Newtonians since the longer focal lengths yield higher magnification and require smaller secondary mirrors, thus less obstruction of light for the primary. I am partial to f/6 to f/8 Image 3 – M33, the Pinwheel Galaxy, captured in a 35-minute exposure with a Discovery 8-inch f/7 Newtonian. And Newtonians with high quality optics provide exceptional views and images. Newtonians are by far much less expensive per inch of aperture to manufacture than any other telescope design. At f/7, there is no hint of coma in the images and stars all round out to the edges of the images. Both images demonstrate that high quality images can be obtained with a fairly inexpensive 8-inch Newtonian telescope. Image 3 is the same configuration with a 25-minute exposure of the Pinwheel Galaxy (M33). Image 2 is a 55 minute prime focus exposure of the Horsehead Nebula (IC434) taken with the 8-inch 1422mm focal length Discovery telescope. The focuser handled the weight of either without flexing. Most of my images with this scope were taken with a Canon 30D DSLR camera or a SBIG ST-2000XCM CCD camera. ![]() Still I had little difficulty achieving focus for CCD or DSLR imaging. Back then the standard focuser was single-speed 1.25-inch rack and pinion focuser. The only thing that could have been improved was the focuser. The four-vane spider, secondary mirror assembly and primary mirror cell were much higher quality than those components in imported 8-inch Newtonians. This material has very low thermal expansion and less flexure than Newtonians made with thin sheet metal tubes. The optics were contained inside a Sonotube-like tube with a flat back interior finish and a nice glossy black exterior. Although configured as a Dobsonian, I removed the optical tube assembly (OTA) and mounted the scope on a Parallax HD150 German Equatorial mount using a set of Parallax tube rings. ![]() Then in 2005, I purchased a Discovery 8-inch f/7 Premium DHQ Newtonian to use as the main imaging instrument in my backyard observatory ( Image 1). ![]() Image 1 – The author previously used this Discovery 8-inch f/7 optical tube assemble in a roll-off roof observatory. The larger focal ratio provided virtually coma free viewing. A few year later, I purchased a Discovery 8-inch f/6 Newtonian for my son for his 21 st birthday. The telescope is still in use on my brother’s ranch in the Texas Hill Country. He has played a major role in several observatory projects including the Powell Observatory project, which houses a 30″ (0.75 m) Newtonian, rebuilding and installing an 8″ (0.20 m) Alvin Clark refractor in a new observatory built for it at the Naval Academy and was the initial director of the Coast Guard Academy Astronomical Observatory in Stonington, CT, which houses a 20″ (0.51 m) Ritchey-Cretien Cassegrain telescope.įifteen years ago, I bought my first Discovery telescope, an 8-inch f/5 Newtonian. from The Johns Hopkins University, both in planetary science and is an associate provost at Gardner-Webb University in Boiling Spring, N.C., and a professor of physics and astronomy. in physics from the University of Central Florida and a M.A.
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