• Laser collimator, dot only (like a Howie Glatter)
• Headset magnifier (like an OptiVisor)
• Inspection mirror (angled mirror on a stick)
• Small diffuse or side-illuminating flashlight
• 2.5, 3, and 4 mm hex keys for the scope, also whatever you need for focuser tilt
• #2 Phillips screwdriver (to set focal length if necessary)
1. Set focal length (if necessary). This scope is widely spec'd as 1625 mm focal length, but it is actually 1600 mm. See post here: https://www.cloudyni...rs-for-gso-rc-8 . The OPT website and some others have it correctly now. When you set the focal length to 1600 you also get the spec'd back focus of 250 mm.
It is important to have the correct focal length for an RC scope. This generally needs to be done under the stars with a plate solver. If you decrease the mirror to mirror distance by x, you increase the focal length by at least 10x. Note that increasing the focal length will increase the back-focus, too, and vice-versa.
Adjust focal length by moving the secondary incrementally in or out using the center screw while keeping the three tilt adjustment screws snug. To move the secondary, the center screw is pull: CW pulls the secondary mirror away from the primary and reduces the focal length. The three hex screws are push: CW on them pushes the secondary mirror toward the primary and increases the focal length. Loosen the push before pulling and vice-versa.
2. Reset the primary (if necessary), maintaining focal length. Do this if you know your primary is way out of whack. Fully loosen all the small black primary screws, tighten the large silver screws all the way (counting 1/6 turns by flats on the hex keys), then loosen them the same number of turns each (the average of the tightening turn counts) and tighten the black screws. This maintains the focal length you set in the previous step.
3. Reset the focuser tilt (if necessary). For a Moonlite CS: loosen the focuser rotation lock thumbscrew and all four focus tilt setscrews. The focuser is now loose on its flange. Pulling the focuser away from the OTA, tighten the tilt adjust setscrews until they all just make contact with the same snugness. Focuser rotation will drag slightly at this point.
4. Adjust focuser tilt so the laser dot points directly at the secondary donut. Insert the laser snugly into the focuser. You can clearly see the secondary donut by looking in from the OTA open end and using the headset magnifier, inspection mirror, and a diffuse or side-illuminating flashlight hung on a hook inside the OTA a few cm. The magnifier lets you see the donut in good detail from close up. The flashlight illuminates the secondary donut from inside the OTA so you can see it more easily, and it eliminates the visual dazzle of the laser dot. The inspection mirror is an angled mirror on a stick so you can look back at the secondary mirror from the open tube end.
5. Adjust secondary tilt until the reflected laser dot is centered on the laser source. Use binoculars from the OTA open end to see a reflection of the laser source face in good detail. Yes, good old field glasses! I was amazed that this worked, but the effective distance to the laser source image is far enough that you can use binoculars. This brings the laser source image up close and you can make a good judgment on how well centered the reflected dot is. The reflected "dot" is actually smeared out by the secondary with many diffraction rings visible, but you can center it well by eye this way.
6. Adjust the primary tilt using a Cheshire. Install the Cheshire snugly in the focuser. Look through the Cheshire "pinhole" and center the dot (the reflection of the pinhole) in the secondary mirror donut. This is hard to explain but easy to do with precision once you see it.
7. Iterate steps 4 – 6 until converged.
8. Fine tune the primary tilt with a star near zenith (if necessary). I used this primary fine-tuning method from Vixen. Place an out-of-focus bright star in the center of the view. Move the scope so the star donut moves in the direction of the narrowest part of the donut. Adjust the primary in the direction to bring the star back toward center. This eliminates guesswork over which primary screw to adjust. My scope only required about 1/16 turn on one primary screw.
Edited by TinySpeck, 05 August 2020 - 03:39 PM.