Collimation way off

[Ben2121]

Hello, I recently purchased a Celestron Omni 150. I tried looking at the moon but couldn't focus the image with a 25mm. I then used a laser collimator to try and fix the issue, since it seemed that it was off (laser not in center of secondary mirror). The laser is way off to the corner - I tried adjusting the 3 screws, loosening and tightening, but I can't seem to get the laser near the middle. Is there any shortcut to get it pointed near the middle and then adjust? Is there any other step that I am missing? Thanks.

[Alan64]

I have an Orion(of California) 150/750 Newtonian...

Yours is a bit more deluxe than my basic model.  Both are manufactured by Synta, perhaps in the same factory overseas even. 

I can't help but to suggest to set aside the laser-collimator, as the entry-level types oft require collimating themselves, and before using to collimate a telescope. 

I use the passive tools instead, tried and true.  I use a sight-tube, and a collimation-cap(as a second-opinion and fail-safe)...

When using said tools, the telescope, its interior, requires illuminating...

Bang on...

Afterwards, I see glory.

A combination Cheshire/sight-tube...

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

Collimation-cap...

https://www.firstlightoptics.com/other-collimation-tools/rigel-aline-collimation-cap.html

In the U.S....

https://agenaastro.com/agena-1-25-collimating-eyepiece-newtonian-reflectors.html

https://agenaastro.com/rigel-systems-aline-telescope-alignment-eyepiece.html

Collimation instructions/tutorials are widely available online, in text-form with images, and videos too.

Laser-collimators are preferred by users of larger Newtonians, "Dobsonians" 8" and up in particular.  You can certainly continue to use your own, but it should be checked for collimation, and adjusted if needed...

https://www.youtube.com/watch?v=5ZsgNlgIrqQ&t=98s

If you need more information, we'll be glad to help.  Just ask away.

Edited May 22, 2021 by Alan64

[Carbon Brush]

Excellent advice from Alan.

I have seen new scopes that need more than just the mirrors aligning.
Focus tubes that are not correctly aligned with or pointing to the secondary.
A secondary mirror that was way off the tube centre.
Primary mirrors looking more to the tube side than out of the end.

We all appreciate a scope is not going to be correctly collimated on arrival. But some should not have got out of the factory door.

As this is a new scope, take nothing for granted. Make sure the scope looks to be correctly assembled and mechanically set up before starting on optical issues.

For example, place the OTA level on the mount. Then walk away and keep looking down the tube.
Look for a main mirror reflection. As you walk away, can you still see 100% of the mirror? or is it like a gibbous moon? Do you start to see the outside of the OTA while keeping the mirror in view?
This indicates a gross primary misalignment.

Does the secondary mirror look to be correctly placed (glued) on the carrier in the spider, on the tube centre?

Find a piece of wood, plastic drain pipe or anything that is a good fit in the eyepiece holder.
Move the wood carefully towards the secondary mirror. It is central on the mirror?

Keep asking, everyone will be happy to help.

David.

 

[Spile]

9 minutes ago, Carbon Brush said:

I have seen new scopes that need more than just the mirrors aligning.

That is interesting. Both the secondary and primary of my Skywatcher 200P were well aligned and certainly to the degree of "pleasing views".
I've since  acquired a Cheshire Eyepiece/ sight tube  to make more precise alignment easier.

[PeterStudz]

The one I had with my Skywatcher 1145P was the primary clips (two out of three) being loose. Before I worked it out I’d collimate it but as soon as it was moved it would go out again. 

[BrendanC]

The best thing I ever did for collimation was to replace the horrible screws on the secondary with some decent thumb screws. I got these but they're currently out of stock (isn't everything?): https://www.amazon.co.uk/Set-Thumbscrews-Secondary-Mirror-Collimation/dp/B00UJUOXA4

You might have more luck at Bob's Knobs - see http://www.bobsknobs.com/

They're so very much easier to manipulate because you can move more than one at a time without worrying about Allen keys falling out or dropping onto the primary etc.

Then yes, as others have said, use a collimation cap and/or a Cheshire, not a laser.

And follow this guide: https://www.astro-baby.com/astrobaby/help/collimation-guide-newtonian-reflector/

Good luck. I hate collimating. Or, rather, I hated collimating until I also got a Concenter which helped sort out the secondary, and now I just have a quick check with the Cheshire to align the primary - about a minute, and I'm done. Very occasionally I'll check the secondary with the Concenter but it's always spot on. It was more money than I wanted to spend, but I'm glad I spent it. I also developed a solution using my mobile phone in case you'd like to give that a go, see https://stargazerslounge.com/topic/360299-interesting-collimation-technique/

Actually, come to think of it, I still hate collimating.

Edited May 21, 2021 by BrendanC

[Pitch Black Skies]

On 17/05/2021 at 23:49, Alan64 said:

Always collimate a telescope in a horizontal position...

I never do this, the reason being is that once my telescope is pointed vertically, I notice the primary mirror tilts back and sits flush in it's clips, and then collimation is off.

I always have it at around 45°. The clips should never be tight holding the primary mirror down. They are just designed to just prevent it from falling out, so they should have a little play.

As an experiment, collimate the telescope horizontally, then slew it vertically and see if collimation holds by testing with the collimation cap. If it does hold, inspect the primary mirror clips to ensure they are not clamping down the primary mirror resulting in pinched optics which is just as bad if not worse than poor collimation.

The only thing to be careful of with this method is the risk of dropping something down the tube!

 

Regards,

Alan

[Carbon Brush]

Most scopes, on arrival, will be OK.
@Spilecomment shows how we don't need to get too worked up about collimating every 5 minutes.👍

However in these days of mass produced scopes from China, they are drop shipped by retailers. They are therefore unchecked at the point of sale.
There will be some problems. The 'Christmas' scopes and those bought by anyone new to the hobby may not get the problems identified.

To the OP, if you have purchased from an astro retailer, go back and talk to them.
I was once in Rother Valley Optics shop when a new scope owner came in to ask about poor views through his scope.
From memory it was a 130 or 150 newt that would have been drop shipped.
The shop owner, Ian, asked a few questions to establish sky quality, eyepiece choice, cool down, etc.
I was thinking to myself 'collimation check' - just as Ian told the customer he thought that was the problem.
He told the customer to bring in the scope and he would sort the collimation.
The customer asked if there would be any charge? No. Can I watch to learn? Yes definitely.
Try that with PC World or Amazon😕

A couple of years back I was collecting a scope from an SGL member and we were chatting, as happens.
He talked about collimation issues with an 8" newt he owned. Having owned, dismantled and reassembled a few newts, I offered to look. Hoping that in 10 minutes I could give some pointers.
Normally a serious assembly or alignment problem in a newt can be quickly found with minimal tools/instruments then normal collimation can be started.
In this case 10 minutes working in his hall did not identify the issue - but it was obvious things were really off.

It is not always the mass market scopes that suffer. My first proper scope was an 8" newt from Orion Optics, built to order, bought 2003/4.
I could not collimate it and decided it was my lack of experience.
I went along to an astro club, who had the tools and the experience.
3 of their experienced members struggled, scratched their heads and finally declared "send it back". There was a focusser to secondary mirror alignment problem.
As it happens it went back for other reasons that meant the OTA was replaced.

Spending lots doesn't always help. There was a very active thread on SGL recently talking about pinched optics in Esprit fracs.

HTH, David.
 

 

[Captain Scarlet]

13 minutes ago, Pitch Black Skies said:

... The only thing to be careful of with this method is the risk of dropping something down the tube!

Regards,

Alan

Actually dropping something down the tube is likely not as bad as all that, unless the object is big or the tube is pointed very high. Obviously it's not something you want to do. Whenever I've dropped stuff down the tube, it's hit the tube-side and slid down to rest in the gap around the primary. It's been inconvenient, fishing it out again, or pointing the scope "down" to let it slide back out, but an allen key or some such is unlikely to hit the primary.

Also, I have a SW 200p solid-tube newt. I've had to bolster it with an air-conditioning ring-clip near the focuser to stiffen it up, because beforehand simply changing altitude would throw the collimation off.

M

Edited May 21, 2021 by Captain Magenta

[Pitch Black Skies]

4 minutes ago, Captain Magenta said:

Actually dropping something down the tube is likely not as bad as all that, unless the object is big or the tube is pointed very high. Obviously it's not something you want to do. Whenever I've dropped stuff down the tube, it's hit the tube-side and slid down to rest in the gap around the primary. It's been inconvenient, fishing it out again, or pointing the scope "down" to let it slide back out, but an allen key or some such is unlikely to hit the primary.

M

It's not mine, but was caused by an Allen key apparently. Always err on the side of caution..

[Captain Scarlet]

Oof. I reckon that was most likely caused by someone doing secondary mirror collimation/ placement with the tube resting on its bottom. I’d agree that’s an absolute no-no.

[Pitch Black Skies]

Quite possibly.

[Alan64]

9 hours ago, Pitch Black Skies said:

I never do this, the reason being is that once my telescope is pointed vertically, I notice the primary mirror tilts back and sits flush in it's clips, and then collimation is off.

I always have it at around 45°. The clips should never be tight holding the primary mirror down. They are just designed to just prevent it from falling out, so they should have a little play.

As an experiment, collimate the telescope horizontally, then slew it vertically and see if collimation holds by testing with the collimation cap. If it does hold, inspect the primary mirror clips to ensure they are not clamping down the primary mirror resulting in pinched optics which is just as bad if not worse than poor collimation.

The only thing to be careful of with this method is the risk of dropping something down the tube!

 

Regards,

Alan

Very well, then 45° it is.

Also, good point about the clips...

I try to shoot for a business- or index-card's thickness for my reflectors.

[Pitch Black Skies]

4 hours ago, Alan64 said:

Very well, then 45° it is.

Also, good point about the clips...

I try to shoot for a business- or index-card's thickness for my reflectors.

Looks perfect

[Alan64]

1 minute ago, Pitch Black Skies said:

Looks perfect

Now, those clips tend to hug the side of the mirror, but no pinching, I expect.

[Pitch Black Skies]

That's normal. Did you get a chance to point the scope vertical and inspect after collimating horizontal? It's possible you are unaffected, but for me it was a noticeable difference.

I noticed that the primary kept tilting forward at horizontal. I was unknowingly collimating in this position and as soon I pointed the scope up, all was lost. I only discovered this recently. I then made the silly mistake of clamping the primary down with the clips, until I discovered they should be at least a business card's width of a gap.

[wimvb]

The very first scope I bought (SW 150PDS) had issues on arrival. I attached the finder scope in its shoe, but no matter what I tried, I couldn’t get it aligned with the main scope. Even with a 25mm eyepiece, views through the scope were way off what I saw through the finder. I was about to return the 😖😡👿🤬 thing. Then I checked collimation ...

I used the end plug of a 32 mm drainage pipe as my first collimation cap. Just drilled a small hole in its centre. It fitted perfectly in a 1.25” eyepiece adapter. Collimation perhaps wasn’t spot on after that, but certainly a lot better than before.

Edited May 23, 2021 by wimvb

[Mr Spock]

With Newts it's always worth checking the collimation every time you go out. A laser collimator is the easiest for this and tweaking the primary mirror should take seconds.

The secondary, once set, shouldn't need touching. 

[Sabalias]

Hi All,

I'm interested to see mention of the mirror clips on this page. I recently flocked my 150 PDS. I also took the opportunity to clean off any loose dust and detritus from the primary mirror (just with a flow of water). I noticed that the screws holding the clips in place were extremely tight when I came to removing them and when I replaced them I didn't tighten them too much but, clearly, they need to be even looser. Why do you suppose the screws were so tight in the first place?

Stu

[Peter Drew]

It's my belief that manufacturers tighten the mirror clips to prevent the mirror from flopping about during transit from China to wherever.  One of the first things to check on the receipt of a new Newtonian.      🙂