Just a general question: I have a newly acquired Paramount ME, and T-Point. I have adjusted the pier on multiple occasions, and I have measured the tracking error. When I leave the clock drive on and come back in one hour, the stars have moved 30 seconds of arc. I don't have a good idea of whether or not that is very good, just good or whatever? Please let me know how good does it have to be. What do other people have for their tracking errors? Thanks, Bob.

Bob,

Your tracking will be as good as your polar alignment.

My mount is polar aligned (measured with T-Point) to less than 30 arc-seconds of the pole in Alt and Az.

I believe Mr. Smith has some information on how well he was ale to tune his ME for unguided imaging.

He can provide a much better answer to this questions.

rb

Thanks Richard: I have a follow up question. I have the results of the T - Point, and lately they have been around l.2 minutes and 1.4 minutes off. So, I guess I need to further adjust my mount. Anyway, my question is: How much better is it to map 150 stars than 75 stars? Is it a big difference? Also, when you use Automapper (I have not yet), does it take CCD photos and then compares them to THE SKY. I wasn't really sure? Thanks, Bob Caton

Bob,

Let me jump in a bit here. With a properly set up ME, I would expect unguided star tracking of +/- 10 arc-sec. peak-to-peak over a 4 hour period! I achieved these results a couple of years ago. So, what is needed to achieve this?

1. As Rick said, an excellent polar alignment to the refracted pole. This is most accurately determined with a series of 50 - 100 point Tpoint models. After rough alignment, use progressively more points and fit the model. If you have a fixed observatory, then a series of 100-point runs, easy enough with AutoMapper, can get the polar alignment really dialed in. You should be within 30 arc-sec. of the refracted pole.

2. A deep and well-fitted Tpoint mode. I use a 300 point model but I am a bit compulsive For this I use AutoMapper. Automapper takes images at various locations arountd the sky, calculates the equatorial coordinates of the center of the image by plate solving and compares that solution to the telescope's indicated equatorial coordinates, and passes the info to Tpoint?TheSky to develop the raw data for pointing correction. From this point the Tpoint model can be developed. With a good fit, you should expect to se an RMS pointing error of 20 arc-sec. or less (300 points, 12 terms).

3. An accurate Periodic Error Correction. For this, I recommend PEMPro as easy to use and giving excellent results. Your resultant periodic error after correction should be below 0.6 arc-sec. peak-to-peak.

4. And, it goes without saying, a stable or at least repeatable optical path. That doesn't mean it can't change as long as it changes repeatably.

All of this requires some care and attention to detail but is quite doable and many ME owners achieve these kind of results.

John
CCDAutoPilot author

Thanks John: I have a fixed observatory with a 16 inch Meade LX 200 on the Paramount ME mount. So, I guess I can strive for the 10 second error over 4 hours. What do you know of Andy Homeyer's scope cradle, and how much better is that to have? Will it prevent some flexure, and if so, to what degree. Thanks, Bob Caton.

Bob,

While I have no direct experience with Andy's cradle, I have heard nothing but good about it. As to flexure, I don't think the cradle will be the issue. I think the larger issue may be stabilizing the pirmary mirror. I assume you will be using some kind of mirror lock and secondary focuser. Again, to the extent the optical path is stable or at least repeatable, you should do reasonably well. The numbers I mentioned in my earlier post were achieved with my ME and a 14RC truss by RCOS.

Dear John: Thanks. I will be able to lock the primary mirror. Also, I recently bought A bunch of Van Slyke components. I just bought the Van Slyke rotating cycloid (so you can rotate an image initially to match the CCD field), then, the Van Slyke McCray focuser with Robo Focus, and then a off-axis guider with three extra ports, and then a SBIG 10 XME CCD camera at the end of the imaging train. The Van Slyke components are very rigid, and I don't think flexure will be any problem. I just need more counterweights for the Paramount, so I bought another 50 lb. weight on top of four 20 pounds ones. Do you have any experience with the Van Slyke components? They are a bit expensive, but from I have read, they work superbly. Let me know your thoughts on this. Thanks, Bob Caton.

Bob,

No, I don't have any direct experience but I had a client that had to blacken certain parts of his VanSlyke to prevent poor flat fielding due to internal reflections. Others may have different experience. My OAG was made by Andy Homeyer, which is excellent. Details here:
http://www.hiddenloft.com/notes/ip.htm

Bob, I am in the process of moving my Meade 16" to a Paramount. Any suggestions from your experience? Any issues with stripping it down to the OTA? BTW, I am going to use Andy's cradle.

Bob Frerichs

I was looking for other amateur astronomers in Mammoth. Contact me at larrys3255@gmail.com and perhaps we could chat about our hobby.

Larry Simpson