest transportation headaches. Refractors are also a good choice, although long-focal length, big-aperture refractors can be expensive and difficult to move. However, quality refractors will produce the sharpest and highest contrast views for a given aperture. Finally, Schmidt-Cassegrains are also excellent telescopes for viewing planets, as they are also very affordable and easy to move. They typically have shorter focal ratios than Maksutov-Cassegrain telescopes, but most are still long enough to provide high magnification of the planets.

Our Telescope Recommendations:

Celestron Omni 102mm Refractor (beginner)
Sky-Watcher USA Evostar 100mm Refractor (beginner)
Any of our Sky-Watcher USA Maksutov-Cassegrains (intermediate)
Any of the Celestron Schmidt-Cassegrains (intermediate/advanced)
TEC APO140ED Refractor (intermediate/advanced)

In addition to a great planetary telescope, you'll want some short focal length, high-magnification eyepieces. To calculate magnification, divide the focal length of the telescope by the focal length of the eyepiece. Remember when shopping for planetary telescope gear that you typically don't want to exceed much more than around 50x magnification for each inch of aperture of your telescope. So, if you have the Sky-Watcher 100mm Evostar refractor above (which is 4" diameter), you really don't want to go much above 4x50 = 200 power when magnifying your image. The focal length of the telescope is 900mm, so to achieve the maximum useful magnification, then a 4.5mm eyepiece would be ideal.

Our Planetary Eyepiece Recommendations:

Celestron 6mm Omni Plossl
Explore Scientific 4.7mm 82-degree eyepiece
Takahashi 6mm Abbe
TeleVue 3-6mm Nagler Zoom
TeleVue 5mm Nagler