After owning a Celestron C5 750mm for over 20 years, I suddenly found myself living somewhere with a sky worth shooting. The cantilevered foot for a camera tripod that came on the spotter always had in too much vibration on my EQ-2 mount, resulting in barbell stars when shooting deep sky objects. With a little searching, I found a set of 5.5" rings (ostensibly made for a Newtonian) with a Vixen base on eBay. I happened to get an Orion SkyView Pro tripod to carry my new SkyWatcher 180 (with a Vixen base)—overkill for the weight of the newly-ringed C5, but stable as a rock!
With this setup, I finally had a good enough platform to shoot some deep sky objects. The Lagoon Nebula happened to be in an ideal viewing position, so I shot it. The result was fairly impressive:
The edge coma is fairly obvious, which surprises me given that the scope was sold as a telephoto for a 35mm camera (the APS-C crops off an edge that would be more severe). Is there a field flattener that would work on the C5?
Had one for years (the standard astro model, which maybe was slower?). Loved it. A grab and go SCT. Sold it when my eyes were no longer good enough, well before I discovered astrophotography.
The coma is an unavoidable aspect of the inexpensive spherical mirrors used in the SCT. The optical design of the SCT makes for a decent inexpensive long focal length scope, but it is fundamentally flawed, which is why there are no "high end" SCTs. If someone wants to make a high end long focal length scope, they use an optical design with more complex mirrors like a Ritchey-Chretien or a Corrected Dall Kirkham. Physics.
Enjoy it for what it is. Which is pretty nice.
Edited by bobzeq25, 22 July 2017 - 08:23 AM.