Monday, April 15, 2013

The Celestron FirstScope, A Review

My propensity for buying small telescopes tends to be a gamble. Many times, they are just not that good. Other times, there are components that show so much promise yet fall short due to small details (some of these are salvageable). Every once in a while, you find a real gem.
So it is with the Celestron FirstScope. This is a very small Newtonian telescope, 76mm in aperture with a focal length of 300mm focal length. That last number, the focal length, is important, yet somehow Celestron neglected to include it, at least not directly. More on how we determine that in a bit.
So, what comes in the box?

The telescope is very well made for the price. The focuser is set for standard 1 1/4" eyepieces. Around the outside of the optical tube assembly are the names of astronomers, plus the occasional "Galileo 400"; like the GalileoScope, this telescope was made for the International Year of Astronomy 2009, the four hundredth anniversary of Galileo's first telescopic observations. While most of the components are made of plastic, they are very well engineered. 

The telescope is mounted on a sidearm Dobsonian mount. There is no tripod, this is a tabletop design, but one that is very well made. The base moves easily and can be easily tightened if necessary. The altitude axis features a large knob for tightening. 

The instructions are really pretty basic, but then again this is a pretty basic telescope.

There is also a flyer advertising an accessory pack, including a finder scope, something which is not included in the kit. The separate accessory kit also contains two more eyepieces and some astronomy software as well as a carrying bag. This separate kit would be useful for the finder scope and carrier, but we will discuss the eyepieces in a moment.

Now, back to the optics. Included are two eyepieces, an H 20mm (Huygens) and an SR 4mm (Symmetrical Ramsden). 

They yield 15 and 75 power respectively. This information is included on the box, and provided us the necessary information to determine the focal length (for the uninitiated, magnification is obtained by dividing the focal length of the objective, the primary lens or mirror, by the focal length of the eyepiece). By working backwards, multiplying the focal length of the eyepieces by their power, the result was 300mm, our focal length. 
Our main mirror is not parabolic, like you'd find on most Newtonian telescopes, but spherical. A spherical mirror is easier to make, therefore making the price lower (the FirstScope can be had for between $25 to $49.99). The problem is that spherical mirrors have a reputation for being somewhat hard to work with on short, fast focal lengths, and our little FirstScope has a focal ratio of 3.95, making it quite short and fast. Unlike parabolic mirrors, spherical mirrors do not focus colors to a single point. Normally spherical mirrors work well for longer tubes, but our little mirror seems to work fine, but with caveats.
The included eyepieces are adequate, but could (or should) be replaced. The 20mm works the best, but has distortion as you head out towards the edge. It's field is also not terribly wide. The eye relief, how easy it is to view using the eyepiece, is decent, but not great. The 4mm is worse all the way around. It is serviceable, but not great.
It is that smaller eyepiece that pushes this instrument to the limit of its capabilities. The eyepieces included in the accessory kit are a 12.5mm and a 6mm. 6mm would yield 50 power, probably the most comfortable maximum this scope can achieve. However, this telescope works better with lower power eyepieces, ones with longer focal lengths.
I decided to test the FirstScope out on the thin crescent Moon this evening. The included 20mm eyepiece worked fine with the aforementioned considerations. But the view was good enough. Through the 4mm eyepiece, going to 75 power, the field of view was narrower but still yielded a recognizable Moon. Be aware, though, that the eye relief on this eyepiece is not very good.
As I said, the included eyepieces are probably best replaced, though the 20mm is better and should suffice. I switched to an older 20mm Kellner eyepiece, a sort of eyepiece that can be obtained cheaply. The view, while still 15 power, was vastly improved. The field of view was flat edge to edge with no distortion or discoloration.  From there I tried a variety of eyepieces, even some of my better .965" eyepieces, and the views were great.
Additional targets were chosen. The Pleiades looked good even with the included 20mm, but really improved with the 20mm Kellner. The sword of Orion, as well as the nebula, really incandesced, even under suburban skies. My last target was the optical binary Alcor and Mizar and searching for Sidus Luduviciana, their even fainter "companion". Again, satisfactory to great depending upon the eyepiece.
Bottom line - I recommend this telescope, but also recommend replacing or supplementing the eyepieces (you can probably keep the 20mm, as I've previously mentioned). It is great for looking at the Moon, but really excels at sky sweeping, taking in wide sections of the night sky and looking at groups of stars. In fact, if that is the route you choose for this instrument, you can probably do away with the notion of a finder scope entirely and simply use a lower power eyepiece to "sweep" in on an object and then switch to a higher power eyepiece as needed.
Otherwise, it is definitely worth the money, and should make a great "first scope".

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