Collimating query.

[scagman (John)]

Hi everyone,

I am trying to work out if my OTA needs collimating.
I have a loan of a collimator and when I insert it and look down the OTA (I leave the cover on the OTA) I see 2 circles. These circles aren’t completely overlapping, they are offset a bit so I assume it needs collimating.
Around the aperture end, there are 4 sets of 2 small screws.(See attached pic)

Are these the screws for adjusting the collimation? If so, Do I just adjust them till the circles overlap?

Thanks for any help
John

[mental4astro (Alexander)]

Hi John,

First, what scope are you trying to collimate, Newtonian, SCT, refractor, and what's the collimation tool you are using?

[scagman (John)]

Hi Alexander,
The scope is a 127mm ED APO refractor, and the collimation tool is 1 made by rodger from Bintel.
Its about 5" long, fits in the 1.25" barrel, has a large hole on the side with a mirror on a diagonal and a pin hole in the end you look thru. Light comes in thru the hole on the side, hits the mirror then goes down the ota tube.(see attached diagram).

Hope my pic helps.

John

[asimov (John)]

The 2 circles should be merged as one, yes. As to the screws you refer to, I have no idea. I have a 'non collimatible' ED80 that I had to collimate by shimming between focuser body & the end of the tube.

[casstony]

John, don't touch the screws in your photo - they are for centering the elements in what looks like a triplet? You really need to know what you're doing before playing with those.

There should be three sets of push/pull screws on the front of the cell that you can use for collimating the lens cell with the tube. If you did get things out of whack here it could easily be fixed at Bintel. Here is a guide: http://www.spacealberta.com/equipmen.../collimate.htm

Note: Not all refractors have push/pull screws for aligning the lens cell with the tube.

[bmitchell82 (Brendan)]

i would not touch anything at all... That looks like a newtonian collimator. Do a star test at high magnification that will tell you how well aligned your cell is. I would say unless something is really off key then leave it alone.

[scagman (John)]

Hi Guys,
Thanks for the warnings.
I think I'll wait till I go back down to Bintel and get them to have a look as I cant see any other screws such as described by Tony.

I'm pretty sure it is the right type of collimator as rodger from bintel knew I would be using it on a ED APO. I will do a star test once the mount arrives( dont you hate the wait).

Once again thanks for the advice
Regards
John