Mount alignment a bit strange

[Viv]

Hi all,

I've been working around this, but thought I'd ask.

Firstly, have double & triple checked setting / location / date / time / light savings / level of mount. Balance is not perfect - camera is too heavy, but getting that sorted).

I polar align ok, using a polar cam, can't double myself over, or I fall down with vertigo.

So, then 3 star alignment. First star is always Sirius, have to move the mount (with the synscan). Then whatever the next 2 stars are, the end up centre (or near enough). Controller always states successful alignment.

Anyhow after that whatever I move to, always ends up bottom right of view, not centre !!

Anyone had this, or know what I'm doing wrong ???

It just seems really strange, that the alignment stars are ok, but then nothing afterwards ?!?!

Thanks.

[Viv]

Anyone advise on this please ??

If im being a muppet - please tell me !

I suppose it's every chance, i'm not on Polaris itself, but a close star ?? Mount is to the north & 52 deg .............

[Tribal-Wolf]

You say you always start with Sirius, have you tried other stars to start? Polaris is easy to find but this pic will help.

[Atlas]

Does what your looking for end up in the guide scope at all? I know mine can be a little bit off but it's usually right in the guide scope for easy adjusting.

But it sounds like you did everything right, who knows...I bet the balance and wieght may be the issue.

Have you tried aligning it without the camera and only the eye piece installed yet?

[iwatkins]

Hey Scarlet,

Double check balance and make sure. If it isn't right then even if you get through alignment, your tracking will suck.

The other one, and I've seen it ignored a lot, is levelling. Make sure the mount is level before and after polar alignment and scope balancing. Makes a big difference.

I almost always have Sirius as a three alignment star and it is always miles out as 1st star, usually a good finder scope width out.

But do what I do, follow usual 3 or 2 star lign, get a successful message then drop back into alignment menu and do it again with different stars, seems to really improve accuracy on Gotos. Guess it just needs to build its celestial model.

Cheers

Ian

[Viv]

Thank you all.

I could fairly quickly point to Polaris, but making sure it's the right one in the finder is a completely different thing.

My 3 star alignment always goes to Sirius first. That's good - it's by far the best one, to select first.

I hope the new camera will help with balance, the 1000D is about half weight of the 7D. but the dove bar is already at it's position limit (as in it can't be moved any further along the mount plate - or it'll fall off) !!

Ian - will try that second run - thank you.

[AlBoning]

It is entirely possible what you are seeing is due to cone error. A small mis-alignment between the optical axis of the OTA and the RA axis. Some dovetail mounting plates come with a pair of adjusting screws next to the mounting bolts to correct for cone error. Supposedly the Synscan 3-star alignment accounts for cone error but it could be that it has its limits as to how much can be accounted for. You might be just as well off doing a 2-star alignment. Myself, I just do a 1-star alignment in the neighborhood and another when I go visiting elsewhere. In my case, as I'm using a newtonian, I rotate the scope often in the tube rings and with each rotation the cone error changes. For it not to the optical axis would have to be dead center in the OTA and tube would have to be round ... not going to happen.

Another possibility and the one I'd check first is that the Polar Alignment Scope is not lined up with the RA axis. Check this in daylight by pointing the crosshairs at a distant object and rotating the RA axis. If the crosshairs move off target then it is necessary to adjust the position of the reticle with the three small allen screws. A little goes a long way and there is a possibility that the reticle will drop out of position. There's a multi-media article on this procedure at Andy's Shot Glass http://www.andysshotglass.com/PolarAlignmentScope.html

Finally, for astrophotography it is advisable to do a drift alignment in addition to all that you are doing already. There is another article at Andy's Shot Glass covering how to do this http://www.andysshotglass.com/DriftAlignment.html

[malc-c]

It could be any one or combination of the following:

Cone error

Polar Alignment slightly off

Scope slightly out of balance

Backlash in the gear train.

The first three can be corrected through adjustment, as can the latter to a degree. I guess so long as the target ends up in the field of view of a wide field eyepiece then that's good enough start so that you can use the hand set to bring it into centre.

[Viv]

Thanks Al.

Think it could be clear later, so going to spend one night just looking at alignment & trying different things.

[malc-c]

Thanks Al.

Think it could be clear later, so going to spend one night just looking at alignment & trying different things.

In the meantime, have a look at the astronomyshed video's on youtube. There is an excellent set of setting up, balancing and dealing with cone error etc....might help

[Viv]

Cheers Malc - their videos are really good !!

[Freddie]

A couple of point that I hope will help:

The 3rd star in the alignment process is used to sort any cone error issues

EQ mounts do not need to be level.

[Viv]

Thanks Freddie -didn't know that.

Obviously I make sure they're dead centre, before confirming ok & moving onto the next one ..........

[Black Knight]

Actually it is surprisingly difficult to ensure stars are perfectly dead centre without a reticle eyepiece. Someone posted a link somewhere on SGL recently I think where it discussed this problem and an individuals natural "bias" when it comes to assessing whether a star is perfectly centred or not.

These days I tend to not use an eyepiece at all during alignment. I use my DSLR, and APT's cross-hair reticle in Live View. Leads to much better results and better quality GOTO's in my case.

[Viv]

Actually it is surprisingly difficult to ensure stars are perfectly dead centre without a reticle eyepiece. Someone posted a link somewhere on SGL recently I think where it discussed this problem and an individuals natural "bias" when it comes to assessing whether a star is perfectly centred or not.

These days I tend to not use an eyepiece at all during alignment. I use my DSLR, and APT's cross-hair reticle in Live View. Leads to much better results and better quality GOTO's in my case.

I do use the align selection on backyard to be 100% they are centered, before going to the next one.

Thanks though.

Have allot to try tonight (finger crossed it'll suddenly click (or clow wander) into place).

[James]

Hidden away on Skywatchers website is a note to use a star that's almost due south first of all when aligning. It's also a good idea to use stars around 45 degrees up and as far away from each other as possible in the sky. For some reason Skywatcher and Celestrons handsets often recommend somewhat inappropriate stars for alignments - for example I think Sirius is a little too low, Betelgeuse would be better

Other than that if you are doing alignments and the objects still are appearing in the field of view then you are not doing anything fundamentally wrong, something just needs a tweak

James

[Viv]

Thanks James mate - lol - A little tweak, that sounds much better !!

I'll try Betelgeuse as a first stop tonight.

[Astro_Baby]

Dont centre the alignment star with the main scope, make sure the main scope and its finder are aligned and then use the finders cross hair for alignment. That takes the guessworks out of whether a star is aligned or not to center.

Try it...it works