Alignement accuracy inconsistency with SkyWatcher EQM-35 PRO GoTo

[Samibotss]

Howdy,

I've been imaging the Eagle Nebula (M16) over the past few weeks, and I've encountered a problem concerning alignement accuracy as of recent. Simply put, on some nights I'll be able to get a decent alignement and have the mount find the object on the first try, and on others like tonight, using the same stars, the mount just doesn't seem to hone-in on the object.

It's strange, as I'll often test the accuracy after having done my 2-star alignement, and it finds objects like planets and bright stars relatively accurately (if only off-center), but fail to hone-in on M16. Unfortunately, I have a limited view of the night sky, and can only use stars in the south west - south east region, so I have a limited range of stars to be used for alignement, but even trying other stars doesn't seem to solve the problem.

Should I go for 3-star alignements? Is there something I can do to fix this? What's even more problematic is it seems sporadic, as if the mount wants to cooperate on some nights and doesn't on others.

Any help is appreciated

[ONIKKINEN]

The pointing accuracy of my EQM35 was never all that good, and it did also seem to have its own mind on when to be less good than other times. But you can make things easier with a couple of things.

5 hours ago, Samibotss said:

Unfortunately, I have a limited view of the night sky, and can only use stars in the south west - south east region, so I have a limited range of stars to be used for alignement, but even trying other stars doesn't seem to solve the problem.

Should I go for 3-star alignements? Is there something I can do to fix this? What's even more problematic is it seems sporadic, as if the mount wants to cooperate on some nights and doesn't on others.

Yes, you should try to do 3- star alignments with the mount and it will imrpove the accuracy a bit, but the problem here might be that you have a limited sky to pick the alignment stars from. 3-star alignment ideally will use 3 stars that are at very different parts of the sky, something that might not be possible for you.

A trick that you can do is do the 2-star (or 3, or whichever) alignment as you normally would and then do a final extra 1-star alignment on a star that is close to the target you will image that night. That will increase the accuracy further and if you manage to find an alignment star within the general area of the target you will pretty much always land the go-to afterwards. With the eagle nebula you could use Altair, which is pretty close. This is what i did before i did platesolving.

Which bring me to another question. Do you platesolve, if not, why not? Looks like you have guiding so you have all the indgredients needed to platesolve (just a computer basically). With platesolving your setup will auto-center itself to the target and you dont have to do the star alignments at the start of each night anymore.

[Steve Ward]

Accuracy regarding the Time inputted is a factor often overlooked , and the time spent faffing about after putting the time in the handset can throw things off.

A couple of minutes equals half a degree on top of anything else.

[Samibotss]

3 hours ago, ONIKKINEN said:

The pointing accuracy of my EQM35 was never all that good, and it did also seem to have its own mind on when to be less good than other times. But you can make things easier with a couple of things.

Yes, you should try to do 3- star alignments with the mount and it will imrpove the accuracy a bit, but the problem here might be that you have a limited sky to pick the alignment stars from. 3-star alignment ideally will use 3 stars that are at very different parts of the sky, something that might not be possible for you.

A trick that you can do is do the 2-star (or 3, or whichever) alignment as you normally would and then do a final extra 1-star alignment on a star that is close to the target you will image that night. That will increase the accuracy further and if you manage to find an alignment star within the general area of the target you will pretty much always land the go-to afterwards. With the eagle nebula you could use Altair, which is pretty close. This is what i did before i did platesolving.

Which bring me to another question. Do you platesolve, if not, why not? Looks like you have guiding so you have all the indgredients needed to platesolve (just a computer basically). With platesolving your setup will auto-center itself to the target and you dont have to do the star alignments at the start of each night anymore.

I didn't know I could do multiple alignements, I always thought doing an alignement would wipe the previous one's data. I'll try doing 2-star + 1-star and see if it improves result.

As for platesolving, I just never took the time to learn it and understand it, will surely check it out now that you mention it

2 hours ago, Steve Ward said:

Accuracy regarding the Time inputted is a factor often overlooked , and the time spent faffing about after putting the time in the handset can throw things off.

A couple of minutes equals half a degree on top of anything else.

Yeah I thought of it as well, so I parked and restarted the mount, but alignement was still off...

[scotty38]

Agree with the above, platesolving will change your world 🙂 🙂