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AlexF

Poor man's collimation tool?

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Is there a method that doesn't require any more purchases to get good collimation?

Thanks.

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Use a old 35mm film canister ( usually can be picked up for free from your local camera shop) drill or cut a large hole in the base 8mm to 10mm diameter. In the centre of the lid drill a 1mm to 2mm hole.

This can be placed in the focuser, instead of the eyepiece, and used to center your eye during collimation. The secondary, main mirror and inside the focus tube should all appear concentric when you're finished. Check by looking at an out of focus star image - should appear evenly illuminated with the dark circle ( the outline of the secondary) in the middle. When you bring the star closer to focus there should be no "rays" or flares to the side etc.

All this for no additonal cost, other than a bit of time and effort.

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If you can afford £6 get a collimation cap. Does the same as above plus you can adjust the primary as well.

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I think in use the collimation cap only differs from a film canister because it has a white transparent face, enabling you to see the centre of the focus tube when collimating. This can be sorted by using a white transparent film tube.

I have one availabe to post to you if you like, FOC.

Andrew

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With my 8-inch dob I always used the film cannister method and it worked well enough (on the comparatively rare times when I needed to collimate).

On a 6-inch, which I believe you have, it should work just as well. Once you're collimated then it should stay that way for a very long time (months or years depending how unfussy you are) unless you remove mirrors for cleaning or give the scope a serious bump.

The cannister has drawbacks, of course. You've got to use your own judgement about when things are centred. And if you need to move away from the eyepiece to adjust the primary (as I had to with the long-tubed 8-inch) it's very hard to work out which way things are moving when you twiddle a primary knob. In practice it makes it a two-person job - you look through the eyepiece while your assistant adjusts the primary. (My wife and kids were glad when I invested in a cheshire.)

But for a 6-inch owner on a tight budget, I'd say stick with a film cannister.

Just a thought - has anyone tried adding cross hairs to a film cannister? It would make for greater accuracy - if your eye can focus on them.

If you do end up spending money, get a cheshire rather than a laser. But you really don't need to.

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But for a 6-inch owner on a tight budget, I'd say stick with a film cannister.

Quite adequate if you have the common sense to get a long focus scope in the first place - an f/8 scope is several times easier to collimate, the "sweet spot" is much bigger and the fall off away from it much slower.

You'll end up fine tuning the collimation on a natural star in good seeing anyway. With an f/8 scope, you'll probably find you have it pretty well nailed with just the colli cap. With an f/5 scope, a Cheshire type collimation tool is pretty well a necessity, as is a good sense of humour and/or an infinite supply of patience.

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Eeeee bye gum when I were a lad we used to use a cotton reel. Already has a hole in it for looking through, its round and some come in white. No purchase necessary if wifey has one in her sewing basket. Folks do still have sewing baskets these days don't they:D

philjay

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With an f/5 scope, a Cheshire type collimation tool is pretty well a necessity, as is a good sense of humour and/or an infinite supply of patience.

And of course...with an F4.5. scope you need other dodges !

I used to think that collimation was something they only taught to the Jedi but I'm now of another opinion - It's nothing to worry about - just take your time and read up many of the guides on the interweb

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With my 12" f5 flextube I find both a laser and a cheshire essential, the laser to adjust the secondary and the cheshire for the primary, a job I do every time I use the scope.

It is indeed very quick and simple (couple of minutes) with the right tools. Without them it can take forever, which is why a modest aperture scope, f6 or slower, is the right sort of thing for people who don't want to spend time or money getting their collimation spot on.

In practice I'd say it means that anyone who doesn't want to fork out £20 for a cheshire should limit themselves to 8 inches of aperture maximum, in which case a film cannister will be good enough. Anyone who can afford to go larger can presumably manage the small added investment.

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anyone who doesn't want to fork out £20 for a cheshire should limit themselves to 8 inches of aperture

Which of course is tosh! An eyeball will get you close enough with a cannister/hole for just about any scope. Then, as Brian says, do the final tweak on a star. Was plenty good enough for the Blue, and even when I knocked up the laser collimator it was still first method while the laser got used later in the dark.

Arthur

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Fair enough, Arthur. Think we'll agree that the poor man's collimation tool is a star.

But I certainly don't regret spending £20.

And Brianb's point is that a cheshire is essential for f5 or less, though I understand from another thread about the Blue being for sale that it's f4.76.

http://stargazerslounge.com/heads-up/87626-got-4-grand-spare.html

A magnificent looking scope indeed - you must have had great times with it.

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I did, and I do not regret using/paying for a 10mW laser for the collimating tool either - but the point is that the Mk1 eyeball and a bit of plastic is the cheapest option - after that you spend what you can afford to decrease collimation time - not necessarily ease though!

Note the comment about the dark though - collimating cannister not so good in the dark... dark almost demands a laser of some sort.

Arthur

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I take your point about the dark. With the cheshire, I shine my red light onto the reflecting face while looking through the eyepiece, then I can see what's going on. But it's not ideal, and moving the illuminating source can sometimes make the image seem to move a bit. A little light attached to the cheshire might help, shielded so it doesn't shine into the eye.

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