Refractor vs Reflector
 

 

    Small. Up to 3 inch.

   REFRACTORS. Hardy and robust, easy to use, remain collimated and reasonably inexpensive, especially when made in quantity.

   REFLECTORS.  More complex and go out of collimation more easily than refractors. Mirrors need more maintenance than lenses. Small ones are optically less efficient than refractors, and therefore less common.

 

Medium. 3 inch to 6 inch.

   REFRACTORS. A 3 inch lens is quite expensive - c. £50. As they increase in size the cost rockets to ,say, £500 for a 6 inch. Cannot be made by the ordinary amateur.

Colour correction needed for all telescope lenses means the expense increases with size. More efficient than reflectors at these sizes. They need a long tube, viewed from the bottom, hence a high mount and observatory required.

   REFLECTORS. Mirrors become cheaper than lenses at this size - a 6inch about £50. Mirrors are colour corrected or achromatic. They can be mounted on a low fork and are easier to accommodate.

 

Large. Over 6 inch.

   REFRACTORS. Tend to be far too costly for amateurs. Whereas a 16 inch refractor would cost perhaps £100,000, a 16 inch reflector would be around £1000.

Large lenses can sag when the angle of the telescope is raised. The largest lens, of 49 inches, was shown at the Paris exhibition of 1900, but never used seriously. The largest in use today is the [‘Yerbs’ / ‘Terbs’ (cant read writing)] 40 inch lens.

   REFLECTORS. Those of more than 6 inch are the only practical answer for the amateur because the cost rises only moderately with increasing size, .Also, mirrors can be supported across the entire back, cutting distortion, while lenses have to be supported at their edges. Fairly large mirrors can be home made. The largest mirror is the Russian one of 236 inches, although multi-mirror systems of greater area are being planned.