Sky-Watcher 200p classic collimation issues

[JD Astro Novice]

Hi guys, apologies in advance if I was supposed to just post this on an existing thread I’ve only just joined today. I can appreciate this is a really common topic that’s probably been discussed a lot and I have read up on here a bit but I’m still at a loss with a few things. 
 

I personally chose to go with a Cheshire eye piece to collimate as most forums and YT videos mentioned these can also be out of collimation. When I set up my telescope, at first glance it appeared to be okay in terms of what “good” looks like e.g. 3 primary clips, centred secondary mirror (black) and then the eyepiece reflection with the cross hair inside the circular doughnut. 
 

However, from looking at the secondary mirror in the eyepiece this is not a perfect circle, it is somewhat of a tilted oval shape. Now, the instructions in the manual state this should be a circle, and so do the majority of images and instructions on YT. Therefore, I have done just about everything I know to get that mirror circular e.g centre screw adjustment, and the 3 small screw adjustments, rotating the mirror and attempt to tilt it but nothing in the view changes it. Only thing I haven’t done is check the length of the spider veins so that could be something? also when looking through the Cheshire should the cross hair be in line with the veins reflected in the primary mirror? 
 

any advice would be great guys, I don’t mind doing stuff like this but without anyone there to show you I have no idea if what I’m looking at is fine as on a few videos I’ve seen the oval shape of the secondary mirror is viable so it could be fine. 
 

cheers 

[Spile]

Ignore the reflectionx2 of the spider vanes. Once you have run through the initial checks* (focuser and spider) then I would deal with the coarse adjustment. First confirm the offset so a=b and then the rotation. With the bolts loosened and the secondary in your palm you should be able to confirm that it’s possible to get the outline of the secondary circular and under the cross hairs. Next go through the fine adjustments.

The crosshairs of the sight tube should intersect with the centre mark and the dark offset secondary reflection (x2) should be offset toward the primary mirror.

If the checks above are done and the secondary is still slightly oval, I’d ignore it.

*I go through the process here https://astro.catshill.com/collimation-guide/

Edited December 28, 2022 by Spile

[Ricochet]

The centre screw is for moving the secondary up and down the tube so that you can have it directly under the focuser. All other adjustments are via the three collimation screws. These are the ones you need to adjust. You may find it easier to back all three off, use your hand to hold the secondary stalk, manually turn/angle it to the correct position and then tighten the collimation screws. This is not the easiest thing as you need to be looking down the Cheshire with two hands down the front of the scope. 

[JD Astro Novice]

Thanks Both, appreciate the extra info. I have to admit Spile those steps in the link you sent me aren’t really written in a way for a complete novice like me and loads of other guidance just differs so much. I really need a lehmans description as I sort of get lost when you ref a=b and an offset to x etc. I understand the components and the parts and the purposes. 
 

I managed to get a slightly less shaped oval but still can’t get a perfect circle no matter how much I adjust. I’ve followed the initial steps and the veins are all equal. I haven’t loosened the centre screw and only adjusted with the 3 small screws. This still only results in an off centre alignment with the secondary mirror through the Cheshire. Even with this and then alignment of the primary I managed to get a pretty perfect view of the moon tonight with great detail so is it really out of collimation? I then get thrown when looking at a bright object like Mars and when I focus right out it is clearly not aligned with quarter of the primary out of shot. 
 

it’s odd that I don’t see many people on here struggling with the secondary shape but I’m assuming it’s what is causing me all the grief. I think I may need to completely reset and tighten everything and then start again?
 

oh and the secondary is under the focusser so that seems to be all good. Any lehmans steps you’d advise me to do would be great from like a reset position. Unfortunately this is all so new to me so you’ll have to bear with me. 
 

 

[Ricochet]

9 hours ago, JD Astro Novice said:

This still only results in an off centre alignment with the secondary mirror through the Cheshire

Can you explain further what you mean by this comment? In what way is it off centre? If the telescope tube is horizontal with the open end at the left, in which way is the secondary(?) offest? Also, if you can get a photo through your cheshire and upload it here it would help us to advise what you need to do.

9 hours ago, JD Astro Novice said:

Even with this and then alignment of the primary I managed to get a pretty perfect view of the moon tonight with great detail so is it really out of collimation?

It might be out, without photos I can't really say, but as you have found, collimation doesn't have to be perfect which is good news as it means that you don't have to worry about it too much. Sure, to squeeze every last drop of performance out of the scope it needs to be good but if you have the choice between tearing your hair out for 99.9% performance and not worrying about it and getting 90% go with the later. No one got a spot on collimation the first time they tried it and each time you give it another go you'll get slightly better at it. In the meantime just enjoy using the telescope.

9 hours ago, JD Astro Novice said:

I then get thrown when looking at a bright object like Mars and when I focus right out it is clearly not aligned with quarter of the primary out of shot. 

Is Mars centred in the field of view when you do this? If it is could you roughly draw what it is that you see?

10 hours ago, JD Astro Novice said:

I think I may need to completely reset and tighten everything and then start again?

Not completely. You've said your spider vanes are equal lengths so don't touch those. The steps you want to use are:

1. Adjust centre screw (and also loosen/tighten collimation screws to match) to get secondary centred under focuser. If you've got your scope horizontal this means you want the same space between the edge of the secondary mirror and the wall of your cheshire to both the left and right.
2. Adjust the collimation screws to get the mirror appearing to be circular. As above. you may find it easier to back of the collimation screws so you can use your hand to hold the mirror in the correct position and then tighten them up. You may also need to use these to move the mirror up/down when viewed through the cheshire. 
3. Adjust the three collimation screws so that the cheshire crosshair points at the doughnut in the centre of the primary. If this messes up step 2, don't worry about it and move on.
4. Adjust the primary mirror so that the black dot created by the peep hole in the centre of the cheshire is centred in the doughnut on the primary mirror.

[JD Astro Novice]

Thanks Ricochet, this is super helpful! 
 

So I think I have cracked it which was down to making a collination cap and not relying on just the long Cheshire. In addition I used the 2 pieces of coloured card method and this helped me see whether the secondary mirror was circular or not. Oddly when I removed the cards it was then a circle from the adjustments with the small screws. I’m not sure why my eyes couldn’t see this as a circle previously but atleast were there I think. 
 

Also in the Cheshire it does show all primary clips whereas the cap does so I think that’s what threw me also. I’ve attached a pic of the Cheshire view and then the cap, let me know if that’s what I should be seeing as you mentioned I have been pulling my hair out for about 4 days doing this l 😂. 
 

[Ricochet]

41 minutes ago, JD Astro Novice said:

let me know if that’s what I should be seeing

If you adjust the focuser to move the Cheshire out a bit it might show the other clips and then maybe a bigger gap on the left (so the secondary should move up the tube by shortening the centre screw). I can't make out exactly where the edge of the Cheshire is though to be sure. 

However, I think for a first time collimation that is a cracking effort and you should congratulate yourself for a job well done and get out under the stars and enjoy using the scope. 

[Spile]

Visually it looks fine and I personally would not change the secondary any more. As for the guide, what ever makes sense to you. I read a number of them before I wrote something that made sense to me.

In its simplest sense for the secondary, the question I ask is, can I see all of it and is it centred under the focuser. 
Aka…

[Spile]

Spot on...

 

[Spile]

A sheet of coloured paper behind the focus tube would make it easier to identify the edge of the secondary...

Edited December 31, 2022 by Spile

[JD Astro Novice]

On 31/12/2022 at 10:33, Spile said:

A sheet of coloured paper behind the focus tube would make it easier to identify the edge of the secondary...

 

On 31/12/2022 at 10:29, Spile said:

Spot on...

 

Thank you for this, given me a lot of peace of mind. Where I had to play with this quite a bit when first setting up it hasn’t given me a lot of confidence that I have an accurate set up for observing. 
 

feels like a bit of relief getting your analysis above on the collimation and nod that it’s correct. I feel like it’s clicked for me now, the sheets of paper helped do that and the collocation cap. I think I assumed just using a long Cheshire site tube would just do it all for me and it really didn’t. Great for the final part e.g. alignment of primary with secondary etc. but the set up of the secondary is the hardest part. 
 

what I did find though was I couldn’t fully tighten one of the fine adjustment screws without moving the secondary, so I’ve left only one slightly slack as I’m conscious I’ll mess up what I’ve done.

[tooth_dr]

On 31/12/2022 at 10:33, Spile said:

A sheet of coloured paper behind the focus tube would make it easier to identify the edge of the secondary...

Just don’t do what I did and forget the paper was there, then wonder why my stars were weird when i went to use the scope (the paper had fallen down and was obscuring 75% of the primary mirror!)

Edited January 6, 2023 by tooth_dr

[JD Astro Novice]

Can I also ask should the reflection through the Cheshire be slightly offset towards the focus tube? In order to get the both circles concentric and centred? When you look at my picture the inner most circle is centre however in order to achieve this 2 of the adjustment screws are loosened. If I tighten both then it forces the inner circle to move offset towards the focusser. Almost indicating it should be offset. 
 

reading the Astro baby guidance it says for fast Newtonians like mine the skywatcher classic 200p it should be offset not directly centred. Any advice would be great as obviously when moving it around will knock the collination out for secondary without the screws tightened. 
 

unless of course I need to perhaps tighten the centre screw down more then tighten the smaller screws. Or the other way around. 

[Spile]

8 hours ago, JD Astro Novice said:

what I did find though was I couldn’t fully tighten one of the fine adjustment screws without moving the secondary, so I’ve left only one slightly slack as I’m conscious I’ll mess up what I’ve done.

By very very slightly altering the other bolts and working your way round you get all three secure.

[Spile]

7 hours ago, JD Astro Novice said:

Can I also ask should the reflection through the Cheshire be slightly offset towards the focus tube? In order to get the both circles concentric and centred? When you look at my picture the inner most circle is centre however in order to achieve this 2 of the adjustment screws are loosened. If I tighten both then it forces the inner circle to move offset towards the focusser. Almost indicating it should be offset. 
 

reading the Astro baby guidance it says for fast Newtonians like mine the skywatcher classic 200p it should be offset not directly centred. Any advice would be great as obviously when moving it around will knock the collination out for secondary without the screws tightened. 
 

unless of course I need to perhaps tighten the centre screw down more then tighten the smaller screws. Or the other way around. 

Refer to the labelled diagram above, the dark reflection of the secondary should be offset in the direction of the primary and as my guide says, this is a useful check. 

 

As for the central screw, if a=b and there is no rotation error, tighten it if it’s slack but the push-pull arrangement means that it shouldn’t be. So just work through the three outer bolt’s sequentially and very gradually.

[JD Astro Novice]

1 hour ago, Spile said:

Refer to the labelled diagram above, the dark reflection of the secondary should be offset in the direction of the primary and as my guide says, this is a useful check. 

 

As for the central screw, if a=b and there is no rotation error, tighten it if it’s slack but the push-pull arrangement means that it shouldn’t be. So just work through the three outer bolt’s sequentially and very gradually.

Ah so It’s collimated correctly in that case then. It  naturally wants to be offset towards the primary mirror when I tighten both screws gradually. It’s confusing as the user manual states everything must be centred and concentric. I really feel for people who didn’t have guidance like this back in the day.

even makes me wonder how on earth Issac Newton collimated this 😂

just to clarify what are you referring about to as a & b in that example? 

[Spile]

23 hours ago, JD Astro Novice said:

It’s confusing as the user manual states everything must be centred and concentric. I really feel for people who didn’t have guidance like this back in the day.

 

just to clarify what are you referring about to as a & b in that

The manual should say everything apart from the offset secondary reflection.

a b c d e f are what I use in my guide above to identify the distances  important for collimation.

[bosun21]

On 06/01/2023 at 14:25, JD Astro Novice said:

 

reading the Astro baby guidance it says for fast Newtonians like mine the skywatcher classic 200p it should be offset not directly centred.

When I collimate my Stella Lyra 8” (200mm) f6 which is the same as your skywatchers optical design the reflection of your cap or Cheshire should be offset towards the open end of your scope. This differs for different telescopes f ratios. At first I wasn’t adept enough at collimation to achieve this every time so used it the way yours is. Practice makes perfect and before long you will wonder what all the fuss was about. I now never need to touch my secondary mirror and only tweak the primary with a HoTech laser before every session. 

[Ricochet]

10 hours ago, bosun21 said:

the reflection of your cap or Cheshire should be offset towards the open end of your scope

It may appear that the cap reflection is offset away from the primary but in fact it is the shadow of the secondary which will appear offset towards the primary mirror. The reflection of the cap and the central hole should be perfectly centred, with the hole appearing as a dot inside the also centred primary doughnut.

This image from @Spile's guide shows it best. The central dark spot, light circle and red/green/blue circles are all concentric and the dark dot sits exactly under the centre point marked by the cheshire crosshairs. Only the larger dark circle (secondary shadow) is offset from the centre.

Edited January 8, 2023 by Ricochet

[bosun21]

1 hour ago, Ricochet said:

It may appear that the cap reflection is offset away from the primary but in fact it is the shadow of the secondary which will appear offset towards the primary mirror. The reflection of the cap and the central hole should be perfectly centred, with the hole appearing as a dot inside the also centred primary doughnut.

This image from @Spile's guide shows it best. The central dark spot, light circle and red/green/blue circles are all concentric and the dark dot sits exactly under the centre point marked by the cheshire crosshairs. Only the larger dark circle (secondary shadow) is offset from the centre.

I always took the red ring to be the secondary mirror that’s why it’s centered in the focuser tube. and can show the reflection of the primary mirror. And the central dark area is a reflection of the cap or the poorly reflective surface of the cap/Cheshire. If I’m wrong please explain to me how you get a secondary shadow please. Or is it the shadow of the secondary as seen by the primary mirror?

Edited January 8, 2023 by bosun21
Typo

[Ricochet]

16 minutes ago, bosun21 said:

I always took the red ring to be the secondary mirror that’s why it’s centered in the focuser tube. and can show the reflection of the primary mirror. And the central dark area is a reflection of the cap or the poorly reflective surface of the cap/Cheshire. If I’m wrong please explain to me how you get a secondary shadow please.

When you collimate the telescope you do so with the front cap off. Light comes into the telescope, reflects off the primary and secondary and into your eye. This is why the primary appears to be bright - the large white area in the image. In the centre of the opening at the top of the telescope you have the secondary mirror and spider which blocks the light entering the tube. This is why there is a large dark area in the centre with four dark spider vanes shown horizontally and vertically. The reflection of the cap is the small bright area in the centre. Inside this you will see the dark central spot which is the hole in the cap (where there is no reflective material) and also a dark deflection of the primary doughnut.

Here is a photo taken through a collimation cap. It is too dark around the outside to see the edge of the secondary mirror so everything you are seeing is reflections. Working from outside in you have:

1. Bright reflection of primary with three shadows of mirror clips. If you look carefully at the left hand side you can see if goes slightly flat where the focuser drawtube just grazes the light path.
2. Dark shadow of the secondary mirror with four spider vanes. You can note that the horizontal spider vanes are not quite parallel and you can see screw heads protruding from the spider on the left, bottom and top (just!) sides. You may also notice that this shadow is not actually round because the central boss of the spider is large and the mirror is offset so there is a crescent of shadow to the left that is the central boss not the secondary mirror itself. In a different brand telescope with a smaller boss you would see only the shadow of the secondary and the shadow should be round (but offset).
3. Bright central area. This is the reflection from the reflective surface on the underside of the collimation cap
4. Dark ring. This is the reflection of the doughnut in the centre of the primary.
5. Dark dot. This is the shadow of the hole in the centre of the collimation cap.

 

[Spile]

10 hours ago, bosun21 said:

I always took the red ring to be the secondary mirror that’s why it’s centered in the focuser tube. and can show the reflection of the primary mirror. And the central dark area is a reflection of the cap or the poorly reflective surface of the cap/Cheshire. If I’m wrong please explain to me how you get a secondary shadow please. Or is it the shadow of the secondary as seen by the primary mirror?

The red ring is the edge of primary reflection. The green ring is the actual edge of the secondary. The offset secondary reflection (rx3) is dark because it’s the bottom edge of the sight tube. I’ve broken each reflection down here https://astro.catshill.com/through-the-eyepiece-tube/

[bosun21]

21 hours ago, Spile said:

The red ring is the edge of primary reflection. The green ring is the actual edge of the secondary. The offset secondary reflection (rx3) is dark because it’s the bottom edge of the sight tube. I’ve broken each reflection down here https://astro.catshill.com/through-the-eyepiece-tube/

I wholeheartedly understand the art of collimation and actually meant the green ring as the red is the reflection of the primary mirror. I know  what everything should look like. It’s the offset of the reflection of the collimation cap I was wrestling with. Every other diagram I’ve seen the offset is towards the open end of the tube like mine is. Yours shows the offset towards the focuser tube? I have done numerous tracked star tests and on Polaris and they are virtually perfect. The mystery continues. Thanks 

Edited January 9, 2023 by bosun21
Typo

[Spile]

2 hours ago, bosun21 said:

I wholeheartedly understand the art of collimation and actually meant the green ring as the red is the reflection of the primary mirror. I know  what everything should look like. It’s the offset of the reflection of the collimation cap I was wrestling with. Every other diagram I’ve seen the offset is towards the open end of the tube like mine is. Yours shows the offset towards the focuser tube? I have done numerous tracked star tests and on Polaris and they are virtually perfect. The mystery continues. Thanks 

First of apologies for any misunderstanding. I am confused because the only thing I have offset in my diagram is the dark reflection of the secondary and that  “points” away from the focus tube towards the primary mirror. The bright ring of the cap isn’t offset.

[bosun21]

1 hour ago, Spile said:

First of apologies for any misunderstanding. I am confused because the only thing I have offset in my diagram is the dark reflection of the secondary and that  “points” away from the focus tube towards the primary mirror. The bright ring of the cap isn’t offset.

I agree, The only the thing that appears offset is the dark reflection of the secondary holder, but for some reason to your eyes it appears that it’s the bright reflection of the cap/donut that is offset. But that’s obviously not the case as verified by the Cheshire crosshairs being perfectly centered with my donut. Thanks for taking the time to explain this in a more detailed manner. ATB  

     Ian