Yet another mount issue.

[Jnicholes]

Hi everyone,

Once again, I have a mount issue. In fact, I have finally noticed a pattern with it.

Let me give you the rundown. I do an auto two star align, and I align to Polaris first. Then, I align to another star on the opposite side of the sky, in this case, Sirius. Once it aligns successfully, which it does do, I go to the Orion nebula as a test. After successfully going to the Orion nebula, I try going to a different object, like the Pleiades, or the Andromeda galaxy.

It does not go directly to these objects. In fact, it doesn’t get to them all the way. It is way off when it tries to go to other objects. I will do some math and tell you exactly how off it is.

I have actually noticed a pattern, which makes me believe that there is a glitch in the system of my mount.

For the past 2 to 3 years, this problem has arisen every year from January to April. In fact, this is the reason I missed seeing comet Leonard.

After April, the problem disappears.

This is a mystery now. Is there any idea what the problem is?

I will get back when I do the math to tell you exactly how many degrees off I am.

Jared.

[Jnicholes]

Never mind, I finally fixed it. After figuring out what the pattern was, I concluded that the telescope was not being aligned properly in winter. I just went out, I did the exact same alignment procedure I did last night, and it’s working fine.

I feel sheepish!

[Lady Fraktor]

I assume this is the GT mount?
Try not to use Polaris as a alignment star. it can actually screw up alignments.
Its a Celestron mount thing unfortunately.

Have you ever set the backlash on this mount? It also adds issues with goto precision.

[Greenman]

I assume this is the GT mount?
Try not to use Polaris as a alignment star. it can actually screw up alignments.
Its a Celestron mount thing unfortunately.

Have you ever set the backlash on this mount? It also adds issues with goto precision.

Try not to use Polaris as a alignment star. it can actually screw up alignments.
Its a Celestron mount thing unfortunately.

Not done that, but thanks for the heads up!

[Jnicholes]

Good morning, everyone.

Thanks for the advice, I appreciate it. I will try not to use Polaris in the future.

Regardless, I did get it to work last night by aligning to Sirius first, then Polaris. It was able to accurately go to every object I input.

Jared

[JayTee]

Just to add my two cents and agree with Gabrielle, I never use Polaris as an alignment star for any of my Celestron mounts.

[Jnicholes]

Just out of curiosity, why should I not use Polaris?

I was under the impression that if you used a star that was “stationary“ like Polaris and another star, it would easily calculate where all the other stars are at. Was I mistaken?

Anyway, here’s something else I’m going to add. Is the exact rundown of last night, when I was able to get it to work.

Got the telescope out side. I plugged it in. I selected auto two star align. I set the exact time and date. I aligned to Sirius first. I selected Polaris as the second star. The Telescope moved to Polaris. It did not point to Polaris exactly. I adjusted the telescope using the controller to center and align Polaris. After aligning Polaris, I did a test of the goto function and went to M42. Went straight to it. M 42 was slightly to the right in the eyepiece. Afterwards, I did another test and decided to go to the Pleiades cluster. After inputting, the telescope moved to the Pleiades with no problem. Then, I went to M31, the Andromeda galaxy as another test. To my surprise, it went straight to it. I was anticipating that it would miss, like it usually does this time of year. I then did another test, and went to M33, the Triangulum Galaxy. It went straight to it, but I could not get a picture because of windy conditions. I then selected a planet to go to, Jupiter. It went there no problem.

The only thing I did differently between the night that it did not work, and the night that it did work, was that I auto two star aligned to Sirius first, then I aligned to Polaris. The night it did not work, I aligned in a different order. Polaris first, then Sirius.

When I tracked C2022 E3, I aligned to Dubhe and Polaris.

I just now noticed some thing.

I don’t know why, but all those other nights in 2021-2022, when I aligned to other stars, not including Polaris, it did not work January to April. Now, it’s working just fine. The only thing I’m doing differently is that I am auto two star aligning to Polaris and another star.

That’s all.

Jared

[Jnicholes]

OK guys, I just had a brilliant idea.

My camera is able to take video, so I will take a video through the telescope and try to show you the problem. I will show you exactly how I am aligning, and I will see if I can replicate the problem.

[Lady Fraktor]

Sometimes it is a combination of things, backlash not set, using Polaris and time to align.
With these Az/Alt mounts tracking is not active while centering aligning stars.

I will pick my alignment stars before starting so I can quickly go from west to east then up/ east (using up & right on approach)
The faster you can align the better the accuracy.

[JayTee]

If you have figured out a way to make your alignment work, we don't necessarily need to see a video showing the "wrong" way.

As a rule of thumb, I always choose my alignment stars as far apart as possible. Typically from NW and SE, or the SW and NE quadrants. Right now I would choose Mirfak in the NW and Sirius in the SE at 8:00 PM in the evening.

The bigger the separation between your alignment stars, the more accurate the calculation on the "sky model" IMO. The very first slew after the goto alignment is right back to the first alignment star to see how it shows up.

Remember, always and I mean always, make your final slews to the alignment star RIGHT AND UP to get to the center of the FOV! This is the motion the mount uses when slewing (unless you've changed that).

Hope these tips help.

[Jnicholes]

I want to thank you all for helping me out and for being patient with me. I really appreciate it.

The problem cropped up again tonight. I was able to take a detailed video of what happened.

Could you all please take some time and watch this video? It shows exactly what I am doing and what the problem is.

https://www.youtube.com/watch?v=wFJmXwBsTZg

Thanks again,

Jared

[JayTee]

Okay, some things I need to know. The video does not tell me what your problem is, the answers to my questions just might.

Thing one, did we ever establish which Celestron goto mount you are using? Is it the SLT, or the GT, or the LCM?

Thing 2, do you have a way of knowing the exact center of your camera's FOV. For example, SharpCap allows you to put a bullseye overlaid over the image so that you know where the center of the FOV is. Do you have this function for whatever software you're using for your camera? If you do not have the center of the FOV illuminated then getting an accurate goto alignment will be problematic.

Thing 3, your iPhone sensor is the equivalent of a 6mm EP. Asking your goto mount to center up an object in such a small field of view is unrealistic. The fact that it got close to the Orion Nebula after your first slew back to it tells me that you're alignment was fairly close.

Thing 4, always make sure your first slew after a successful goto alignment is back to the first alignment star so you can see how well it's doing.

Please let me know about these things.

[Jnicholes]

OK, here are the answers.

First, I don’t know exactly what type of Celestron mount it is. I bought it off of eBay, and the seller never specified what type of mount it was.

Second, I don’t have a way of figuring out the exact center of the field of view. However, I can look into figuring that out. That could be part of the issue.

I thought I was pretty detailed in the video explaining what the problem was. Was I mistaken?

[KathyNS]

Just out of curiosity, why should I not use Polaris?

Polaris doesn't move enough.

Aligning on a target that moves a lot will give you very accurate information. A 1 arcminute error aligning to an object on the equator corresponds to an error of 1 arcminute of RA: quite small. On the other hand, a 1 arcminute error aligning on Polaris could correspond to an error of up to 1.27 degrees in RA, because of the converging lines of declination.

[Lady Fraktor]

I believe we determined a while ago that the mount was a GT?
They look like a SLT but does not have the on/ off switch.

[Jnicholes]

I have a hypothesis on what the issue is. I’m going to test it tonight, then report back.

[JayTee]

I thought I was pretty detailed in the video explaining what the problem was. Was I mistaken?

Yes, you are mistaken.
What you gave us is visual accounting of what's going on, of which your alignment seems reasonable, you made it to 4 out of 5 targets. What we really need is a procedural accounting of what you are actually doing.

Next time, do your alignment with a 10-12mm EP. After a "successful" alignment put in your lowest power EP to see if your intended object is that FOV. If it is, you've done well.

Lastly, do you know how to use the "sync" function of your mount?

If you do not have a reticle EP in your arsenal, you should.

[Jnicholes]

I thought I was pretty detailed in the video explaining what the problem was. Was I mistaken?

Yes, you are mistaken.
What you gave us is visual accounting of what's going on, of which your alignment seems reasonable, you made it to 4 out of 5 targets. What we really need is a procedural accounting of what you are actually doing.

Next time, do your alignment with a 10-12mm EP. After a "successful" alignment put in your lowest power EP to see if your intended object is that FOV. If it is, you've done well.

Lastly, do you know how to use the "sync" function of your mount?

If you do not have a reticle EP in your arsenal, you should.

I have to say right now, I feel very frustrated. I thought I was pretty detailed in the video. The fact that I was mistaken really frustrates me. I spent an hour last night trying to get the telescope to work, and in the last 10 minutes, that’s when I made the video. I was hoping it would help out, but apparently it didn’t.

Maybe frustrated is an understatement, actually.

Keep in mind, I’m NOT frustrated at you, I’m just frustrated at the facts.

I need some time to cool down, if you know what I mean. I will post later.

Jared

[JayTee]

Keep in mind, I’m NOT frustrated at you, I’m just frustrated at the facts.

I completely understand! These goto mounts will on occasion cause you to lose ALL your hair -- because you pulled it all out!

The reticle EP will help. Using a very low power EP to assess your goto accuracy will help. Lowering your expectations on how accurate was your goto slew, will help.

Remember always using RIGHT AND UP as your final slew motions to your alignment star will help.

Those of us who have been doing this for a while know that on any given night, your slews with an entry-level goto mount can be spot on or miss by as much as 1-2°. And you didn't change how you do your alignment! It's just the nature of the beast.

Sorry, you're going through this, but I guarantee you'll know the very best way to do a goto alignment when this gets solved!

[Jnicholes]

OK, I have cooled down sufficiently.

It is also clear tonight. I am going to go out again, and this time, I AM going to make a video, but I will not upload it. I’m only doing this so I can vocally keep track of everything that I need to document until I can write it down. (It’s an ADHD thing.)

I’m going to use the same set up that I used last night (except for the focal reducer, which I hypothesize is making it more difficult to align,) and document everything that I do and notice.

I will do it with multiple alignment attempts.

@JayTee will this be sufficient? Is there anything I should add to what I should do?

Of course, I will take your advice that you’ve given me so far.

Jared