SIX INCH F/15 REFRACTOR

The 6" f/15 refractor was constructed approximately 1993. The construction of this telescope in terms of materials and technique is very similar to my 10" f/8 reflector. Once again, the tube breaks into two pieces and is constructed of Sonotube and plywood. The flanges that hold the two tubes together are made of plywood. The most unique aspect of this refractor is that in order to make the instrument at least somewhat portable the mount had to be so designed to be closer to the ground. Conventional refractors have their mounts high in the air so that the lower end of the tube can swing through a complete zenith arc and still give the observer room to look up through the end of the instrument. Inasmuch as most refractor users employ a star diagonal most of the time anyhow I simply decided to incorporate a permanent diagonal into the design and counter weight the rear end of the tube, thereby resulting in a much smaller movement of the eyepiece. This allows me to keep the mount much lower to the ground. The tube is extended somewhat beyond the diagonal and eyepiece so as to form a counter balancing lever. A flange and stub pipe nipple extend out from the end the tube from which are mounted counter balance barbell weights. For most observing situations the eyepiece is in an extremely comfortable position and observing can usually be done seated on a stool. The scope is particularly good for children at star parties inasmuch as they do not have to climb a ladder.

The instrument was largely the result of a desire to begin experimenting with different kinds of achromatic and apochromatic objectives. I simply needed a vehicle in which to test objectives corrected in various ways. To that end the telescope has held conventional air-spaced doublets, oiled doublets, and even a glass liquid (GLAPO) apochromatic objective. Just for fun, a second tube top was made to hold a 4.5" f/18 air-spaced (currently oiled) apochromatic objective. Under certain conditions this telescope is capable of producing absolutely startling images of the moon. Because of its small aperture and extremely high resolving power it makes the most out of whatever seeing conditions are available here in New England. I have made many doublet objectives and am constantly experimenting with different designs. The six inch refractor is a unique and exciting instrument that has held an important place in astronomy for over 150 years.

You will notice that the same equatorial mount is used for both the 10" reflector as well as in this 6" refractor. The only difference is the 4" supporting column. With the reflector I use a two foot long pipe and with the refractor a four foot long pipe. This way I get double duty from a single mount.

Comfortably seated and observing the solar eclipse of May, 1994.

Note the flange approximately in the middle of the tube. Six 1/4-20 carriage bolts with wing nuts hold the two halves of the tube together. Also note the hole at the top of the tube. This hole, along with leaving the access door open at the bottom of the tube (as is seen here) results in rapid equilibrium of the objective.

Saddle and finder scope. The finder scope is a old Mead 60 mm job I picked up at a swap table. The finder rings are made from the flange ends of a 3" PVC tee. Mounts holding the rings to the tube are made from plywood treated and painted. The subtle flexibility of the plastic rings make them excellent for adjustment purposes.

Bottom end of tube showing counter balancing rubber covered barbell weights.