Aligment - First Star

[Guest]

Hi, nice clear sky last night.

I have an HEQ5 PRO mount with a SW 8inch newtonian scope. When I do the alignment and go to the first star the scope is always miles off target. In the ballpark but quite a bit out. i.e. not even in my red dot finder. So it takes a while to align to that first star. The second and third stars are much better and by the end the alignment is good. It's just that first star. I start the alignment with the scope in the home position as close as I can judge by eye. The polar axis is usually quite good because the tracking is ok.  Is there anything I can do to get that first star closer first time? 

Cheers

Steve

 

[Ronclarke]

I can only suggest balance and a more accurate PA. Do you move your kit around or is it fixed?

 

Ron

[Guest]

Hi Ron, I have to take it out and set it up each time.  Do you know how the scope starts the alignment? Does it assume that the scope is in the home position when it starts? 

When you complete the PA the synscan goes directly to aligment and a few times I've accidentally left the scope in that position when starting the alignment.  In this case the first star alignment is way out.  Then I have to cancel it, put the scope in the home position and restart the alignment. So I assume that the synscan assumes that the scope is in the home position when it starts and that is the zero point for the encoders. I guess if I can get the home position more accurately that should help.

Once I've completed the alignment everything is fine. It finds the targets I select pretty well and it tracks ok too.

Steve

 

[Owmuchonomy]

The symptoms you are describing are not unusual. Sounds like the alignment is working ok after 2 or 3 star alignment. Synscan does assume your mount is reasonably polar aligned (doesn’t have to spot on) and that the OTA is in the home position. You may find you have some cone error. Which is working best 2 or 3 star alignment?

[Neil H]

Hi if you go to the thread on fine tuning of synscan there is an option in the handset to turn off and this helps set up , but when you finish for the night make sure you park the scope so you start each time in the home position

Mine  is off on first star but it may be my setting  up as i can't  see Polaris at all 

 

Edited March 16, 2020 by Neil H

[Jiggy 67]

You are right, an accurate home position does assist accurate star alignment as does an accurate polar alignment. See this video on how to get an accurate home position, it’s worth the effort to get it right 

https://youtu.be/4fO6hyYtPwM

Also an illuminated reticle eyepiece is a good idea for accurate centering of the star

 

Edited March 16, 2020 by Jiggy 67

[CaptainShiznit]

If you are imaging or intending to image you might find this useful. I was happy to leave all this behind using APT and plate solving.

After polar alignment, you can use APT to slew to where you want, plate solve, sync and slew again. You can even use the GoTo++ function and it'll do it all automatically usually in under a minute and have your target perfectly centered. Once I discovered this, there was no going back to using the handset and star alignment.

[Ronclarke]

I don't understand why you have to move the scope when Polar aligning? It's the mount that is aligning not the scope..

As long as the scope is in the home position from your previous session it should not be to far out on the first star..

I now use the SynScan Wifi adaptor as I find it more accurate than the handset!

Cheers

Ron

[Guest]

You have to rotate the RA axis to get the polarscope reticule in the right orientation. The mount is not then in the home position. Sometimes I forget to return it to the home position before I start alignment. Then the first star is way off. Apologies for using wrong terminology. I sometimes use the terms scope and mount interchangeably.

Thanks everyone. Some useful stuff. I've now marked up the mount with what should be a more accurate home position. I've also got a few other ideas about it but I need a clear night to check.

Thanks again

Steve

 

[Ronclarke]

Glad we sorted that Steve,  forgot moving the RA to use the polarscope as I use an iPolar device..

Good luck and clear sky's..

Ron

[Neil H]

Steve let me know how you get on please if it works for you and you get really good alignment on first star may be you can share what you did 

[Guest]

Will do Neil. Just need a clear night.

One idea I had was to do with the timing of switching on the mount. I think the mount resets its position when you turn it on. One thing I think I was doing wrong was that when I get the thing out of the shed and set up on the yard I haven't been at all careful about the position of the mount when I switch it on. It's usually very roughly in the home position but because I know I will have to move it in order to do the polar alignment I don't bother with it. So I do the polar alignment, put the scope in the home position (manually) and start the first alignment. But the position of the two axes has already been reset right at the beginning but not very accurately. Also, when I rotate the RA for the polar axis alignment I've been doing it manually not through the hand set. So now the scope is doubly out of wack - if you see what I mean.

So my new sequence is like this -

1 Switch on the mount

2 do the polar alignment

3 Switch off the mount

4 Put it in the home position as accurately as possible

5 Switch it on

6 Skip through the polar alignment (since I already did it)

7 Start the alignment

We'll see.

Cheers

Steve

 

[Guest]

I tried this last night and it worked pretty well.

1. Mark up the mount's RA and DEC axis with the home position. There are several videos quoted above which tell you how to do this. You only have to do this once.

2. Do the polar alignment in the normal way.

3. switch off the mount.

4. Manually move the mount to the home position as accurately as possible.

5. Switch the power back on. You'll have to put the time and date in again. Skip the polar alignment.

6. Select 1,2 or 3 star alignment as you wish.

There you go.

Last night the scope went to the first star fairly accurately. It was in the eyepiece anyway which was much better than before.

At the moment I still do the polar alignment using the handset. 

Cheers

Steve