Sky Watcher 130PDS Collimation

[Jamgood]

13 minutes ago, Pixies said:

No problem! It was good to get my understanding of it down on 'paper'. I made some mistakes when I got my new scope and nearly mucked things up well-and-truly!

 

Geez! At least you managed to sort it out.  I don't think I'd know where to begin on your problem.  That would've been a total nightmare for me.  Interesting to see you mention Bobs Knobs in that thread. I could have used some of them over the last two days instead of messing around with a tiny allen key. One day I'll upgrade them

[Pixies]

1 minute ago, Jamgood said:

Geez! At least you managed to sort it out.  I don't think I'd know where to begin on your problem.  That would've been a total nightmare for me.  Interesting to see you mention Bobs Knobs in that thread. I could have used some of them over the last two days instead of messing around with a tiny allen key. One day I'll upgrade them

Don't. You can buy them cheaper on Amazon. Mine were replaced by:

Or just buy the caps to go over stainless steel hex-headed machine screws. Someone more familiar with your scope will be able to give you the sizes required. See: 

 

[Jamgood]

Got the Cheshire today. I wasn't far off with my homemade cap. I think this tool is going to make it a lot easier though. A little tweaking here and then on to the primary.

Edited July 22, 2020 by Jamgood

[Apprentice]

16 hours ago, Pixies said:

Don't. You can buy them cheaper on Amazon. Mine were replaced by:

 

 

Hi @Pixies This looks like a good replacement for secondary collimation screws, mind if I ask if you already received them (use them)? I am thinking of buying this for my scope its 5" newt, so I am htinking the 30mm would suffice.

 

[Pixies]

Just now, Apprentice said:

Hi @Pixies This looks like a good replacement for secondary collimation screws, mind if I ask if you already received them (use them)? I am thinking of buying this for my scope its 5" newt, so I am htinking the 30mm would suffice.

 

Mine is a Bresser 8". You will need to find out the size of the current secondary adjusters. Take just the one out (horizontally, mind you!) and measure it up. These will need to be a little longer, obviously.

 

If you want just some hex-headed machine screws, to add your own cap, message me, as I have quite a selection and I'll send you 3 for postage costs. if I have the right size.

[Jamgood]

I'm ready to give up on this and send it back, try my luck with something else. The Cheshire is useless as it sticks out too far the mirror to be able to see to align anything. I thought I'd be able to slot it in the tube further but SkyWatcher haven't supplied anything that will work that way.

I keep spending money trying to fix this thing and I haven't had a single minute of enjoyment yet, just stress.

I've messed it up completely today but when I put the Cheshire in, it looks different everytime because the focuser is renowned to be rubbish.

 

Edited July 22, 2020 by Jamgood

[alacant]

2 hours ago, Jamgood said:

it looks different everytime

Hi

It maybe that the primary mirror is moving rather than the focuser. Or the secondary is loose or missing a spring. Maybe the primary adjusting screws have come off the end of their thread... Loadsa stuff it could be e.g. I had to fix my primary to the cell with silicone 'glue' before it would hold collimation.

As it is, it will work, but you'll lose faint detail and the stars won't look good.

Assuming you've got the secondary more or less in the centre of the tube, insert the Cheshire with the focuser at the same position as where your camera/eyepiece focuses. This way, you'll collimate out any the tilt. Adjusting the secondary only, get the Cheshire cross hairs on the primary donut first. Or at least somewhere near. Then leave it. Now adjust the primary until it's concentric. Now move the telescope. Does the collimation stay?

If you want it for astrophotography, best to dismantle and reassemble, especially the 1º mirror cell. The focuser can be adjusted too but remember, at this price point, you're gonna have to do some work to get it up to the necessary standard.

Before you give up - and remember that it's always best to leave stuff like this 'till the next day- be sure to read the collimation myths. It's a lot easier than you think:) Below, I've put the current state of play.

Good luck and do tell us when (sic) you have it fixed.

Cheers, good luck and HTH.

Edited July 22, 2020 by alacant

[Jamgood]

1 hour ago, alacant said:

Hi

It maybe that the primary mirror is moving rather than the focuser. Or the secondary is loose or missing a spring. Maybe the primary adjusting screws have come off the end of their thread... Loadsa stuff it could be e.g. I had to fix my primary to the cell with silicone 'glue' before it would hold collimation.

As it is, it will work, but you'll lose faint detail and the stars won't look good.

Assuming you've got the secondary more or less in the centre of the tube, insert the Cheshire with the focuser at the same position as where your camera/eyepiece focuses. This way, you'll collimate out any the tilt. Adjusting the secondary only, get the Cheshire cross hairs on the primary donut first. Or at least somewhere near. Then leave it. Now adjust the primary until it's concentric. Now move the telescope. Does the collimation stay?

If you want it for astrophotography, best to dismantle and reassemble, especially the 1º mirror cell. The focuser can be adjusted too but remember, at this price point, you're gonna have to do some work to get it up to the necessary standard.

Before you give up - and remember that it's always best to leave stuff like this 'till the next day- be sure to read the collimation myths. It's a lot easier than you think:) Below, I've put the current state of play.

Good luck and do tell us when (sic) you have it fixed.

Cheers, good luck and HTH.

Part of the problem, as I see it, is when you put the Cheshire in the focuser, there are only 2 locking nuts and they push the cheshire off to an angle. Does the same with a camera but the angle, each time, is never consistent. So what looks lined up changes when you go back to it.

The Cheshire being so far away from the secondary doesn't help me at all. Looking through the tiny hole, everything is black. (I can't put the Cheshire in the focuser tube)

So with the above I'm having to rely on taking a photo with my phone,  (god knows how reliable that is) email it to myself, check with the crosshairs in the collimation app. Rinse and repeat. 

What was looking all line up yesterday didn't work. I did some quick snaps of stars in a gap in the clouds last night. Couldn't get any focus at all. Sharpest was blurry and everything else was D shaped. I'm not sure if that's to do with the secondary mirror as when it is as close to circular as I can get it, it has a flat edge. 

The hardest part is that I'm not really sure what I'm doing. I'm learning as I go but no way would I be removing mirrors and stuff like you're saying. That's a sure fire way of making it completely destroyed. I'm not that handy.

I think the thing is defective.

[alacant]

16 minutes ago, Jamgood said:

D shaped

You need to cut around 10mm from the end of the focuser barrel. You can see how it intrudes into your light path in your photo.

16 minutes ago, Jamgood said:

no way would I be removing mirrors

NP. Just take it along to a local astro club. They'll tell you if it's defective, or fix it, and even say thank you for letting them have the honour! My money is on the latter;)

I think you've just got another case of SkyWatcher's non existent quality control. 

Cheers

Edited July 22, 2020 by alacant

[Jamgood]

I'll start from scratch again and see if I can get it anywhere near. 

[Jamgood]

Everytime I get this part to a near perfect circle I end up with a flat edge. (Top right quarter) Any adjustment from there and I seem to lose the circle and go round in circles, literally.

[Pixies]

Hi,

Sorry it hasn't been a success, today. Yesterday looked so positive!

It's odd how that flat spot doesn't appear in the silhouette. The secondary mirror is quite large though, so as long as you can see the whole of the primary in it, that shouldn't have an effect. Can you see whether the whole of the primary is visible over the whole range of the focuser?

Alacant says - you can see the end of the focuser tube when it is fully in. As long as you don't need to get in that position when focussed, that shouldn't matter. Mine is similar.

Try A's suggestion and get it as close to collimated as you can, then move it to various extremes on the mount and see whether it stays in collimation.

It might be worth putting a call-to-arms for the 130PDS owners in the general equipment forum, with an obvious title, like: "130-PDS owners - help!" and direct them to the end of this thread.  Someone might have seen this issue before.

Have you spoken to the supplier?

 

P

[Jamgood]

37 minutes ago, Pixies said:

Hi,

Sorry it hasn't been a success, today. Yesterday looked so positive!

It's odd how that flat spot doesn't appear in the silhouette. The secondary mirror is quite large though, so as long as you can see the whole of the primary in it, that shouldn't have an effect. Can you see whether the whole of the primary is visible over the whole range of the focuser?

Alacant says - you can see the end of the focuser tube when it is fully in. As long as you don't need to get in that position when focussed, that shouldn't matter. Mine is similar.

Try A's suggestion and get it as close to collimated as you can, then move it to various extremes on the mount and see whether it stays in collimation.

It might be worth putting a call-to-arms for the 130PDS owners in the general equipment forum, with an obvious title, like: "130-PDS owners - help!" and direct them to the end of this thread.  Someone might have seen this issue before.

Have you spoken to the supplier?

 

P

It does have to be zoomed in quite a way for focus to be achieved. (Usually making PacMan shaped stars) The focuser tube does protrude and that I expected from what I'd read about the scope before buying. I know a lot of people cut the tube down or move the primary up the tube, losing focal length but not having to butcher the focal tube. From what I read, there's a certain Coma Corrector that has enough back focus to omit doing either of those. That's what I planned on getting.

I used the phrase D Shaped stars but they were more like arrows. Starting from the outside, pointing inwards towards the centre. Like they are out of focus but the centre star is bang on. Almost like drift but all drifting different directions.

When I insert the camera to the focus, the two grubs screws force the attachment to an angle. either up or sideways. So what I've done tonight is force the Cheshire in the same direction and (hopefully) collimated it. Out of interest and frustration. I spent an hour or so on the laser collimator, took it to bits, straightened the bent spring that is inside and manage to collimate that so it was almost bang on straight. I did the same with the laser as I did the Cheshire and forced it to look upwards via the two grub screws and that was bang on without me touch anything. Right in the centre of the primary and back into the laser. So that looks promising. I didn't try moving the scope to different extremes as I forgot at the time. 

Not sure if it will work or not but I'll have look when it's clear. I haven't spoken to the supplier yet. If it doesn't work this time I might just get a replacement and see how that goes. I might get lucky with the next one.

This is how things look at the minute. It's hard to photograph down the Cheshire.

Edited July 22, 2020 by Jamgood

[alacant]

1 hour ago, Jamgood said:

I get this part to a near perfect circle

That's fine. Ignore the flat bit. It's probably where the aluminising has failed. Or the bevel hadn't been done properly.

This is now where you need the Cheshire sight tube with cross hairs.

Point the telescope at the sky or a bright surface with the 45° surface of the sight tube orientated so it is eveny illuminated. Take a shot through it with your 'phone and post it here.

Or get someone to do it for you.

You're very close now...

Cheers.

 

[Pixies]

I notice how you can't see the outer edge of the primary any more?

[Jamgood]

20 minutes ago, Pixies said:

I notice how you can't see the outer edge of the primary any more?

I could with the collimator cap but not with the Cheshire. The photo below is how it looked before I adjusted the primary slightly. Is it because of the focuser tilt, maybe?

Edited July 22, 2020 by Jamgood

[Jamgood]

28 minutes ago, alacant said:

Point the telescope at the sky or a bright surface with the 45° surface of the sight tube orientated so it is eveny illuminated. Take a shot through it with your 'phone and post it here.

 

 

I'll point it at the sky tomorrow after work. The lights are crap in my house. Migraine proof for the wife.

[Pixies]

5 minutes ago, Jamgood said:

I could with the collimator cap but not with the Cheshire. The photo below is how it looked before I adjusted the primary slightly. Is it because of the focuser tilt, maybe?

How big is the Cheshire?

 

[Jamgood]

6 minutes ago, Pixies said:

How big is the Cheshire?

 

Huge. Sticks out of the focus about 6" - I expected to be able to slide it in to the focuser but I don't have a correct fitting.

[Jamgood]

@PixiesLike I said earlier. Practically useless. 

[Pixies]

I've got a shorty collimator. The problem with that I find, is that I'm so short-sighted I can't focus on the cross-hairs with my glasses on, or focus on the doughnut with my glasses off.

[Jamgood]

I got one from FLO. It doesn't say the size but I figured it would slot into one of my attachments better than it does. I might see if FLO will let me return it as it's pretty useless at that distance.

https://www.firstlightoptics.com/other-collimation-tools/astro-essentials-cheshire-collimating-eyepiece.html

[Pixies]

One thing to consider, regarding how the collimation changes if you move the scope. Make sure the spider vanes are tight. After I had replaced my secondary, I found collimation would change when I raised or lowered the scope. After tightening them up, that was fixed. 

[Jamgood]

30 minutes ago, Pixies said:

One thing to consider, regarding how the collimation changes if you move the scope. Make sure the spider vanes are tight. After I had replaced my secondary, I found collimation would change when I raised or lowered the scope. After tightening them up, that was fixed. 

I have checked them and they are tight. Measured them also and from what I can see they are equal.

[alacant]

5 hours ago, Jamgood said:

Sticks out of the focus about 6"

That's fine. You only need to be able to see the reflection of the primary centre spot and the crosshairs. You have already centered the secondary. The Cheshire will notw take you to the correct tilt and rotation.

A nice way to do the secondary adjustment is with your 'phone up against the viewing hole in the Cheshire. Make sure you have m4 bolts to be able to adjust the secondary. It's well nigh impossible with a hex-wrench.

You're close to the point where it will suddenly dawn upon you when something clicks and you finally reach the what-was-all-the-fuss-about category. Collimation then takes you 10 seconds instead of 10 hours!

HTH