The Telescope and Related Hardware

 

Here is the scope, with me taking the picture standing on a ladder looking through the slit of the dome. That's the only way I could get almost all the scope in the shot:

newscope.jpg

The scope has a 16" f/4.9 Newtonian primary, figured by John Hall of Pegasus Optics. The figuring results show with 95% confidence, the Strehl ratio is greater than or equal to 0.95. John rates the mirror as "excellent." My experience bears this out. My previous mirror, while a fine mirror, had a bit of a turned down edge along a part of the circumference. I can see the difference, both visually and for imaging. Also, it really helps the collimation process if you know the primary is not the fault for some intermediate, not-quite-right collimation step. I've coupled this fine 16" primary with an excellent 3" Keller/Wynne coma corrector. After the best collimation I've ever had with a 16", I now consistently get nice round stars. The final say on collimation is always what your images show, and by using the 3" coma corrector, I could finally know when a good collimation was obtained. The small adjustment steps were made easier, especially after I installed one of Paul Van Slyke's rock-solid spider vane and diagonal holder assemblies. See spider.jpg. Here is a picture of the 3" coma corrector attached to an ST-10XME: coma/st10.jpg. When I shoot color images, I simply replace the ST-10XME with a ST-2000XCM. Here is a picture of the unit slid into the drawtube of the Van Slyke 3" focuser: focuser.jpg. The focuser is driven by a Robo-Focus. The tube for the OTA is a 19" OD solid fiberglass tube from Parks Optical. The 16" mirror is mounted in a 16" Parks mirror cell, which has three pushing lock down bolts, which helps a lot in holding the floating cell in place with different tube orientations.

Here is the mount, an MI-500 GEM from Mathis Instruments:

mount_pier.jpg

I am an old ATM nut, and I love the "Porter-cone" surrounding the RA axis. It gives an air of classic grace and fundamental stability. The mount sits on a wooden pier I built out of nine pressure treated 6 ft long 4 x 4s, bolted together in a square pattern. It is sunk in about 1.5 cubic yards of concrete. The concrete slab upon which the dome sits, is isolated from the big cube of concrete in the ground supporting the pier, with about 8" of dirt separating the two.

The MI-500 is fully computer controlled, and is a joy to use. It has a small raw +/-3.5" periodic error, and tracks beautifully. I use The Sky to control the pointing of the scope, interfacing to the AP1200 computer control of the MI-500 using a PC installed in the dome. I ran an ethernet cable to the dome and installed a 1 Gbps network to control the 1 GHz PC dome computer using PCAnywhere running on a 3.4 GHz PC inside my house. The rotation of the 10 ft Pro-Dome's hemisphere is motorized and controlled using Robo-Dome, and communicates to The Sky to automatically keep the dome slot over the scope. As you can see from the wide field view on my opening page (see side_view.jpg), the dome is not very far from the house, and that's good, because even though I've attained near complete automation, I still go out there when needed during a night of imaging.

The computer in my dome stands in the NW direction inside the dome, towards Denver. I built a small work shelf, under which the computer sits. See computer.jpg. Even though the computer uses a full tower case, there is still plenty of room to walk by it and the scope. I installed two extra wall rings in my 10 ft Pro-Dome (5 ft total), and its amazing how much more head room that gave to walk around. Another benefit of the two extra wall rings was that now, I could modify the door so that it can be opened and closed even when the slot is pointed in any direction. There is a substantial sky glow along the horizon in the Denver direction, and I never image towards the NW. My NE skies are still pretty dark, and I can catch anything "around the pole" there. The skies to my east are best, where I usually start imaging an object when it attains at least a 45 deg elevation. Imaging usually proceeds through meridian passage, where then I do a meridian flip, rotate the coma corrector/camera unit 180 degs, and continue imaging as the object continues to move towards the west.


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