Crosshairs AFTER laser collimation / NEWTONIAN 150/750

[JonKennedy]

Please help!

I have a NEWTONIAN 150 / 750 SKYWATCHER

I am seeing crosshairs and a dot even after LASER COLLIMATION!

When i look down the focuser empty I can see that secondary is potentially not PERFECTLY aligned, with a slight "moon crecsent" bottom right but upon mounting the laser all spots and targets line up perfectly!

I am at my wits end... PLEASE HELP!!

What am I doing wrong?

[johnfosteruk]

Is your laser collimator collimated correctly itself? 

 

[Peter Drew]

Seeing the "crosshair and dot" is nothing to do with collimation but everything to do with focusing. The crosshair and dot are the secondary mirror support vanes and the secondary mirror which show up when the telescope is out of focus.  

[johnfosteruk]

1 minute ago, Peter Drew said:

nothing to do with collimation

That shows I'm not paying attention, but hey ho it's late and you should collimate your collimator.

[REG78]

If you can get a chesire that will sort ur secondary out with a bit of tinkering should get everything centred Wat u wer on about lookn through without EP in try using ur lazer after that providing ur primary is centred hth

[spaceboy]

I think the problem most beginners to Newtonians face is they are terrified of messing with their scope in case they make a mistake. Laser collimators seem to install some sense of self confidence that as long as you get that red dot returning to the collimator all will be perfect.

I say all this as I was once there myself. For months I was happy the laser collimator was taking the worry out of the whole black art of collimation and I was getting the best views from my scope. Then one day I was sat bored at the PC and read this http://www.astro-baby.com/collimation/astro babys collimation guide.htm A collimation cap seemed easy enough to make out of an old focuser cap so out came the drill and 5 minutes later I'm looking down the draw tube to a secondary that was clearly not central. I though what the heck I'll get a Cheshire collimator as a back up as it didn't need batteries and at the same time I could check the collimation that the laser collimator said was spot on.

Needless to say cutting a long story short, collimation was way out and I now stick to a trusty Cheshire and collimation cap to do the job now. I barlow the laser collimator to take the stress out of collimation in the dark but other than that I don't recommend them, not for how easy collimation actually is. I agree it is easy to say collimation is easy now, but I can understand why so many panic especially if they are not confident messing with things. 

[David Levi]

Spaceboy is spot on. I bought my first ever telescope in August this year. It's a Sky-Watcher Explorer 200P. I used it for a month before I noticed a slight deterioration in image quality. Afraid of messing about and possibly messing up the scope I sought out what I thought was the easiest way to collimate the mirrors - a laser collimator. I bought a cheap laser collimator, about £20, and set about the laser collimation process. Straight away I realised that if I turned the laser in the focuser tube the red dot would move about on the primary mirror. This meant that the collimation process could never be accurate using the laser collimator in it's current condition. You need to collimate the laser collimator before using it so that the red dot does not move when you rotate the laser in the focuser tube. Anyway to cut to the chase, rather than faffing about collimating the laser I made a collimation cap out of an old 35mm film canister and bought a Cheshire collimator. One thing I would add to the brilliant explanation of collimation by astrobaby is that, in my telescope at least, you have to have the collimation cap as far as it will go into the focuser (i.e. flush with the top of the focuser tube) in order to see the primary mirror clamps. I probably spent a couple of hours familiarising myself with the collimation process the first time I did it but now spend 5 minutes to check or slightly adjust the primary mirror.

[wookie1965]

I used Astrobaby`s and this do do mine, http://www.schlatter.org/Dad/Astronomy/collimate.htm

when I first tried took me two days to do it. Now I have stripped my 200p flocked it put it all back together collimated it in around 40 mins. I had a laser collimator could not collimate it, it was always out so threw it in the bin got a Cheshire/Sight tube. Having said that i recently purchased another laser and a fellow sgler and friiend LeeB has collimated for me I will be picking it up at SGL12.

[Davesellars]

The best thing you can do is buy the Rigel Aline collimation cap or make your own.  I think the collimation cap is the best tool for ensuring that your secondary is centred and rounded under the focuser like the photos attached.  rack out the focuser until you've almost fillled the entire secondary - all must be equal around the reflection of the primary in the secondary.  If it is not equal then at some point as the focuser is drawn out light will fall outside of the secondary and be lost.

Once you've ensured the above you align the axis of the focuser to the primary either with your laser collimator or a Cheshire.  As people have mentioned your laser will need collimating to ensure it is accurate otherwise it is worthless as a tool.

Most likely if you're seeing a crescent the rotation of the vane is off this can happen easily by rough adjustment of the secondary tilt as the weight of the secondary mirror means that if two screws are sufficiently loose the vane will rotate around.  Avoid this by loosening only by a small amount at a time each tilt adjuster.

[JonKennedy]

15 hours ago, johnfosteruk said:

Is your laser collimator collimated correctly itself? 

 

I collimated the laser with a JIGG and paper on the wall.. 

[JonKennedy]

15 hours ago, Peter Drew said:

Seeing the "crosshair and dot" is nothing to do with collimation but everything to do with focusing. The crosshair and dot are the secondary mirror support vanes and the secondary mirror which show up when the telescope is out of focus.  

So this is a simple thing of using the FOCUSER ( up and down ) to see clearly.... can't be THAT simple and besides I have obviously tried this.

I am seeing something like this at full ZOOM depth when looking at a bright star . . 

[JonKennedy]

5 hours ago, Davesellars said:

The best thing you can do is buy the Rigel Aline collimation cap or make your own.  I think the collimation cap is the best tool for ensuring that your secondary is centred and rounded under the focuser like the photos attached.  rack out the focuser until you've almost fillled the entire secondary - all must be equal around the reflection of the primary in the secondary.  If it is not equal then at some point as the focuser is drawn out light will fall outside of the secondary and be lost.

Once you've ensured the above you align the axis of the focuser to the primary either with your laser collimator or a Cheshire.  As people have mentioned your laser will need collimating to ensure it is accurate otherwise it is worthless as a tool.

Most likely if you're seeing a crescent the rotation of the vane is off this can happen easily by rough adjustment of the secondary tilt as the weight of the secondary mirror means that if two screws are sufficiently loose the vane will rotate around.  Avoid this by loosening only by a small amount at a time each tilt adjuster.

PERFECT! It sounds like my laser is out... although i HAVE done the laser test with a JIGG by using the focuser itself and having the laser shoot past the secondary onto the wall and drawing a bit on a piece of paper!

[JonKennedy]

7 hours ago, spaceboy said:

I think the problem most beginners to Newtonians face is they are terrified of messing with their scope in case they make a mistake. Laser collimators seem to install some sense of self confidence that as long as you get that red dot returning to the collimator all will be perfect.

I say all this as I was once there myself. For months I was happy the laser collimator was taking the worry out of the whole black art of collimation and I was getting the best views from my scope. Then one day I was sat bored at the PC and read this http://www.astro-baby.com/collimation/astro babys collimation guide.htm A collimation cap seemed easy enough to make out of an old focuser cap so out came the drill and 5 minutes later I'm looking down the draw tube to a secondary that was clearly not central. I though what the heck I'll get a Cheshire collimator as a back up as it didn't need batteries and at the same time I could check the collimation that the laser collimator said was spot on.

Needless to say cutting a long story short, collimation was way out and I now stick to a trusty Cheshire and collimation cap to do the job now. I barlow the laser collimator to take the stress out of collimation in the dark but other than that I don't recommend them, not for how easy collimation actually is. I agree it is easy to say collimation is easy now, but I can understand why so many panic especially if they are not confident messing with things. 

A thought / problem I have is : when i put the laser collimator in ( which is perfectly collimated within itself ) there are 2 tightening screw's, now, i can potentially send the laser OFF CENTRE by tightening one screw more than the other... how do I avoid this? : /

[Davesellars]

23 minutes ago, JonKennedy said:

PERFECT! It sounds like my laser is out... although i HAVE done the laser test with a JIGG by using the focuser itself and having the laser shoot past the secondary onto the wall and drawing a bit on a piece of paper!

I don't think there's any real way of using the laser for ensuring the position of the secondary is correct under the focuser.  Use the collimation cap - with this you can ensure you're getting 100% illumination.  After this step you're aligning the axis of the focuser to the primary via the secondary using the 3 tilt screws (or knobs...) using the laser or cheshire tool.

15 minutes ago, JonKennedy said:

A thought / problem I have is : when i put the laser collimator in ( which is perfectly collimated within itself ) there are 2 tightening screw's, now, i can potentially send the laser OFF CENTRE by tightening one screw more than the other... how do I avoid this? : /

Yes, this obviously will be an issue.  Can be rectified somewhat by using a 2" to 1.25" adapter with a compression ring but even then it may be out.  To be 100% certain you need to use a self centering 2" to 1.25" adapter.

 

[JonKennedy]

6 minutes ago, Davesellars said:

I don't think there's any real way of using the laser for ensuring the position of the secondary is correct under the focuser.  Use the collimation cap - with this you can ensure you're getting 100% illumination.  After this step you're aligning the axis of the focuser to the primary via the secondary using the 3 tilt screws (or knobs...) using the laser or cheshire tool.

Yes, this obviously will be an issue.  Can be rectified somewhat by using a 2" to 1.25" adapter with a compression ring but even then it may be out.  To be 100% certain you need to use a self centering 2" to 1.25" adapter.

 

OK! I'll try a mixture of Cheshire and laser!
My worry is if and when I take this into the countryside I have to do this all at night, in a field, with a torch!

[Davesellars]

There's no problem using the laser (as long as the laser is collimated).  Once your secondary is setup it should not shift hardly ever so in the field once setup just check the primary using the laser.  I'd get it right with the tools you have at the moment but do a DIY collimation cap to check the position of the secondary or purchase the Rigel one from FLO.

[JonKennedy]

5 minutes ago, Davesellars said:

There's no problem using the laser (as long as the laser is collimated).  Once your secondary is setup it should not shift hardly ever so in the field once setup just check the primary using the laser.  I'd get it right with the tools you have at the moment but do a DIY collimation cap to check the position of the secondary or purchase the Rigel one from FLO.

If I am seeing something like this (BELOW PICTURE) am I about right?

I can focus on the roof of a building in the distance only 200metres from here perfectly but not on something further than 1km (on land) a tower for example with lights on, where the lights look like teh picture below also, with black dot in teh middle

[CraigT82]

4 minutes ago, JonKennedy said:

If I am seeing something like this (BELOW PICTURE) am I about right?

I can focus on the roof of a building in the distance only 200metres from here perfectly but not on something further than 1km (on land) a tower for example with lights on, where the lights look like teh picture below also, with black dot in teh middle

You're just not reaching focus, that's all, nothing to do with your collimation!

Are you using just the 1.25" adapter in the focuser and not both that and the 2" adapter, this is a common error (using them both that is)

[Davesellars]

I noticed from your picture of your setup that you have the 2" extension in as well as the 2" to 1.25" adapter/extension a the same time?  You should be only using one of these in the focuser otherwise you're going to have an issue reaching focus at infinity.  That would probably explain that issue.

Your other issue as you explained in your original post was about when you looked through the focuser and saw a crescent (so not completely illuminated).  Probably best to take another look and take a photo of this (like my photos that I attached to my first post...)

[wookie1965]

Star test with high power and turn focuser one way then the other should get airy disc with concentric rings, and collimating in dark is easy shine red light on shiny surface of the Cheshire its very easy.

[JonKennedy]

31 minutes ago, CraigT82 said:

You're just not reaching focus, that's all, nothing to do with your collimation!

Are you using just the 1.25" adapter in the focuser and not both that and the 2" adapter, this is a common error (using them both that is)

Oh my... i had BOTH adaptors in!

Will this fix my crosshair problem when looking at stars now?

[Astro Imp]

38 minutes ago, JonKennedy said:

Oh my... i had BOTH adaptors in!

Will this fix my crosshair problem when looking at stars now?

You should be fine now. It baffles me why there is nothing in the manuals about only using one adaptor, this is such a common problem that newcomers encounter.

Good luck and keep us informed.

[spaceboy]

2 hours ago, JonKennedy said:

A thought / problem I have is : when i put the laser collimator in ( which is perfectly collimated within itself ) there are 2 tightening screw's, now, i can potentially send the laser OFF CENTRE by tightening one screw more than the other... how do I avoid this? : /

The only way is http://www.telescopehouse.com/revelation-self-center-adapter-1-25.html but in all fairness your eyepieces are going to be held with the same screw configuration so if your Cheshire is lined up showing good collimation the so should your eyepieces.

[JonKennedy]

17 hours ago, Davesellars said:

I noticed from your picture of your setup that you have the 2" extension in as well as the 2" to 1.25" adapter/extension a the same time?  You should be only using one of these in the focuser otherwise you're going to have an issue reaching focus at infinity.  That would probably explain that issue.

Your other issue as you explained in your original post was about when you looked through the focuser and saw a crescent (so not completely illuminated).  Probably best to take another look and take a photo of this (like my photos that I attached to my first post...)

wow... such a simple and small mistake that no one ever noticed to asked me about until I came on here!

ThanK you so much!!!

[JonKennedy]

17 hours ago, Astro Imp said:

You should be fine now. It baffles me why there is nothing in the manuals about only using one adaptor, this is such a common problem that newcomers encounter.

Good luck and keep us informed.

You are absolutely correct!

I am quite a sharp, bright, mathematical chap and I can promise anyone starting they will NOT find this info at a basic level. I had to search the web and eliminate errors just to get to the point where I was reaching out to smart and experienced folks like yourself!

I really appreciate this!

JK