For other images, click here. |
The 18 inch scope and suburban GRB imaging. Go Here |
13.5 or better, and these were good zenith skies for Rockville, but otherwise unexceptional. I want to contrast the 13.5 mag LM indicated here with the magnitudes observed using the C8 under the Teledome. Consider this. To achieve that level of seeing, I sat under the dome for over 20 minutes to dark adapt. Using the NGT-18, I simply put a towel over my head to mask out the ambient light from my house, the street light, my neighbors porch lights, and the general sky. In comparison, I saw an increase in at least 1.5 magnitudes over the C8 under similar conditions. Having 5 times the light gathering capacity of the C8, I would expect about 2 magnitudes of improvement. I got 1.5, but without being dark adapted like I was in the tent. The scope has one feature that is worth it's weight in gold. The rotating nose. Because of the German Equitorial mounting, as the telescope is moved from location to location in thesky, the position of the eyepiece changes from comfortable positions, to absolutely terrible locations. JMI solved this problem by constructing the nose assembly such that it can be rotated to provide the best viewing angle. This benefit has a small number of drawbacks. 1) Columnation is better at some locations than others. 2) The Telrad finder if set at one position, is off by as much as a degree when moved to a second position, although this problem can be mitigated by the use of a shim. Another wonderful aspect to this scope is it's Galaxy mirror. The mirror weighs about 50 lbs, and it is mounted in such a way that it can be removed from the scope in about 5 minutes. The mirror provides superior views using the 20, and 35 mm Nagler eyepieces, but also provides wonderful views through the 13 mm and 9.8 mm naglers, and even the 4.8mm eyepiece. Polar alignment is performed using the azamuth bar. |
NGT-18 |
The NGT-18 is an 18 inch f/4.5 split ring equitorial newtonian telescope. The mount for this scope is extremely stable. The split ring provides a very large guiding and tracking "gear". The gear is about 36 inches in diameter. It provides the same function as much smaller (6-7 inch) drive gears in C8's. |
The scope weighs over 200 lbs, and so comes with handle bars and wheels. With these attached, it works like a wheelbarrow. I use a wench for moving it up a ramp into the back of my mini-van for transport to dark sites. I live in the Washington DC suburbs outside the Beltway (about 16 miles from city center). The skies here are not very good. One of my solutions to this problem was to add aperture. The result of this activity was the purchase of this scope. |
March 30, 2000, I used the scope to observe M67 shown at right. The image was taken using a C8 and ST-6 camera using a 15 second exposure on an evening of similar seeing to last evening. I could see visually using the NGT-18 most of the stars shown in this image. The view was less contrasty, and I couldn't see the faint stars on the image, but I was seeing to magnitude |
13.5 or better, and these were good zenith skies for Rockville, but otherwise unexceptional. I want to contrast the 13.5 mag LM indicated here with the magnitudes observed using the C8 under the Teledome. Consider this. To achieve that level of seeing, I sat under the dome for over 20 minutes to dark adapt. Using the NGT-18, I simply put a towel over my head to mask out the ambient light from my house, the street light, my neighbors porch lights, and the general sky. In comparison, I saw an increase in at least 1.5 magnitudes over the C8 under similar conditions. Having 5 times the light gathering capacity of the C8, I would expect about 2 magnitudes of improvement. I got 1.5, but without being dark adapted like I was in the tent. The scope has one feature that is worth it's weight in gold. The rotating nose. Because of the German Equitorial mounting, as the telescope is moved from location to location in thesky, the position of the eyepiece changes from comfortable positions, to absolutely terrible locations. JMI solved this problem by constructing the nose assembly such that it can be rotated to provide the best viewing angle. This benefit has a small number of drawbacks. 1) Columnation is better at some locations than others. 2) The Telrad finder if set at one position, is off by as much as a degree when moved to a second position, although this problem can be mitigated by the use of a shim. Another wonderful aspect to this scope is it's Galaxy mirror. The mirror weighs about 50 lbs, and it is mounted in such a way that it can be removed from the scope in about 5 minutes. The mirror provides superior views using the 20, and 35 mm Nagler eyepieces, but also provides wonderful views through the 13 mm and 9.8 mm naglers, and even the 4.8mm eyepiece. Polar alignment is performed using the azamuth bar. |
JMI |
The 18 inch scope and suburban GRB imaging. Go Here |
For other images, click here. |
