Newtonian Collimation

[Astronut]

I've just been reading a review of a selection of 6 collimators (3 laser, 3 cheshire) in the latest edition of Sky at Night.

The Orion cheshire is the overall winner in the review and the Skywatcher cheshire wins second place in the 3 cheshires reviewed. The Orion won out over the Skywatcher mainly because it has a brighter 45 degree reflective face and is supplied with instructions (no big deal as there's plenty of information online anyway). Out of the cheshires, the Astro Engineering one was let down by having a too large peephole (4mm compared to the 2mm peephole in the Orion and Skywatcher cheshires) and by having a too small hole for the reflective 45 degree face.

Out of the laser collimators reviewed the Baader is the winner and came 2nd place overall. The laser aim is easily adjustable and instructions are supplied but the only thing about it that puts me off is the barrel that fits in the focusser drawtube looks a little short and may, as a result, not fit as snugly into the drawtube as the cheshires which seem to have a much longer barrel negating any side movement rocking in the drawtube. I would think that any side to side rocking movement in the drawtube would make a laser collimator next to useless. Just how good a fit in the drawtube is the barrel of the Baader laser collimator? Is it something that I should be concerned about if I decided to get one?

I've read various articles on collimation and I'm leaning towards a cheshire collimator (simpler, cheaper, more accurate) but for the 12" Lightbridge I'm ordering soon I'm thinking a laser collimator may be the better choice purely for ergonomic reasons: ie. not being able to reach the primary screws from the eyepiece when using a cheshire.

Also, I'm thinking if I were to transport the 'scope to a different location, a cheshire may not be much use in the dark (unless I used a torch to illiminate the 45 degree face).

I understand the principles of collimation and I remember doing it a few times 20+ years ago with a home made cap but....

what if the focusser itself is not alligned correctly ie. not perpendicular to the tube axis and/or not in-line with the optical axis from the secondary?

All the collimation FAQS I've read concentrate on the secondary and primary allignment but none seem to mention the focusser drawtube allignment.

Some focussers (like the Moonlite) have allignment screws at each corner of the base so how are these used in the collimation process?...

....or is the focusser alignment automatically taken care of by the normal collimation procedure in that the optical axis is alligned to the focusser's drawtube axis regardless of the focussers initial alignment?

Does that make sense? :?

[barkis]

The way to ensure your focuser is at 90 degrees to the scope tube, would be to have sleeve machined almost the length of your focus tube. A small hole would be drilled centrally and all the way through obviously. A top Hat configuration would prevent it from going too far through and hitting your diagonal. It's what I used when I had a Newt. and it works a treat.

Ron. :Dl

[proflight2000]

I put the moonlite cr2 on my skywatcher 200 and it went in fine, the only issue is because I want it for picture use i need a smaller spacer so that the inward focus is better. Steve has ordered me one from the states. I have actually asked steve to supply me with a baader laser so I will let you know when I use it. But as for play, the adding of a bit of tape around the collimator does the trick, stops movement etc. Certanly steer clear of the astro engineering laser as to be totally up front, it is gak. I got the cheshire collimator when I ordered my scope and I find it is very easy to use, great instructions and after use I star collimate and it always seems fine.

My aim with the laser is basically to ensure the primary and the secondary are in alignment, plus its a gadget and boys like toys.

[Astronut]

...its a gadget and boys like toys.

My sentiments exactly I may end up getting a cheshire and a laser purely for that reason.

[mhc]

And with my typical newbie good luck I bought the AE collimator shortly before the magazine came out. Perhaps that's why my collimation sucks?

[Black Shuck]

As a newcomer I still prefer to collimate by eye (with a collicap). The issues raised with laser alignment put me off and the S@N review confirmed my fear. I have just got a new Moonlite focuser - I noted that the instructions mention that the tip and tilt can be adjusted in order to collimate on its mounting plate. It installed fine and I haven't noticed the need to adjust this - perhaps I need to have a closer look??

By the way is your post script a Rush lyric? "Territories" by any chance?? 8) (One of my favourite bands)

[Astronut]

As a newcomer I still prefer to collimate by eye (with a collicap). The issues raised with laser alignment put me off and the S@N review confirmed my fear. I have just got a new Moonlite focuser - I noted that the instructions mention that the tip and tilt can be adjusted in order to collimate on its mounting plate. It installed fine and I haven't noticed the need to adjust this - perhaps I need to have a closer look??

By the way is your post script a Rush lyric? "Territories" by any chance?? 8) (One of my favourite bands)

Yes it is indeed from Territories (album Power Windows): lyrics by the drummer Neil Peart (aka the professor)

I've seen Rush live a few times now but they don't seem to visit UK much these days or maybe I'm not paying much attention these days. Amazing live band - musos extraordinaire.

back on topic:

I've had this page http://www.backyardvoyager.com/CollimationFAQ.html bookmarked for some time now and this one does indeed mention focuser alignment. I've only just got around to reading the whole article in full and it's well worth reading.