Some other planetary viewing tips
(Nothing new or original here. Some would disagree or add things. You don't have to do all these. Try the easier and less-expensive ones first. Most apply to lunar viewing too.)
Setting up and observing
- Collimate the telescope, so the coma-free (or otherwise best) spot is where the eyepiece is actually looking.
- Cool the mirror to ambient temperatures. Set up early, for cool-down time before viewing.
- Use fans on the mirror before and while observing, for two purposes:
- Speed the cooling of the mirror, and
- Fans set up to blow across the front break up the "boundary layer" of warm air on the mirror surface. (See Brian Greer's reports on fans.)
- Protect open-structure scopes from air warmed by your body or nearby pavement, and from your breath. Methods include truss shrouds, setting up with the observer downwind (if possible), setup on a lawn, or use carpet pieces or a tarp over pavement.
- Find a sweet spot of magnification. Use less if fuzzy and dull.
- For planet and lunar viewing only, have ambient light from a regular flashlight shining on paper or something (but not toward your eyes), or from non-glaring porch or landscape lights, to keep your eyes photopic between views. Don't get your eyes dark-adapted when they aren't on the eyepieces. But also avoid glare that leaves afterimages. (This might be unsociable if others are nearby observing deep-space objects!) Many prefer to observe planets last for the night.
- Choose nights of good "seeing". Obviously-twinkling stars overhead indicate poor seeing. Check the "clear sky clock" for your area. Usually late night and early morning are best times.
- Observe patiently, and wait for those moments of best seeing.
Gear
- Many enjoy binoviewing on planets. Two eyes can discern difficult details better than one. Half the light intensity on each eye is more comfortable than glaring brightness on one. After parting with a bunch of money for a good one, you might not have much left for pairs of eyepieces. Fortunately, simpler more-affordable eyepieces work better with the magnifying correctors typically provided with the binoviewer.
- Baader Planetarium's neodymium "Moon and Skyglow" filter helps color contrast, while preserving a natural appearance. It is terribly misnamed, maybe from use in early attempts at light-pollution filtration. Modern light-pollution and nebula filters are not for planets, but this one is. Other somewhat natural-color filters for planets are:
- Baader's Contrast Booster (great on Mars, same as the Moon & Skyglow with the blues and violets suppressed.)
- Televue's Mars filters
- Orion Mars filter
- Denkmeier has a new planetary filter. I've not used it or seen any reviews of it.
- Make an apodizing mask.
- A shroud (for open-structure scopes), to block body-warmed air and breath.
- Get more time per view with a tracking mount, or an equatorial platform. Lacking them, use wider-field eyepieces.
- Many observers use color filters. These do the most good with economy refractors that can't focus the whole spectrum at once, so you only need to focus the color in view. These also bring out color or albedo differences of certain planets and features, in any type of scope. They take a bit of patient experimenting, and collection-accumulation. (If I fiddle with color filters at all during a viewing session, I almost always come back to the Moon and Skyglow or Contrast Booster.)
- My experience with eccentric "stop-down" aperture masks is consistently duller planet views in any seeing, though I've had good lunar viewing with one during poor seeing.
Telescope types and design
- Planetary viewing is most demanding of optics quality. "Diffraction-limited" does not guarantee great planet viewing.
- Longer focal ratios - can be made more accurately for a given amount of effort, minimize coma; simpler eyepiece types handle it better. They also enable...
- Smaller secondary obstruction, to minimize damage to contrast. Smaller is always better; the popular rule of thumb is to avoid anything over 20% (although some great planetary scopes do go higher). Smaller secondaries gain more from apodozing too.
- Unless a totally closed-tube scope, provide ventilation and fans, to get and keep the primary's temperature close to ambient, and to blow off the boundary layer of air warmed by the primary surface.
- Large aperture maximizes contrast. The main limiting difficulty is cooling off the thick glass. Some argue that mediocre "seeing" damages large-aperture views more than small. But the case is strong that medoicre seeing damages all planet viewing, and a larger aperture continues to maximize contrast of planetary features of low intrinisic contrast, although poor seeing reduces the "bang for the buck" of a large aperture.
- Good ventilation of the primary mirror.
- Thin secondary vanes. It's not just that the amount of diffracted light is proportional to their area. When thinner, the diffracted light has a wider distribution pattern of less intensity. The configuration (straight, curved, 4 or 3, etc.) matters much less if they are thin.