Backyard Voyager
Zoom Eyepieces
If you are like most people, then by the time you've chosen and ordered your frst telescope, you have also come to the realization that the spending hasn't come to an end.
How much you will spend in the future is to a great extent dependant upon the areas of astronomy that interest you the most. An aspiring astrophotographer, for example, will spend considerably more than someone who is primarily interested in observing double stars.
Planetary and close-up Lunar observation is best accomplished with a varied selection of eyepieces.
Seeing conditions are of utmost importance and can change many times over the course of an evening. In other words, comfortable observation at numerous magnification levels will be possible during most evenings when seeing conditions allow for detailed planetary observation.
Eventually you will probably want to invest in one or more of the higher end planetary eyepieces, but it would be a good idea to find out beforehand just what magnification levels could be most often used at your location.
A zoom eyepiece, as well as being a useful observation tool, would give you a good idea of what to expect, and at a reasonable price.
Back
The 50x per inch rule of thumb?Next
I don't know who came up with this one, at least as a workable rule of thumb for newcomers to astronomy. At any rate, in some quarters it is still claimed that 50x per inch of aperture will give a reasonably accurate idea of how much magnification a telescope can use. This is unrealistic, given most people's viewing conditins. It probably does hold true under the best viewing locations on earth, on the very best nights of the year. Most of us will never experience a night like that.
Images taken with Celestron C9.25" SCT and Phillips ToUcam Pro II with 3X barlow.
Unfortunately, "seeing" conditions play the biggest role of all, for both visual astronomy and astrophotography. Some nights will allow for higher magnification and greater resolved detail than other nights. These "seeing" conditions can even change within the space of an hour. In fact, conditions can fluctuate significantly even within the space of a single second, which is why the best planetary photographs are captured with webcams operating at 10 or 15 frames per second, allowing the photographer to eliminate the bad frames later on, effectively freezing those very brief instances of steady seeing.
Above is an example of seeing fluctuation. Both images of Saturn were taken from the same location within two weeks of each other, using the same telescope, barlow and camera. Both nights were cloud free and roughly the same temperature.
On the second night, after looking at the sky, I almost decided to pack it in. The stars twinkled like little strobes-- usually an ominous sign. Recalling the reasonably clear image I had taken on the earlier evening while using a 3X barlow (usually a difficult image scale with my C9.25) I decided to get a comparison shot. The results were like night and day, both in the resulting image below and at the eyepiece. On the first evening I was able to view Saturn comfortably at 300X. On the later evening, viewing at 125x wasn't even worth the effort.
I live in an area with better than average seeing conditions on most nights. Even so, with both my 9.25" SCT and 12" reflector, a more realistic formula seems to be 30x per inch of aperture. Newcomers shouldn't be discouraged by this however. On a good night Jupiter will show a stunning amount of detail within the planet's bands at 200x.
