Making GOTO alignment more precise

[Kirscovitch]

Had the goto for almost 3 months now. Everytime I go out I see and learn something new. But I do have a few questions that I've been thinking about since the last night I was out. 

I know that getting a solid initial alignment is crucial for a goto mount. There are a couple different options I have when choosing my alignment method.

1. Skyalign (choose 3 bright stars)

2. Auto 2 star align

3. 2 star align

4. 1 star align

5. Solar system align

Lately I have been using the auto 2 star. You pick a star from the list, slew manually to get it in the finderscope and hit enter, center it in the EP and hit align. Then it shows a list of other stars to choose from. Pick a star and it automatically slews over and then you have to adjust to get it in the finderscope, hit enter, then center it in the EP and hit align and you're done. From my viewing site at home, I am limited to what stars I can see. Usually I use Sirius for the first one and Aldebaran. Not the greatest combo I'm sure but it is what I have to work with. Now my first question is this: When going through the alignment procedure, when it asks to get the star in the finderscope I usually just get it centered in the EP and then hit enter and align without readjusting. Should I hit enter when it asks and then tweak it like the commands intend before I hit align? Seems to me it just saves a step but does the computer require this to be more accurate?

Secondly, I bought a lighted reticle EP and I really, really like it. No more guessing on where the center of the EP is. It is a 12.5mm and though it is not good for viewing due to the lines going through it, it is wonderful for alignment. Would I get more accuracy if after finding the star in the EP, to quick add a 2x balow and center it with the higher mag?

Just a few things that had me wondering. As of now my alignments are pretty good with the procedure I already have. When I'm done with alignment I usually have no problem finding an object in the EP after slewing to it. Sometimes it is just on the edge but close enough to be able to adjust. But with some of the fainter fuzzies I would like to be more accurate. I was able to see the SN in M82 last week but only after doing a little searching.

[Tinker1947]

Maybe check the PA and get it better than perfect....this could make a difference....

[Kirscovitch]

Maybe check the PA and get it better than perfect....this could make a difference....

If by PA you mean Polar Align I don't think I can with my mount. It's just a single fork alt az. If I can polar align it somehow I have no idea. 

[ronin]

I cannot work out what the second "align" (is there 2 presses for that) does, equally I do not have your scope.

There is also the queastion of does it have a specified start position?

On a Meade the start is everything level and the tube pointing North, in effect this is a virtual star, the scope then does a 2 star alignment. Does mean that the reality is a 3 star alignment. It also allows for what comes across as a 0 star alighment, the scope will operate on the presumption that scope is perfectly level and perfectly North.

I ask about the start position as the scope can get data from where the "ideal" start is to the position of the first alignment star, without this position then no information can be obtained and everything is based on movement fron star 1 to star 2.

I would not bother with the barlow, the time taken to swap and refocus involves time and that longer period could, I think, mean alignment failure.

I would check the handset for a polar/polaris align option. In effect the scope is aimed at Polaris as the start position, then I assumes still does the 2 star align. That bears more resemblance to the Meades as instead of Level+North your start is aimed at Polaris which can be well defined.

What version of software is installed?

[iansmith]

Hello Kirscovitch,

I have the Celestron nextstar 6 which I think uses the same controller as your scope. I too use the auto 2 star align as it is quick and works.

When you move the scope to the first alignment star, the scope assumes you want to move it there quickly to get the star in the field of view of the eyepiece. When you press enter it automatically goes to a slower rate on the assumption that you now want to bring the star to the centre of the field of view. It's easier to do this if the scope is moving slowly. Once it's there you press align to tell the scope that it is pointing at the star. If you can centre the star using the higher slew rate and then press enter followed by align it doesn't matter so long as the star is in the centre of the field of view of the eyepiece when you press align.

Since the scope is on an alt/az mount then there is no need to worry about polar aligning. You have no axis to align on the pole star with. Neither do I think you need to start the scope at a particular position. I never have.

What I have found makes a difference is getting the base of the mount level to start with. A spirit level makes this easy. It also helps if you can put in a reasonably accurate time and location.

Hope this helps you out.

Cheers,

Ian

[Chris Rowland]

Either Auto 2 Star or 2 star.  They both use two stars.  AllSky also uses two stars, the third is to allow identification of the stars.

Use well separated stars, I've got good views to the South so at present will use something like Arcturus and Regulus or Hamal and Procyon.

The two stage approach is because the slew speed is reduced for the align stage.  Use the centre stage to get the star in the telescope field, then switch to the Align stage.

I wouldn't bother with a Barlow with the reticle EP, you should be able to get the star to less than an arc minute without. That's the amount the star moves in 4 seconds when not tracking.

I always finish the final movement using the right and up buttons so backlash is allowed for equally for each align position.

I never bother with levelling the mount accurately and the time goes in to the nearest minute.

All this works for me.

Chris

[Kirscovitch]

Thanks for the tips! There is no "home" position for the scope itself. The Nexstar guide says it doesn't matter what the position is in before you align it. Also I've just been using the level that comes on the mount itself. I do have a small level laying in a drawer somewhere. I'll get it out and try it next time I head out.

I will also try using different alignment stars and see if any combo are more accurate. I am pretty limited to what I can see from the yard, but the star list does give other suggestions.

Also I don't know what buttons I use for the final centering in the EP. I will try the up and right buttons next time.

There is another feature that I have tried as well with not such good results. The feature on my handheld is called precise goto. For example you would enter what object you want. Lets say M33. Then you go into the menu, select precise goto. It then shows a list of nearby stars. You select a star and it slews over to it. You then center the star in the EP and hit enter and it slews back to the original target. 

I have tried this on fainter objects but only have had it work once. That was the night I finally got to see the SN in M82 by doing the precise goto on M81 and jogging over to M82 afterwords.