Collimation Collywobbles

[Stu1smartcookie]

Hi all experienced people out there . 

I have a very weird situation in that i found the urge to test collimation on my Newt only to find that through a collimation cap everything seemed central , but , through a long cheshire tube only half of the primary was in view ! Even more wierd was when i put my well collimated laser in the focuser it showed that collimation was miles off when first using the collimation cap , and when i rectified the secondary and finally got the laser dot to disapear when i put the collimation cap back in only half the primary wa visible , however the cheshire at least had the primary in view although the cross hairs were way out to the right when looking through the focuser . The crazzy thing is , i was able to obtain focus , although ive not been able to do a star test due to the quite horrendous weather 

So to sum up ... what do i believe , the collimation cap or the long cheshire and laser ?

KR 

Stu

 

[Spile]

For the secondary mirror use and trust the Cheshire eyepiece and sight tube combination tool. Keep the cap for alignment of the primary. 

[NGC 1502]

As above-  sort out the secondary with the  Cheshire/sight tube first.   When you’re ok with the secondary use the collimation cap to sort the primary. Whilst you’re using the collimation cap check that all primary mirror clips are visible and equidistant within the view. Fine tune the primary with a slightly defocussed star at night using medium/high power.

Are you absolutely certain  your laser is collimated and does it fit the focuser without any slop?   It’s always possible to accurately and precisely decollimate your scope with an iffy laser….

Ed.

[Stu1smartcookie]

8 hours ago, NGC 1502 said:

Are you absolutely certain  your laser is collimated and does it fit the focuser without any slop?   It’s always possible to accurately and precisely decollimate your scope with an iffy laser….

Thanks for the advice guys ... I used the scope last night ( actually viewing from inside the house , in front of a radiator through the window ) and despite the rising heat from the radiator the moon was really sharp , also when it got darker many stars were visible ) but its now obvious i havent got it set right . 

As for the Laser , i use a twist EP holder to make sure the laser or the cheshire is firm and central . 

Despite all of that i am going to follow the advice from above and use the cheshire first and then the collimation cap for the primary . 

Many thanks to both of you for your help . 

I'm normally ok with collimation ... Not sure whats happened this time . Lets just call it age related 😂

 

Stu 

[bosun21]

I always set my secondary mirror with a concenter(concentre) to the purists out there. This makes sure it's correctly centered in the focuser tube and that the tilt is correct. The primary is then a piece of cake. Doing it this way allows my Hotech 2" laser, Cheshire sight tube and collimation cap to all agree. Once done I only need to check the primary before each session.

[Mr Spock]

39 minutes ago, bosun21 said:

I always set my secondary mirror with a concenter(concentre) to the purists out there. This makes sure it's correctly centered in the focuser tube and that the tilt is correct. The primary is then a piece of cake. Doing it this way allows my Hotech 2" laser, Cheshire sight tube and collimation cap to all agree. Once done I only need to check the primary before each session.

Exactly what I do with mine. The secondary position is adjusted with a concentre, then the secondary and primary collimation with a laser with the primary checked at the start of each session - takes seconds 

[Kon]

I am not sure which scope you have but with my 200P the focuser was the issue. It has a lot of wobble. When I was collimating it, I found that all looked great with the cheshire but a star test was a bit off. Putting the cheshire back in it was off. I found as I was rotating the cheshire along the focuser it was wobbling even if I thought I had tighten it, or the tightening was never even. That of course throws your secondary being off, although it may not be the case. I resolved it by doing the collimation and making sure when I inserted eyepieces to be tighten the same way. The way the focuser is hold in place by the two thumb screws is also goining a lot of play. Not an issue for visual but for planetary imaging I wanted to have it spot on. This way star tests looked perfect.  Life is too sort for this kind of thing so I recently moved to a low profile focuser as it is a lot more steadier and with the use of Baader clicklock I get even tightening. I have eleiminatedthe wobble of the focuser and it has made collimation a walk in the park.

[Rob]

I tend to use my Cheshire with a 2" to 1.25" twist lock adapter for both. I also check half way through a session as the scope moves from side to side (mostly double check when observing planets). The focuser colimation is important, and that's a rainy day check from time to time.

Rob

[Stu1smartcookie]

Thanks to all the above for the advice .

[Stu1smartcookie]

Just an update to my initial post . Last night i followed the advice and managed what seems like a spot on collimation . Of course no way of actually testing it due to the weather but it all looks back to normal . I really dont know why i messed around in the first place !!!! 

Thanks again 

[PeterStudz]

1 hour ago, Stu1smartcookie said:

I really dont know why i messed around in the first place !!!! 

Thanks again 

Fiddling with collimation when it isn’t necessary and making it worse is something that I’m sure everyone with a Newtonian has done at some point. I certainly have. And it’s often a sign that the weather is cloudy.

Sometimes you get complete beginners launching into it, getting in a mess, then coming on here when it really wasn’t necessary… first just get your new toy out under the stars. Before trying to fix a problem that might not exist!

[PeterStudz]

On 23/01/2024 at 11:20, Kon said:

I am not sure which scope you have but with my 200P the focuser was the issue. It has a lot of wobble. When I was collimating it, I found that all looked great with the cheshire but a star test was a bit off. Putting the cheshire back in it was off. I found as I was rotating the cheshire along the focuser it was wobbling even if I thought I had tighten it, or the tightening was never even. That of course throws your secondary being off, although it may not be the case. I resolved it by doing the collimation and making sure when I inserted eyepieces to be tighten the same way. The way the focuser is hold in place by the two thumb screws is also goining a lot of play. Not an issue for visual but for planetary imaging I wanted to have it spot on. This way star tests looked perfect.  Life is too sort for this kind of thing so I recently moved to a low profile focuser as it is a lot more steadier and with the use of Baader clicklock I get even tightening. I have eleiminatedthe wobble of the focuser and it has made collimation a walk in the park.

Interesting. I haven’t found this with the focuser on my 200p. However, I have taken it completely to bits and put it back together. I have also installed a Lacerta fine focuser, so it’s not quite the same as it was. It’s all rock solid. 

The only play that I noticed was in the stock extension tube for 1.25 eyepieces. I replaced that with something more substantial and of a different length. I did that because I didn’t like the amount of draw-tube that extended into the light path. Probably makes no visual difference but it annoyed me! So much so that I thought of taking a hacksaw to the end of the draw-tube. But a different extension tube sorted that too.

Edited January 24 by PeterStudz