Newtonian 8" f/8 Observing Report

Eight Inch f/8 Newtonian
A truss tube telescope you can build at home
First Observing Report

On May 29 I finally had the telescope completed enough for observing. The sky was absolutely clear and I looked forward to putting the instrument through its paces and seeing what I had. The first object I put it on was an inconspicuous star just above a tree to the southwest. Once in the field I was a little disturbed to find the unfocused image somewhat oblong and I instantly wondered if the optics were in some way astigmatic. I adjusted the focus but at 64 X with a 1" eyepiece I still could not see much even when in focus but it definitely was an elongated object. Pushing on, I put in a 1/2" eyepiece I instantly saw it was a double star. I quickly dropped in a 2.5 X Barlow with the 1/2" eyepiece and at 320 X it cleanly and widely divided the pair. I don't know what the star was but I was relieved. The image, however, was not all it could be yet. The night was very young, the air a little unsteady, and the telescope and its optics not fully at thermal equilibrium. I took a peek at Eplison Bootes (Pulcherrima), 2.4 arc sec, and could barely divide it because of turbulence. I let the telescope sit for a while. After about an hour, about 10 PM, I came back out and things were entirely different. Everything had settled down. Pulcherrima was cleanly separated though the atmosphere was not completely stabile. The colors were not as bright as in my 10", scintillation was blowing out the spurious disk and dulling the colors, yet I could easily see the blue in the companion. After another hour I examined Epsilon Lyrae at 508 X. The sky had settled down a bit and each pair was a dot surrounded by undulating fragmented rings. Though the resolving power and colors were a bit lessened compared to my 10" the 8" was noticeably less impacted by the effects of atmospheric turbulence. I then turned the telescope on the notoriously difficult Delta Cygni, 2.5 arc sec with a disproportionally bright primary and faint secondary. At 320, with the air a little turbulent, I could not easily separate the companion, just a hint of a bump on the primary, but at 508 X it fully separated and, with a steadying of the air, became distinct and clear standing away from the primary.

The telescope attained thermal equilibrium in about one hour and there are no fans at the present time. The curved vane spider showed no spikes on Vega. The rotating tube arrangement appears to work very well. The saddle is lined with 1/8" felt and bears against 2" wide Teflon tape wrapped around the central tube.