A Cheap
Refractor or a Cheap Reflector
by Geary Keilman
Today, there are a number of scopes, both refractors and reflectors, with acceptable optics that are available for less than $200. While this market is aimed at beginners, experienced observers may also want a small, inexpensive “grab and go” scope. The question is; which performs better, the cheap reflector or the cheap refractor. To find out, I took out an Orion 80mm Short Tube refractor and a Orion 4 1/2” StarBlast reflector to do some side by side testing. Both scopes are marketed by Orion and are made in China. The refractor appears similar to those marketed by other firms and was mounted on an Orion equatorial mount that was purchased separately. The StarBlast was mounted on the modified Dobsonian mount that came with the scope. They both have similar focal lengths. The same eyepieces were used in both scopes. The seeing was good and the transparency excellent on the night of the test.
The first target was Polaris to see if I could find its elusive companion. I also did a star test on both scopes using Polaris. The little refractor appeared to be well collimated with no sign of astigmatism. However, when I racked it both inside and outside of focus, the diffraction rings indicated a fair amount of spherical aberration. I looked for Polaris’s companion but it was a no show. The StarBlast was also well collimated and the star test revealed a well figured mirror with very little spherical aberration. Polaris’s companion popped into view at about 70 power and was separated nicely at 130 power. Polaris was also brighter in the StarBlast due to its greater aperture which may also account for the greater ease at splitting Polaris.
I next turned to Saturn, which was in very good position for viewing. The image in the refractor was fairly soft, especially at high power. The Cassini division was not discernable. To its credit, there was very little violet or blue fringing usually associated with fast, inexpensive achromat refractors. A Bader contrast filter was used to try and sharpen the image but did little except dim the view and change the color slightly. The StarBlast faired much better. Again, the image was brighter. Saturn revealed its Cassini division as well the equatorial band.
Wide field views in both scopes covered a lot of sky owing to their low focal ratios (focal length divided by aperture diameter). Both also showed a fair amount of coma (curved star images) near the edges. I would rate this one a draw.
While, the Moon wasn’t up that night, I have observed it at different times through both scopes. Both did well but the refractor did have noticeable blue fringing. Once again, the contrast filter showed little or no additional detail but dimmed the image and made the Moon slightly yellow. The StarBlast showed better contrast with inky black sky against the brightness of the Moon.
In summary, the reflector outperformed the refractor in nearly every instance due to greater aperture, resolution and optics. It was also less expensive. On the down side, it must be collimated (aligning the mirrors) regularly and has an open end which lets in dust. The refractor is nearly maintenance free can be used for astrophotography and may be used for terrestrial viewing with the supplied 45 degree diagonal. If you don’t include the mount, the Short Tube is smaller than the StarBlast. One other comment: the mirror quality in inexpensive reflectors tend to vary somewhat. The one I tested is probably one of the better ones. If you are having a tough time deciding which one to get, buy one of each, they’re cheap!