Chapter 4 of Michael Swanson’s “The NexStar User’s Guide II” is entitled Alignment and is the chapter that made me want to buy the book and read it cover to cover. Readers of the blog know that I struggled with alignment for my NexStar 8SE (Solving alignment problems with the Celestron NexStar 8SE) and Michael’s online resources were helpful in resolving some of them, or at least narrowing the problem. I even held off buying the book because he said Guide II was coming and I should wait over Guide I. Then I managed to solve most of the alignment issues, and so when his book arrived, I didn’t devour the whole book right away. I just cruised through the Alignment chapter. Then this past summer, I went back and re-read everything in order.
Here are some highlights from Chapter 4:
Backlash compensation (P.87): A great element for those of us with slightly older scopes whose mounts are no longer “factory fresh”. My son’s new 4SE? Dead tight regardless of the direction I’m slewing. My 8SE? There’s a bit of a lag. I tried adjusting this 3 years ago and just got confused. The new guide has it very clearly laid out, and I’ll be attempting a fix later this month.
GoTo Approach (P.88): Tied to the backlash compensation is a setting that depends on whether your scope is back-heavy or front-heavy. I have always felt that my scope was “front-heavy” the way I pushed it forward, but I reached out to the author to ask, and he confirmed that the SE series is still generally back-heavy given the weight of the mirrors, unless you are using a metal dew shield to make it more front-heavy. I need to change this too.
At the time of this writing, the default settings for the NexStar+ and the SkyPortal app are negative for altitude (up/down). The default settings for the NexStar version 4 and StarSense hand control are positive for altitude. When used in alt-az mode (no wedge), back-heavy scopes perform best with this set to positive, while front-heavy scopes should have it set to negative. This helps to minimize the effects of gear backlash on GoTo accuracy.
Accurately Center Alignment Stars (P.89): The end of the section outlines the doughnut method for doing alignment, i.e. defocusing a star until it is a large disc that makes it easier to see how well it is centred in the eyepiece/field of view, a great method.
Final Movements When Centreing Alignment Stars (P.89/90): Regardless of backlash compensation, or your GoTo Approach above, the scope is always going to have its drive tighter in two directions than the other two. In other words, for azimuth at least, going right is always going to be tighter than going left. When you go left, there will always be a bit of slippage. So you always want the “last” movements when centering to be to the right to keep the drive as tight as possible, no slippage. Any slippage will increase your margin of error with the alignment.
The PROBLEM comes with the up/down movements. And the source of multiple years of alignment problems that I couldn’t figure out for the life of me. All the online tips say that the final movement should be: Right and Up. In other words, the tightest last movement should be to the right (as above) and then up. In theory, this means that DOWN will have slight slippage, UP will be tight. And that’s what I was doing.
Except I wasn’t. Here’s the bombshell from the guide:
To help minimize the effect of gear backlash, your final movements when centering the alignment stars are essential. The default settings with the NexStar+ hand control and the SkyPortal app require you to center each star with final movements using only the right and up arrow buttons. The default settings with the NexStar version 4 hand control require you to center each star with final movements using only the right and down arrow buttons.
While the bolding is mine, I would like to THINK that if I had read that, I might have saved myself a few years of pain. My handset did indeed have the settings reversed — so I was doing “RIGHT AND UP”, but my handset was inverted, and I should have been doing “RIGHT AND DOWN”. Son of a biscuit. Which meant that while my azimuth settings were relatively fine (left and right were tight), my altitude was consistently off. Only when I was talking to the guy who programmed the hand controller one night and I mentioned that the setting was inverted did we together have a eureka moment. Every single site I found online, every reference, everything I saw said NexStars should go RIGHT and UP. It never occurred to me that my default settings were different. I have no idea if I had read that bolded section above if my brain would have sparked or not. It sparked when I was out with the programmer trying to solve my alignment issues. Alas, I read it in the guide almost three years later. Grrrr.
Cancelling a Slew (P.91): This is one of the most useful things I learned in the whole book, and it is so simple. Once you press enter on the hand control when selecting an object to view, the GOTO features take over and it starts slewing there. I’ve tried hitting BACK, a few other buttons, nothing seemed to stop it until it got to its destination. One time that was a zenith location and my diagonal was hanging down low, and yep, it smacked the mount base. It ground so hard, I needed Celestron to fix it and my mount was gone for 2 months. I got to this section, and literally I was like, “Are you kidding me? All I have to hit is one of the directional buttons? Really? How did I *not* figure that out before?”. Sheesh.
Various alignments (P.92-99): While I feel that I knew most of the details about Sky Align, Auto Two Star Align, and Two Star Align, mostly from reading various posts online (some by the same author), I knew very little about One Star Align or a Solar System Align. I’m itching to try the Solar System align to see if I can do some stuff during the day (with appropriate solar filter in place, just in case it passes the Sun). I confirmed with the author I can even do this on the Moon or the Sun. Woohoo! 🙂 Maybe I’ll try it the day of the Mercury transit this year (November 11th) as I’ll be outside anyway!
Using SkyPortal (P.99-103): I have the wifi dongle, and I have found the connection with the tablet or smartphone to be a bit finicky at times. Nevertheless, I am inspired to try it again, partly because I hadn’t realized you could add more stars to the alignment process — up to 10 in total to improve GoTo and tracking. I desperately want to try that. I’ve thought of buying a StarSense for improved alignment, but I am willing to try this first. Might want to upgrade firmware though.
I have always wondered what stars are in the database for possible use during alignment, and a DLable manual on the author’s website notes that
- Two Star alignment has 247 possible objects [a somewhat eclectic list, as some go as faint as 5.4 (Polaris Australis) but even a full list of magnitude 4 would well surpass 250 objects];
- Auto Two Star and One Star are limited to 56 possible objects (again, a bit odd since there are 88 constellations and you would think at least the brightest in each would be available); and,
- Sky Align (the generic three star approach) has 82 possible objects.
And here’s the weird part…you would think it would be cascading / shrinking lists — 247 for 2-star, 82 of those for Sky Align, and 56 of those for Auto 2-star or 1-star. Except Albireo and Algenib are available for 2-star and 1-star but not the more general Sky Align. Albireo is a double-star, but there are other doubles in the list (Mizar, for example); I don’t know what’s unique about Algenib. Like I said, weird. I assume it has something to do with the math for Sky Align, some sort of conflict if you use those two.
Sync (P.123): I had learned how to do this, as well as Precise GoTo (P.124), when I was out observing with the hand controller programmer, but it was good to see how to use a semi-permanent “additional alignment star” for a series of viewings or a local star for a one-time alignment boost.
One thing I have never seen listed anywhere (and it’s not in the guide) is what to do when something happens and your alignment changes during the night. You can replace alignment stars, sure, but my question was more specific — what happens if you “kick” the tripod by accident (or more likely someone passing by kicks it) — do you reboot the scope and start over? There’s no menu option to start a new alignment from the beginning. I reached out to the author of the Guide II to ask. He confirmed that while you may have to do a reboot if the legs are moved considerably (i.e., the alignment may fail when you do the first replacement), you can always try just repeating the existing stars again rather than starting fresh or saving two new alignment stars. Good to know.
And this concludes Chapter 4. This chapter alone was worth the purchase price.