Modifying an XT6 for better planetary observation?
Posted 05 December 2012 - 10:22 AM
I've really been enjoying the fantastic views through my recently acquired Orion XT10i, a purchase I anguished over for, oh, 15 or so years! I couldn't be happier. I bought the scope with the intent of focusing my viewing on dim DSOs, but am finding that looking at the planets is equally (if not more) fascinating, and in my light polluted back yard, a much more practical pursuit.
I've read a bit about scopes for plaentary observation, and was wondering why I haven't read about people modifiying the XT6 for such a purpose. Seems it'd be a quick and easy mod. The scope already has an appropriate focal length (f/8) and if one were to swap out the spider and 34mm secondary for a 1-inch secondary like this one, along with an appropriate spider, the secondary mirror obstruction would drop from 23% to 17%.
Would this be a better scope for planetary observation than my current XT10? Even if it were just "on par" with the XT-10, I'd consider getting one and modding it just so I'd have the smaller scope to haul out for looking at planets. Maybe even put it on a GEM so it would be easier to share the view with friends (and not have to slew the scope every 30 seconds).
Someday I'll probably grind my own mirror and build a scope from the ground up, but in the meantime, this seems like an inexpensive way to get better views of objects in the solar system. Thoughts?
Posted 05 December 2012 - 10:34 AM
Posted 05 December 2012 - 10:36 AM
Would this be a better scope for planetary observation than my current XT10? Even if it were just "on par" with the XT-10, I'd consider getting one and modding it just so I'd have the smaller scope to haul out for looking at planets.
First.. Hello and Welcome to Cloudy Nights..
As the owner of a venerable RV-6 (6 inch F/8) and a basic 10 inch F/5 Dob, in my experience a decent 10 inch F/5 Newtonian that has cooled and is properly collimated will easily out perform a 6 inch F/8 when viewing Jupiter, Saturn, Mars and the moon. Both scope provide decent planetary views but the larger aperture provides increased resolution and increases the contrast of the fine planetary details, the difference is quite apparent to my eye.
Posted 05 December 2012 - 11:22 AM
It's that "all things being equal" thing, and often they aren't. There's a lot of variables - and gremlins! - that can affect viewing and even how we view (eq vs. Dob, etc.). It's why many amateurs wind up owning more than one telescope - they serve different functions at different times.
Posted 05 December 2012 - 11:50 AM
That's kind of what I expected. I can't remember why longer focal lengths are better for planetary viewing , but I guess I thought that the secondary mirror obstruction percentage impacted contrast the same regardless of primary mirror size. Sounds like the truth is that aperture trumps the benefits of a lower percentage of secondary mirror obstruction?
Orion sells a 6-inch newt on an equatorial mount. I was thinking I could use that mount with the OTA they sell with the XT6 for a light and transportable scope for looking at planets. Maybe that OTA is too long/heavy for that mount anyway...I haven't done enough homework.
Posted 05 December 2012 - 12:44 PM
...I can't remember why longer focal lengths are better for planetary viewing :confused
Longer focal lengths are often preferred because they have less coma (sideways blur) near the edges of the field of view, which can be important on a non-motorized mount where you'll allow the target to drift across much of the field of view before re-centering. Long focal lengths also yield higher magnifications with longer focal length ep's, which are, in general, easier to observe with than little 'pinhole' eyepieces.
Biggest issue is thermal management. I'd address that in both scopes before doing anything with the secondary in your 6". Add fans to both, and consider adding Protostar's tube inserts, which will dramatically reduce tube currents that are the result of the top of the tube cooling below ambient by radiant loss of heat to the sky (and space). This done, you'll choose between the 6 and 10" by how much time you have for allowing the primary to cool.
Posted 05 December 2012 - 06:03 PM
Posted 05 December 2012 - 06:18 PM