Collimating refractors

[neil phillips]

Hi guys i just purchased two refractors from here recently. A Bresser 127 F9.5 And a Altair starwave 102 achro F11. First question, the journy was quite long via postage. So if i need to collimate. Does anyone know if the Starwave can be collimated ? it doesnt look like it, that i can see. If not how well do they hold collimation ? via things like postage ?

I can see the Bresser can be collimated. I dont intend to do anything untill i have done some star testing. But if the journy has knocked it out. How do i collimate the Bresser, has anyone ever attempted it. Or know how its done. Cheers in advance for any information.

 

 

Edited August 14, 2021 by neil phillips

[alan potts]

I have a number of refractors and all have traveled massive distances as most start in China. I person feel they hold collimation extremely well and any adjustment is a skilled job ( particularly with triplets ) and is best left alone.

Alan

[NGC 1502]

Generally speaking refractors hold collimation very well, and some people favour refractors for that reason alone.

Assuming a refractor has been properly assembled during manufacture then I’d expect it would be fine when received unless serious abuse had happened.  The condition of the packaging should give a good clue about how well or otherwise it had been treated during transportation.

You’ve mentioned you won’t do anything until you’ve star tested, and I think that’s essential. Hopefully all’s well. Of course if you’re using a diagonal it’s possible that was incorrectly assembled or suffered damage at the same time something happened to the main instrument.  Observing straight through without the diagonal would eliminate that, uncomfortable but you’d only need to do that once.

So if it were me, I’d star test, probably it’s all ok. If not, repeat the test to make absolutely certain there’s a problem before considering what to do.

Ed.

 

[wookie1965]

A star test is essential I have three Refractors one a Meade 127mm came with something wrong I enquired on here and took it to a brilliant and welcoming man Peter Drew he did a star test on a artificial star  and diagnosed that the glass was the wrong way round. It is a achromatic having a crown and flint combination one was in the wrong way he turned it around put it together and did a star test again I have never looked back.

one thing you can try is make a cover for the front out of paper same circle size just leave tabs in four places i.e. 12,3,6 and 9 o'clock  use the tabs to secure to the front of the scope, now take a laser collimator and put it in straight through without diagonal you will see where the laser hits on the paper, turn the laser 180° check again now do the same with the diagonal if it is then way off you will know the diagonal needs adjusting.

[John]

I've collimated quite a few doublet refractors, including a Bresser 127L. If the star test is good then don't worry about it. If not then I'd be happy to post about the process. A well collimated laser collimator and a cheshire eyepiece are very useful tools to have during the process.

Some refractors incorporate collimation adjustment in their objective lens cell design and some don't. The Bresser, as I recall, does, The Altair probably not although the mechanical tolerances of the Altair are likely to be higher which will, hopefully, mean that it's collimation will not need adjustment.

 

Edited August 14, 2021 by John

[Piero]

The cell holding the lenses is collimated by the manufacturer. You should not try to adjust that as this might void your warranty.

It is possible to collimate the focuser. Not all focusers are designed for easy collimation. Focuser collimation involves the adjustment of certain small screws in order to make sure that the drawtube is orthogonal to the light path. Specifically on refractors, the only focuser I collimated was the helical focuser in my TV-60 and the collimation was generally done with a Glatter laser collimator plus square attachment, although it can also be done on a star field. It generally reveals as unbalanced field curvature. When severe, it also shows unbalance field illumination and vignetting. Although focuser miscollimation can be a bit annoying, it does not affect the optical performance of a telescope, it the sense that you can still observe with it.

On refractors using standard focusers, I would not generally worry it, unless a star test or general observing shows otherwise.

Edited August 14, 2021 by Piero

[John]

8 minutes ago, Piero said:

The cell holding the lenses is collimated by the manufacturer. You should not try to adjust that as this might void your warranty.

 

The Bresser 127L, like it's Meade forebears, has a push pull collimation system built into the objective cell design.

Moonlite focusers come with tilt adjustment screws but I agree that most refractor focusers don't and need to be shimmed or have their attachment point screws tweaked if their optical axis is not square with that of the objective.

The optical axis of the focuser is the first thing you check and, if needed, sort out in refractor collimation, before going on to check the tilt of the objective lens.

 

 

Edited August 14, 2021 by John

[neil phillips]

Thanks for all the replies guys. Much appreciated. I should have said i know about the cheshire and laser focusser collimation. So will be testing that as soon as i have made the front collimation template.  I dont have a printer. So might make one by drawing around the dew sheild. finding the centre point. and using a collimated laser. 

John. Will test the bresser after collimating the focusser. If anything is up. will post a update. 

Once again thanks for the useful replies it helps. Scopes will be doing some lunar and planetary imaging. in due time. Cheers