GEM alignment for EAA

[aparker]

I was reading Don's new LL user guide (which is excellent), and his discussion of mount alignment prompted me to mention how I've come to do it. I used to do the alignment visually with an eyepiece, then swap in the camera. I am BTW using a Celestron CGEM, but most consumer GEM have similar alignment routines.

What I have started doing, which works really well, is this.

1. I have built a "pier" of sorts on the deck where I observe, so I can set the mount head out in exactly the same position night after night. Not essential, but a time saver over setting up the tripod de novo every time.

2. I have mounted a cheap Orion guidescope (170mm FL) on my SCT, along with an Orion guide camera. This has the same size chip as the Lodestar, but is of fairly poor quality. That does not matter as it is only used as a finder. I carefully tweaked the guidescope mount so it is coaxial with the main scope, to the finest degree I can accomplish.

3. When I go out to observe, I hook up the guider to PHD2 (free guiding software), and the main camera (Lodestar or Ultrastar) to LL (now Starlight Live). At this point I never use PHD2 to actually guide, but I like having the option for the future.

4. On both applications, I put a crosshair on the image window (in FF mode for SLL).

5. For each alignment star, I first coarse center using the Orion, which has a wide enough FOV that I never have to hunt for the star - it's always in the field. Then fine center using the Lodestar, really being careful to put the star as exactly as I can in the dead center of the crosshairs. It's worth getting it perfect, like under 0.5 arcmin.

6. With the CGEM, I do a two star alignment, then add two calibration stars (other mounts may have different functions like "sync to object" to allow this latter).

This procedure is easy enough that I now have removed all visual guidescopes/red dot finders from the telescope and use it ONLY electronically, through these two sensors. By combining this with some very careful balancing of the scope (with setup points now marked with Sharpie on scope and mount for reproducibility), I now get <5 arcmin accuracy on gotos over the whole northern sky (can't see much south of the zenith from my observing spot). This has been tremendously helpful when looking for faint objects that can't be seen at all with less than several stacked 10 sec shots. I never have to hunt objects now - they are always in the FOV, usually so close to centered that I don't bother tweaking the pointing, just start observing.

Short of having a dedicated observatory with a scope that is never taken down, I think I have done about as much as I can do to make polar alignment and object finding/tracking easy, and the work has paid off tremendously for me in terms of time and headaches saved when I have that rare combination of free time and clear skies.

Anyway, thanks for reading, and hopefully these ideas are helpful to the rest of the community here.

[HiloDon]

Alex,

Thanks for the great alignment tip. I'll add it to the next version of the guide.

I do something similar with my Atlas mount, although I just use a visual finder. The finder is aligned accurately with the main scope that has the Lodestar. I visually center the finder on the alignment star, then fine center it in the focus assist window in LL. Your procedure also eliminates the need to refocus when switching out the eyepiece. The switch usually throws the alignment off a bit, too.

The Lodestar and LL focus assist window can also be used for drift alignment to get good polar polar alignment. There are plenty of references out there on drift alignment. I would recommend to anyone using an EQ mount to polar drift align. It's really easy and doesn't require a view of Polaris.

Don

[aparker]

Don,

That's a great point that I overlooked. When first optimizing my mount positioning on the pier, I used the builtin drift align assistant in PHD2 to get it dialed in. Very useful technique.