A New Guy Question For My New NexStar 8 SE
Posted 22 February 2013 - 05:32 PM
About 3 weeks ago I made my “first scope” purchase (the $300 Wal Mart doesn’t really count). I decided on a Celestron 8 SE Nexstar. I felt like this was a good beginners scope for observing and well within my budget. The news is even better because my wife has caught the astronomy itch too and is learning with me. The scope so far has performed to all my expectations but I do have one question about it. After a successful alignment (I mean using 3 stars that are far apart and out on the horizon, making my last movement down and to the right, etc.) the scope will slew to whatever I select from any of the menus and place it within the view of my 25mm ep. It seems some nights better than other but it is always there.
However, over time the target object will eventually drift out of view if I don’t manually center it again. I am using the AC adapter so power can't be a problem. Not a big deal really but I guess the engineer in me is always looking to make things better. So I was wondering, from the experiences of veteran users, is this just the limitation of the equipment or if anyone else out here knows if this slight annoyance would be solved by use of an Orion off-axis guider and StarShoot AutoGuider?
That way when I have to step away from the scope for a while to turn over the BBQ chicken that is on the grill and get me another beer when I come back Jupiter is still in my view.
Posted 22 February 2013 - 05:50 PM
A very warm welcome to CN and to this forum in particular. :bow:
I think you'll find that you need to address your anti-backlash settings to effect a cure to this drift.
If you're not sure how it's done, we can take you through the procedure.
Posted 22 February 2013 - 05:52 PM
You've come to the right place to have your questions about all things NexStar answered (although I personally don't have an answer to this question ).
Posted 22 February 2013 - 06:28 PM
Thanks. I just read your post "Re: Nexstar SLT anti backlash settings " is that the procedure you'd like me to try?
Also I'd like to take this time to apologize to all astronomers in the Houston area that have now been socked in by rain and over cast skies for days and days...yes it is obviously my fault.
Posted 22 February 2013 - 06:52 PM
I can't recall that particular SLT thread but this one should help you through all possible "woes" you might initially experience with your new 8SE.
Open the attached link and page down until you get to the 19th entry. You should find a complete instruction sheet I prepared and which our CN colleague, "Hamdul" submitted, for setting up one of these 'scopes.
Hoping this helps but if not, let us know,
Posted 22 February 2013 - 07:09 PM
Posted 22 February 2013 - 07:14 PM
On the first night I was able to observe, I could very easily see the bands of Jupiter. Later, on one great night, I could make out the Great Red Spot in the highest-magnification EP that I have (6 mm). Lots of other great sights to see as well!
You're in for a great ride!
Posted 22 February 2013 - 08:58 PM
I will give those anti-backlash procedures a try. I still am curious though, now that I have posed the question.
Does any one have and good advice for using an Autoguider with the NexStar mount?...I mean it does have a plug for one.
Should I make this question another thread?
Posted 23 February 2013 - 04:24 AM
My advice regarding the auto-guide port on your 8SE is simply to forget it. It's of little or no use: (nor is it designed to be so), in assisting you with 'scope alignment or tracking accuracy. Nor, in fact, is it at all functional when the 'scope is operated in its normal Alt.Az. mode.
In theory, its task is such that coupled to an appropriate guide 'scope, (i.e. your 8SE with attached guide 'scope), it will allow the mount to hold a camera image of a selected celestial object on track, thereby allowing prolonged camera exposure times far beyond those which are possible without a guide system.
In practice however, there is more than a little doubt that the guiding of these, essentially Alt.Az. mounted 'scopes is possible.
In the first place, autoguiding can only take place when the 'scope is equatorially mounted, (in this case, on an equatorial wedge).
Secondly, given that Celestron withdrew their Nexstar series wedge from the market some time ago now, for whatever reason: --- (but having had one myself, let me just say I'm not surprised they did !), --- there is yet another problem; namely that of the Nexstar's spur gear drive.
These spur gear drives are perfectly adequate for visual astronomy and will indeed allow short exposure photography of the Sun, Moon, planets and some of the brighter deep sky objects; even in Alt.Az. mode: but their inherent backlash makes them unsuitable for long exposure imaging, even in equatorial mode; where worm driven gears, with virtuallly no backlash, win out every time.
I hope the above answers your question.
Posted 23 February 2013 - 08:31 AM
Thank you so much Tel.
Posted 23 February 2013 - 10:07 AM
These scopes are quite capable of accurate tracking.. My own 8i (earlier version of the current 8SE) track well enough to keep the ENTIRE FULL moon inside the FOV of the standard 25 mm eyepiece for at least 7 full hours ..most likely about 8 before it hits the edge of the FOV...
BUT it honestly took a lot of tweaking of my backlash settings and a little bit of balancing of the OTA to achieve this kind of accuracy...
I'd start by balancing the scope ...make it just a hair off balance with the bias toward either the front or rear... and make the exact location so you can always mount the OTA in the exact same position...
Now start messing with all 4 of your your backlash settings...and keep messing with them... pay no attention to the numbers because these scopes just set it so the scope stops dead in in tracks without any drift whatsoever when you release a button under slow (rate 2) slewing speeds...and also get a nice smooth start with no jerking at all at the beginning of a slew...Pay absolutely no attention to the delay in the start of a slew the scope may not even start a slew for a second or two after you hit the button... that is normal because those spur gears are sloppy...
Read in the stickies how to balance the OTA on a pencil etc and also how to use a brick wall or a shingled roof to set your backlash settings...
It takes a little time..BUT in the end you can get darn accurate tracking out of these scopes...
Posted 23 February 2013 - 06:00 PM
WELCOME to the Collective! You WILL be assimilated. Resistance is futile.
You are gonna love that 8SE! You'll get that "drift" problem all worked out - especially with the help of the gang here in the asylum.
Just be careful you don't get BBQ sauce all over the eyepieces and don't spill your beer on the scope!