Refractor collimation

[Moonshane]

19 hours ago, Stu said:

@Moonshane happy to send a Hotech 1.25" up to you to borrow so you can check it out. Any use?

Stu

What a kind offer mate. I might just see how it goes and if I can get it looking good without then I'll be happy. If it won't adjust out with the Cheshire then I'll almost certainly take you up on this 

[Moonshane]

Does anyone else think it's ironic that as a generally dob based observer (for night time anyway) I bought a frac that seems to need collimation!?

[John]

2 hours ago, Moonshane said:

Does anyone else think it's ironic that as a generally dob based observer (for night time anyway) I bought a frac that seems to need collimation!?

The thought crossed my mind but I've kept "mum" about it

Some of the fracs that I've owned needed tinkering with more than I expected as well

[spaceboy]

This is why I have always preferred refractors with collimateable cells like the blue tube sky watcher, Helios or Bresser refractors. 6 screws, screw driver /allen key and a chesire and you know your scopes performing at its best every time. Why they only did this with the achro's and not the ED range I have no idea ??? Shame they stopped the collimateable cells all together on the black diamond range but at least Bresser still offers it with their latest achro's and ed refractors.

[Stu]

3 hours ago, Moonshane said:

What a kind offer mate. I might just see how it goes and if I can get it looking good without then I'll be happy. If it won't adjust out with the Cheshire then I'll almost certainly take you up on this 

Just drop me a PM if you want to borrow it Shane, I think it might make aligning the focuser a much quicker job

[John]

1 hour ago, spaceboy said:

This is why I have always preferred refractors with collimateable cells like the blue tube sky watcher, Helios or Bresser refractors. 6 screws, screw driver /allen key and a chesire and you know your scopes performing at its best every time. Why they only did this with the achro's and not the ED range I have no idea ??? Shame they stopped the collimateable cells all together on the black diamond range but at least Bresser still offers it with their latest achro's and ed refractors.

My experience is that the Evostars and Meade / Bresser achromats have needed collimation adjustments whereas the ED's I've owned have not. Perhaps the mechanical tolerances on the former are a little more lax than the latter ?

 

[spaceboy]

Even so I'd prefer the ease of a collimateable cell over a fixed cell any day. OK refractors hold collimation well but they aren't bomb proof like some believe.

[Moonshane]

Not really made any progress with this other than discovring the poor quality of the collimation capacity. The steel grubs bear directly on the glass and despite not really exerting any major pressure on them, I have created a couple of small clamshell chips in the central element. Nice design! Stupidly, I assume there was some sort of plate between the grubs and the glass but alas no. I took it apart and now understand the whole thing a lot more although I don't think there's adequate adjustment room to get a good alignment. I think I'll just put up with mis-ollimation rather than create further damage.

[John]

Sorry to hear that Shane. Thats not a great design

I would have assumed that something would have been between the grub screw tip and the glass as well.

[Moonshane]

I doubt it will have an apparent effect on visuals to be honest but annoying nonetheless. I'll be keeping the scope for a long time then!

I may try and adjust it differently now I understand it but it may have to just remain as is.

[Moonshane]

Well, I was wrong. The effect on visual is pretty dramatic. It's now an unusable scope. 

I think I'll have to pay someone to sort it out or just write it off and buy something else with a better cell.

[Stu]

4 minutes ago, Moonshane said:

Well, I was wrong. The effect on visual is pretty dramatic. It's now an unusable scope. 

I think I'll have to pay someone to sort it out or just write it off and buy something else with a better cell.

What a shame and a pain, sorry to hear that Shane. Is is just very badly aligned now or are the clamshells causing issues?

[Moonshane]

Cheers mate

I am sure that the clamshell is so small it won't have an effect and that I have collimated it worse not better even though the reflections are closer now than they were to being concentric. I have just put it back in its box for now (better option than slinging it in the garden) and will make a decision in due course.

I am minded to just buy an old 80mm Ed doublet for <£200 than spend £100 or so getting it collimated for it to (presumably) become uncollimated again in the future. At least I can transfer across the Moonlite and rings etc.

[John]

I'm really sorry to hear this Shane

I had to give up on an old TAL 100 that I had a while back. Two of the spacers between the lens elements had gone missing and I just could not get suitable replacements to work at all, what ever thicknesses and positioning I tried.

Hopefully some of the Meade OTA can have some future utility.

 

[Moonshane]

Cheers guys

Out of the blue I have had an offer from one of our optical heros to have a look at my scope and see what can be done. I'll not name them here as I don't want them inundated ! But I thank them again so much. @John I did take the thing apart and all components seemed to be there and in the right order etc so hopefully my secret benefactor will be able to see what's what and correct whatever needs correcting. If not then no real harm done.

I have certainly learned that collimation of refractors, at least those with this sort of cell, is not an easy matter despite what the notes seem to suggest - unlike newt collimation. I'd urge anyone with a frac that works pretty well albeit not perfectly to think carefully before messing about with alignment.

[Timebandit]

5 minutes ago, Moonshane said:

Cheers guys

Out of the blue I have had an offer from one of our optical heros to have a look at my scope and see what can be done. I'll not name them here as I don't want them inundated ! But I thank them again so much. @John I did take the thing apart and all components seemed to be there and in the right order etc so hopefully my secret benefactor will be able to see what's what and correct whatever needs correcting. If not then no real harm done.

I have certainly learned that collimation of refractors, at least those with this sort of cell, is not an easy matter despite what the notes seem to suggest - unlike newt collimation. I'd urge anyone with a frac that works pretty well albeit not perfectly to think carefully before messing about with alignment.

Hello. That was nice of your secret benefactor. Fracs IMO are just a totally different ball game to newts. If a newts collimation is out then you can get it sorted without getting yourself into a black hole. But fracs seem to be a different ball game and unless you know what you are doing(or have a secret benefactor?) are well left alone. Trouble is you know what us guys are like it's tempting to give it just a little fiddle.  

Anyway an important lesson for all of us here moonshane don't fiddle with your frac unless you really know what you are really doing ,or know a man that does☺  

[Moonshane]

Yes indeed. I suppose the exception are the cells that adjust the whole cell in line with the tube like the one below

[John]

Thats good news and very decent of your benefactor

I'd have been very nervous buying my 130 triplet if it had not come from someone who knows scopes inside out and that I'd bought from in the past.

When I tested the TAL Apolar 125 the 6 element / 3 group design gave me some cause for concern - I'd really not want to go near the optics of that one !

[Dave In Vermont]

I'll only add to placing a piece of paper over the front of the scope before using a laser. And fix it there so it's flat & dead-center - it's easy to have it fold and move. Then turn on the laser in the focuser. You really don't want to chance a glimpse of the laser coming through the lens of your refractor!

Dave