Jump to content

Stargazers Lounge Uses Cookies

Like most websites, SGL uses cookies in order to deliver a secure, personalised service, to provide social media functions and to analyse our traffic. Continued use of SGL indicates your acceptance of our cookie policy.

Daveyboy

ok. so now im fed up !

Recommended Posts

hi all .

after spending most of the day cleaning my secondary mirror ive now fitted all the bits back together and im having a night mare trying to get it all collimated again , im starting to think something is a bit dodgy somewhere .

the first thing I noticed is when I attached the mirror back to the spider the base of the mirror mount doesn't sit flat onto the spider even with all the grub screws fully retracted .

then putting the spider back into the tube the fins seem  a little twisted even before they are tightend .

now im having issues lining up the secondary with the eyepiece , ive had it pretty much bang on centre but when I adjust the grub screws to line up the laser to the centre spot on the primary it throws it miles out again and I can only see half the primary through the secondary .

so I start lining up the primary with the laser and its a mile out through the eyepiece .

am I missing something here ???

better still , does anyone know to a place in the west mids where I could take the scope and get it sorted ?

 sorry to be a pain in the forum but its one big learning curve for me .

cheers and beers Dave

Share this post


Link to post
Share on other sites

Hi Dave.  Part of your problem may be that the 3 secondary adjuster screws have dug a pit into the secondary holder. When you turn one of the screws, it's rotating the secondary holder a bit.

Many have sorted that particular problem with a large washer between the ends of the 3 adjusters and the secondary holder.

Worked for me.  Hope you sort it, Ed.

  • Like 1

Share this post


Link to post
Share on other sites

The spider needs to be tensioned very evenly around the tube and quite firm before re-attaching the secondary. Do this a little at a time on opposite ends of each vein - just half a turn at a time ensuring you keep the secondary mounting dead central at all times.

The secondary should sit just off the spider - the collimation screws are meant to hold it totally free of it's mounting and the center screw holds it in place firmly up against the colli screws - but not too tight you can't collimate it. When replacing it ensure it's perfectly square on and in line with the focuser tube. When you look in the focuser tube it should appear perfectly circular.

If you get that bit right then the primary should be visible with all three mirror clips in view. If not then adjust the secondary angle and tilt as required. Once the three primary clips are in view then you should be able to get the laser on the primary center spot. Then you just need to tilt the primary so the beam reflects directly back up to the same spot.

If it doesn't reflect properly then you may not have reseated the primary properly. Or possibly tightened the mirror clips too much. They should hold the primary perfectly central in the cradle - but without pressure any where more than enough to keep it in place. It should ideally "cradle" the mirror so it doesn't move - rather than "grab" tight to hold in place.

It's a delicate operation but hope that helps. :)

Edit - Yup as above - there should be a washer between the secondary and the collimation screws - I too have forgotten to put the washer back in the past lol.

Edited by brantuk

Share this post


Link to post
Share on other sites

thanks for the replys guys ,

the mount on the secondary mirror does have some little dinks in where the grub screws have bitten into it , I thought I would be clever and turn the mount 180% so the grub screws don't line up with the existing marks anymore , this way I thought it would stop the need of a washer .

with this said I still cant seem to get it right . maybe im missing something or just way off .

 cheers Dave

Share this post


Link to post
Share on other sites

There are some Astronomy Shed videos on collimating newts that may be helpful, but I can't find the link at the moment.  It's in another collimation thread from this week.  If I find the link I'll post it here.

James

Share this post


Link to post
Share on other sites

Perhaps best to turn it back to the original position but as advised add a washer this time.  :smiley:

Share this post


Link to post
Share on other sites

This would be my worst nightmare, with a mechanical aptitude verging on nil I will stick to Refractors.

                                                                     mijijim

Share this post


Link to post
Share on other sites

   Perhaps these two links will help?

   http://legault.perso.sfr.fr/collim.html

   Or this one?

http://www.andysshotglass.com/Collimating.html

    In the future, after you sort the alignment out, when cleaning the secondary, use a soft tissue with isoprople ("rubbing") alcohol on it and reach the surface with your fingers and the wipe, then gently wipe the mirror. Any dust or lint that remains can be blown off.  Both mirrors can be pretty dirty before performance is effected.

  • Like 1

Share this post


Link to post
Share on other sites

Thanks for your help guys , muchly appreciated

I think I might have cracked it (not literally)

One thing I did notice wich may have been throwing me off was when I tighten the laser into the eyepiece it shows differently every time . What I mean is it all depends on how I tighten up the two holding screws in the eyepiece of the focuser , if I remove the laser and re insert it it will 9/10 show off the mark . I can adjust it by loosening the screws on the focuser and re tightening .

Is this a common problem or has anyone else encountered this happening with their laser ?

Cheers Dave

Share this post


Link to post
Share on other sites

I would not use a laser for the secondary at all since there are many combination possible of tilting  and rotating the mirror and you can use the 3 adjustment screws to show it is in line again, but that doesn't mean it is collimated right.

Also sounds the collimator is struggling with a bit of slop in the focuser and that is not helping you cause perhaps. Use a sight tube with the cross hairs is the best way to go IMHO.  Not that helps right now if that is the only tool you have got.

It may also be the case your laser is out of collimation. 

Have decent watch of the astronomy shed series with a brew, it is quite lengthy though, enough to have a couple or more brews  :smiley:

http://www.youtube.com/watch?v=8ROvNH5uwDo

Edited by AlexB67

Share this post


Link to post
Share on other sites

Ref the large washer, I believe some people have used a milk carton lid (you know the plastic ones) just trim the sides and there you have a cheap, replaceable sacrificial plate.

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.


  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.