Refractor collimation

[Moonshane]

I have never collimated a refractor but the images I have been getting with my 80mm  f6 Meade triplet have been a bit soft at anything above about 80x and there's a slight flare one side of the focused image. So, I checked last night and it seems it is out of collimation. See image below.

Unfortunately I don't think this scope has a collimatable cell although it's possible the two screws in the main body of the cell will allow some lateral collimation? That said, the sort of collimation I need appears to be axial. There are also three grubs in the front ring (with writing on which seem to allow the front ring to be rotated or perhaps even removed but I decided against this.

I did manage to adjust the focuser alignment to gain a more or less good collimation but what this did was tilt the focal point so much that it resulted in the aperture being clipped.

I have now restored it to how it was. Other than making (or getting someone to make) an attachment to allow collimation of the cell, does anyone have any ideas please? I cannot really understand how a cell (and a focuser - albeit this is aligned well when restore to standard) that screws onto the OTA can be so far out.

Cheers

Shane

 

[Moonshane]

ps, the odd silver reflection in the first out of collimation pic is because I forgot I had a IR/UV cut filter in the scope!

[ronin]

Quick search and :- Is yours a series 5000 or 6000 ?

There is or was a write up of the 5000 series Meade 80mm APO on CN that says the lens cell is collimatible. Paragraph says:

Available in 80 and 127mm objective diameters, the Series 5000 triplet apochromats boast fairly short focal ratios, f/6 (480mm) and f/7.5 (953mm) respectively. With machined aluminum Crayford focuser, retractable dewshield, screw-on lens cap, and collimatible objective cell, the Series 5000 apochromats have what can be considered these days as a standard feature set.

Not seen, so far anything about the series 6000. Although I would have thought they kept the collimatible cell, not really the sort of thing you drop, and I seem to think that Meade generally put a collimatible cell on their refractors.
CN Review S5000

[ronin]

Bit more sort of general info:

Meade4m

Say "general" as at the end of the artical not sure if it is or is not collimatible. Get the idea the person gave up and just accepted what he had.

Seems that artical also refers to the 5000rseries. Maye useful to search out the ES data and manual on their similar item.

[Moonshane]

cheers Ronin

I have done a fair bit of googling but can see no definitive answer either. The problem I have is not wanting to make matters worse by loosening what appear to be lateral control screws.

[andrew63]

This is the manual for the es 80 triplet, which comes from a lot meade stuff. If you look about have way down it mentions collimation and how to do it, the diagram of the cell looks like your image Shane.

 

http://www.whcamera.com/media/downloadable/pdf/Explore_Scientific_Triplet.pdf

 

andrew

 

 

[Skyline]

You could always send the lens to Esmond Reid for collimation. If that helps.

 

Al.

[Peter Drew]

Shane. In my experience it is usually the central biconcave lens element that causes the collimation issue that you describe. This component is very sensitive to lateral centering and produces a comatic appearance normally associated with a doublet that is tipped laterally. Very small adjustments have an enormous effect so be careful if you attempt this.

[Peter Drew]

Edit.    Tipped axially!

 

 

[Moonshane]

Cheers all. I'll have a look this weekend when I have more time for fiddling.  The es guide Andrew posted might really help. Let's see what happens :0)

[spaceboy]

It looks a similar setup to the Tal100R which I think John had a go at collimating. Can't remember what the outcome was but you could PM him to see if he has any advice I guess.

[Moonshane]

cheers all 

I couldn't resist last night and had a look (albeit didn't attempt collimation). One of the little grubs referred to as being for collimation in the document kindly posted by Andrew was very loose so hopefully explains the problems I am having. I'll have a go at collimating it this weekend after having a proper look at a star test first as a benchmark. For now I just took up the slack in the loose one. Thanks again everyone you've been a really big help as always. I'll report back once I have done this and maybe take some more before and after (and maybe even during!) in case it helps anyone. Hopefully it's a tiny tweak, first time, in the right direction 

[Stu]

Just a note that the ES instructions suggest starting at the rear cell, but Peter's experience is that the centre cell is the most sensitive to adjustment. Might be worth some tiny tweaks on the centre first to see how you go? Which cell was loose?

Good luck chap!

[Moonshane]

Agreed Stu and I had noted that (thanks Peter). In my scope the cell is like this (I seem to be finding loads more resources today for some reason!)

with one set of grubs in the front ring and two in the middle ring. The one that was loose was in the row to the right of the one he has the allen key in so it looks like it is the middle element. the fact that little changes makes a big difference is a good thing too as I could not understand how I could possibly adjust out anything like the level I had to do in the focuser. Worst case scenario is that I fiddle and cannot correct and then have to pay someone to get the collimation smack on. Not the end of the world as I reckon it will be much enhanced by this exercise. Whilst I bought it as a wide field / white light frac for hols, it would be nice to do some planetary / doubles with it too. 

[John]

The scopes are able to perform to a high level when "on song" so worth the effort and a little expense I reckon.

Meade have struggled with lens cell design in the past though - their ED doublets (4" - 7") back in the 1990's were notorious for shifting lens elements. Once modded a little they can be sterling performers though.

Imagine what collimating one of the quad or quint refractors must be like !

[Moonshane]

True indeed John! I think I might put a little blob of something in the holes once set to prevent the grubs from turning. Then again, once I get the idea of what to do I think it will be straight forward enough to repeat. My main concern was that I was not 100% sure what the grubs did and I didn't want to start fiddling before I did. This thread has definitely confirmed that the cell can be collimated and that it appears possible to do. Unless I am missing something, do you really need a laser to collimate the focuser? Surely a cheshire can be use for this in the same way you'd centre a secondary in a newt focuser?

[John]

I found a laser collimator (collimated !) a convenient way to check that the optical axis of the focuser is in line with the optical axis of the objective. As I understand it, if the laser exits the objective pretty much through the centre, then things are in good shape.

 

[Moonshane]

cheers John

I don't have one and my logic was if I use a Cheshire and the end of the cheshire is concentric with the objective then it's the same thing.

[spaceboy]

A laser sounds the way to go as you can see there and then what effects the tightening or loosening is having. A Cheshire is great but you have to adjust then faff back and forth looking through it and even then there is no saying your eyeing it up the same every time. As a dob owner as well its not like it wouldn't have its uses long term if you were to invest in one.

[Stu]

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

Stu

[Peter Drew]

A laser will give a good quick check to show if the focuser is squared on, I don't think it will be much help for judging the collimation of the objective though. The changes due to tweaking the adjustment screws can be seen only on a real or simulated star test.

[John]

1 hour ago, Peter Drew said:

A laser will give a good quick check to show if the focuser is squared on, I don't think it will be much help for judging the collimation of the objective though. The changes due to tweaking the adjustment screws can be seen only on a real or simulated star test.

Yep - thats exactly what I've found

[spaceboy]

Can you not collimate a refractor with a laser collimator then ?? I was sure you could! I'm sure I have read it somewhere ?? Or am I thinking of a mak ?? I can remember it has something to do with paper over the objective so I don't think it was a mak ??

[Stu]

9 minutes ago, spaceboy said:

Can you not collimate a refractor with a laser collimator then ?? I was sure you could! I'm sure I have read it somewhere ?? Or am I thinking of a mak ?? I can remember it has something to do with paper over the objective so I don't think it was a mak ??

I think, as Peter says, what you can do with a laser is check that the focuser is correctly aligned and shim it if it needs it.

[spaceboy]

At least there were members better informed so as to have saved Shane wasting his money

I have had a look to try and find what I read. I think this was it if I remember correctly http://philjay2000.tripod.com/usefulstuff/adventures.pdf but either case I was wrong. Why it stuck in my mind that you could I'll never know ???