Jump to content


Photo

Point To, or Manual Setting Circles?

  • Please log in to reply
5 replies to this topic

#1 Brent Campbell

Brent Campbell

    Messenger

  • -----
  • Posts: 443
  • Joined: 09 Feb 2010
  • Loc: Olympia, WA

Posted 29 May 2013 - 08:31 AM

I'm looking at adding GOTO capability to one of my two scopes. For reference I already have a tablet computer. For now I don't want to defork my SCT. I am considering these options:

1) Purchase an inexpensive GOTO scope, add a laser pointer, and make a "point to" scope setup. I was considering the IOPTRON Astroboy or the Celestron Nexstar 60 GT. Cost around $125.00

2) Use the Setting circles on my mounts. Do a rough polar alignment, then point to a known star. Use Sky Safari to find the RA and DEC settings and adjust my setting circles accordingly. Then use the setting circles to find other objects. Cost $0.00 This option seems complicated but I think it could work.

3) Replace my CG-4 setup with something different. Such as the Celestron 102GT. This is a variation of option #1. Turn my wide field instrument into the point to. This would kind of hurt. I just recently got my Orion Express 80/CG4 setup and its starting out good, and getting better every time I use it! Cost $0 if I sell the Express 80, $200.00 used.


Complicating my decision is that I am wary of used Nexstar mounts. I was burned once before on purchasing a used Nexstar mount but I did end up selling/trading/ or using more value in the parts from that mount than I had into it. I just don't want to put allot of cash into a goto mount where I don't have a warranty.

Has anyone tried some of these options? Opinions? I'm trying to rule out the bad options before spending time (limited observing time) or money (usually more limited).

#2 Geo.

Geo.

    Mercury-Atlas

  • *****
  • Posts: 2790
  • Joined: 01 Oct 2008
  • Loc: Upstate NY

Posted 29 May 2013 - 08:52 AM

Why not digital setting circles? Need to mount encoders on your Ultima. ATM102s go about $50 the pair at DigiKey. I have the special bolt you'll need for RA in my junk box. The Dave Ek interface kit goes for under $50 and it should talk to Sky Safari. Add a RS232 to USB adapter and you should be there. Or Bluetooth and no wires. I can hold your hand. Got'ta be easier than the LX50......

Attached Files



#3 Brent Campbell

Brent Campbell

    Messenger

  • -----
  • Posts: 443
  • Joined: 09 Feb 2010
  • Loc: Olympia, WA

Posted 29 May 2013 - 09:31 AM

I thought about that but the encoder hardware mounting cost more than the cheap goto scopes....If I went that way I would purchase a encoder and mounting kit for the Ultima mount. JMI or Lumicon may still have these. This would greatly simplify my installation and avoid hacking the mount. These "retro fit" kits are getting harder and harder to find however.

#4 Kendahl

Kendahl

    Vostok 1

  • -----
  • Posts: 118
  • Joined: 02 Feb 2013

Posted 29 May 2013 - 11:03 AM

We have an Orion SkyView Pro mount with setting circles and a polar alignment scope. The diameter of the setting circles is 3.4 inches. Minimum graduation on the RA circle is 10 minutes. (4 minutes = 1 degree.) Minimum on the dec circle is 2 degrees. I figure I can set the RA to 2 or 3 minutes and the dec to 1/2 a degree.

If you cannot use a polar alignment scope to get a good polar alignment, I don't think setting circles will work for you.

First step when we set up is to get the best polar alignment we can using the polar alignment scope. Before looking for an object, we point the telescope at a nearby star and set the circles to its coordinates. Then, we release the axis locks and move the mount to the coordinates of the target. The largest field of view we can get through the eyepiece is 1.4 degrees. Most of the time, the object lies within the field. The rest of the time it is just outside.

We try to pick a reference star as close as possible to the target. For example, to find M81 and M82, the reference would be Dubhe. For M15, it would be Enif. For M57 (Ring Nebula), it would be Vega. You won't be able to set up on one reference star and find everything else from it. (GoTo systems have the same problem and allow you to use a nearby reference star to tweak accuracy.)

What you will have to do with your mount is decide how accurately you can set it. What's the biggest field of view you can get? If the possible error in setting is larger than the field of view, this isn't going to work. The object will be nearby but you will spend significant time searching for it.

#5 jgraham

jgraham

    Voyager 1

  • *****
  • Posts: 13686
  • Joined: 02 Dec 2004
  • Loc: Miami Valley Astronomical Society

Posted 29 May 2013 - 07:10 PM

I was considering using the setting circles on my newly restored LX6, but I am soooo spoiled with my point-to system. The only problem that I have with it is that I want a better handset to have easy access toba larger database.

#6 Geo.

Geo.

    Mercury-Atlas

  • *****
  • Posts: 2790
  • Joined: 01 Oct 2008
  • Loc: Upstate NY

Posted 02 June 2013 - 10:26 AM

I thought about that but the encoder hardware mounting cost more than the cheap goto scopes....


Yes, the prices are fairly obscene. I have a junk box with enough stuff to do an Ultima and PowerStar I'm going to break up for part that has encoders mounted on it. Let me know if you are interested. I designed and fabbed all the hardware for the LX50. I had the Dec gears from another LX50. The RA gears were from a Nexstar 60 and an old tape player. The control box panel was from a dead Meade DS2000 circuit board.

Attached Files








Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics