Collimation - That Old Chestnut...

[Guest]

I want to collimate both my 8" Dobsonian and my friend's 4.5" reflector, but have never done it before. 

I've read most of the recommended tips, links and articles, but I'm concerned about attempting it and making it worse. 

Is the procedure on the smaller reflector different on the larger one? 

I'm going to order the Premium Cheshire from Auntie @FLOshortly. 

[Alan64]

Just dive into it with no holds barred.  Collimating is a gradual learning experience.  Don't expect perfection during the first attempts; but who knows you may surprise yourself, particularly with that premium Cheshire, of which I'm familiar, and would love to have one myself.  If your friend's 4.5" is at f/8, it will be easier to collimate; if at f/4, more difficult.  Of course, the 8" at f/6 will be middling in difficulty.  I ensure that the secondary-mirror is directly under the focusser, and the mirror itself circular in appearance...

Then, I begin to collimate from there.

When collimating, you want the tool in the same position within the visual-back, perhaps skewed slightly to one side when clamped, and as the eyepieces will be whilst secured during an observing session.  That ensures that the centre of the tool corresponds exactly with the centres of the eyepieces, and for the sharpest images.

[Neil H]

Hi i never found collimation that hard also take your time  dont rush .Dont make big changes a small change is easy to fix follow astrobaby guide to collimation  so far collimated 114 , 150 , 200 . They all collimate the same just the 114 was a little harder to do secondary mirroras you need to get your hand in the tube . Glad you got a Cheshire i still feel this works better than the cheap lazer does 

[MrFreeze]

I found the hardest bit was to figure how to make the adjustments - which screw does what. I also found that a cheap laser beats a cheap cheshire hands down. I couldn't focus on the wires on the short chinese cheshires - too close to my eye. If you just aproach it logically I'm sure you will be fine. I had no choice not to do it - my scope was so badly collimated!

David

[Dark Vader]

I was that concerned about collimation that I actually held off buying a scope for a couple of months, then even looked at buying a sub £300 refractor instead. I read and re read the Astrobaby guide until it started sinking in then saw some comments on here saying that unless an Allen key fell down the tube and hit primary, there was little that could go wrong that couldn't be undone.

My 200p arrived pretty much ok and with the FLO premium Cheshire, a collimation cap and the Astrobaby guide is now (I think) spot on. Go for it, it's easier than I thought it would be.

[Guest]

There's a 2nd hand one (unused) on ebay, I made an offer but it was declared - hey ho... 

[Davey-T]

I have the premium Cheshire from FLO and it's very nice just a pity it doesn't come in a bolt case with some basic instructions for the price, the cheap Solomark one comes with end cap and instructions.

Dave

[jetstream]

I like my cheap Celestron cheshire- a set of cross hairs and no confusing "cross" cut out of the reflective face,,, just saying

[MrFreeze]

If you want a cheap one - try https://www.aliexpress.com/item/33056951646.html?spm=a2g0s.9042311.0.0.48e04c4dpFyzEc . Mine just arrived today - that's just 9 days from China! And for the princely sum of £9.17 plus 60p postage. Unlike the short one I have that cost more than twice that amount, I can focus on the crosshairs on this.

David

[Colossal Plossl]

I just used a rigel collimation cap.  Takes 30 seconds

[ScouseSpaceCadet]

Best video

14 hours ago, merlin100 said:

I want to collimate both my 8" Dobsonian and my friend's 4.5" reflector, but have never done it before. 

I've read most of the recommended tips, links and articles, but I'm concerned about attempting it and making it worse. 

Is the procedure on the smaller reflector different on the larger one? 

I'm going to order the Premium Cheshire from Auntie @FLOshortly. 

This video takes the fear away. 😀

https://m.youtube.com/watch?v=YAVGcGEBmCE

 

 

[Alan64]

I use both a Cheshire and a collimation-cap, with one serving as a fail-safe for the other, in verifying the collimation.  A cap will definitely get you within the "ball park", but for that extra measure of sharpness, for the higher powers where a telescope must work harder to produce pleasing images, a Cheshire(or a simpler sight-tube with cross-hairs) serves best.  

This, the secondary-scene of my 127mm f/4 catadioptric-reflector, albeit at an effective f/8 with its integrated, correcting lens-assembly...

On the left, you can see the actual cross-hairs, and blurred; in the centre, over the primary's centre-spot, the reflection of same, and sharply-defined.  

On the right, the same, yet with the various components highlighted.  Note how the yellow circle is not quite centred within the green.  That's the secondary's off-setting, and normal for an f/4 reflector.  At f/5, the off-setting is little less wonky, at f/6 a bit less than that.  Lesser still as a telescope reaches f/8 or more, and then almost perfectly centred.  The good thing about a reflector's off-setting is that it occurs automatically during a normal collimation procedure, and without intervention on the user's part.

Once the two sets of cross-hairs, blurred and sharp, are lined up together, and both centred over the primary's spot, you're golden.  After I photographed that scene, I saw Jupiter's "Great Red Spot", sharply, and incidentally for the very first time in my life.

Our eyes are rather weak, having evolved for use during the day when there's plenty of light, and more besides; up at the break of day, then to bed as night falls.  That's why we tend to gravitate towards telescopes, and in going against the mold.  In the instance of collimation, our eyes have a difficult time looking down into a focusser.  The tiny peep-hole of the tool isn't very accommodating.  It's almost dead-black down there, for another, and our eyes cannot zoom in, like a camera, for yet another.

When collimating indoors, which is far easier, unless travelling, I like to illuminate the tube with a small lamp, and its shade overlaid with gift-type tissue secured with a rubber-band...

I then take a small point-and-shoot camera, zoom into the secondary-scene, and snap a shot, albeit through a collimation-cap in this instance...

There's no question in that one being ready for a show.

[Guest]

9 hours ago, Alan64 said:

I use both a Cheshire and a collimation-cap, with one serving as a fail-safe for the other, in verifying the collimation.  A cap will definitely get you within the "ball park", but for that extra measure of sharpness, for the higher powers where a telescope must work harder to produce pleasing images, a Cheshire(or a simpler sight-tube with cross-hairs) serves best.  

This, the secondary-scene of my 127mm f/4 catadioptric-reflector, albeit at an effective f/8 with its integrated, correcting lens-assembly...

On the left, you can see the actual cross-hairs, and blurred; in the centre, over the primary's centre-spot, the reflection of same, and sharply-defined.  

On the right, the same, yet with the various components highlighted.  Note how the yellow circle is not quite centred within the green.  That's the secondary's off-setting, and normal for an f/4 reflector.  At f/5, the off-setting is little less wonky, at f/6 a bit less than that.  Lesser still as a telescope reaches f/8 or more, and then almost perfectly centred.  The good thing about a reflector's off-setting is that it occurs automatically during a normal collimation procedure, and without intervention on the user's part.

Once the two sets of cross-hairs, blurred and sharp, are lined up together, and both centred over the primary's spot, you're golden.  After I photographed that scene, I saw Jupiter's "Great Red Spot", sharply, and incidentally for the very first time in my life.

Our eyes are rather weak, having evolved for use during the day when there's plenty of light, and more besides; up at the break of day, then to bed as night falls.  That's why we tend to gravitate towards telescopes, and in going against the mold.  In the instance of collimation, our eyes have a difficult time looking down into a focusser.  The tiny peep-hole of the tool isn't very accommodating.  It's almost dead-black down there, for another, and our eyes cannot zoom in, like a camera, for yet another.

When collimating indoors, which is far easier, unless travelling, I like to illuminate the tube with a small lamp, and its shade overlaid with gift-type tissue secured with a rubber-band...

I then take a small point-and-shoot camera, zoom into the secondary-scene, and snap a shot, albeit through a collimation-cap in this instance...

There's no question in that one being ready for a show.

I knew there'd be an offset with the faster telescopes, that's what has been stopping me from collimating because I thought the offset would have confused the situation (me). 

[Alan64]

1 hour ago, merlin100 said:

I knew there'd be an offset with the faster telescopes, that's what has been stopping me from collimating because I thought the offset would have confused the situation (me). 

No, it should not be any bother at all, for, again, the off-setting occurs automatically, with nothing for you to do.

Some do tweak it further, and for that last iota of sharpness.  There is another aspect of off-setting a secondary-mirror, and in relation to the mirror itself and its stalk to which it's attached; not in relation to the optical-system in toto as discussed previously.  But we seem to rely on that type of off-setting being done properly at the factory, however I encountered one that required correcting.

Your 8" f/6 will have an off-setting, although not as drastic as an f/5 or f/4. 

Do you know the focal-ratio of your friend's telescope?  It will be at either approximately f/4, or f/8; a short or long tube, respectively.

[Guest]

9 hours ago, Alan64 said:

No, it should not be any bother at all, for, again, the off-setting occurs automatically, with nothing for you to do.

Some do tweak it further, and for that last iota of sharpness.  There is another aspect of off-setting a secondary-mirror, and in relation to the mirror itself and its stalk to which it's attached; not in relation to the optical-system in toto as discussed previously.  But we seem to rely on that type of off-setting being done properly at the factory, however I encountered one that required correcting.

Your 8" f/6 will have an off-setting, although not as drastic as an f/5 or f/4. 

Do you know the focal-ratio of your friend's telescope?  It will be at either approximately f/4, or f/8; a short or long tube, respectively.

It's a F8, 114-900. 

[Alan64]

10 hours ago, merlin100 said:

It's a F8, 114-900. 

Then you'll see that an off-setting at f/8 is practically nonexistent, off-set very little, if at all; a 6" f/8 for example...

Again, the higher the focal-ratio, the easier to collimate; so there's some good news, and encouragement.

I have a 4.5" f/8 myself, but I haven't touched it yet, as in having renovated it, for as telescopes come from the factory, particularly the entry-level, and those bit advanced even, they can use some improvement here and there...

It's also the reflective equivalent, yea, a "doppleganger" even, of my 4" f/8 refractor.

[Guest]

20 minutes ago, Alan64 said:

Then you'll see that an off-setting at f/8 is practically nonexistent, off-set very little, if at all; a 6" f/8 for example...

Again, the higher the focal-ratio, the easier to collimate; so there's some good news, and encouragement.

I have a 4.5" f/8 myself, but I haven't touched it yet, as in having renovated it, for as telescopes come from the factory, particularly the entry-level, and those bit advanced even, they can use some improvement here and there...

It's also the reflective equivalent, yea, a "doppleganger" even, of my 4" f/8 refractor.

The 4.5 reflector is a 20 year old Meade 114-900, bought 2nd hand last year.

[Alan64]

57 minutes ago, merlin100 said:

The 4.5 reflector is a 20 year old Meade 114-900, bought 2nd hand last year.

Yes, that's when they were manufactured in Taiwan, and what I call "Free China", at present.  The mount is an EQ2-class equatorial, and just as my own...

Celestron offers a 4.5" f/8 kit, too, but it comes with the smaller EQ1-class equatorial mount; less stable, less supportive...

https://www.celestron.com/products/powerseeker-114eq-telescope

The Meade is the better value, of course.

I wish you and your friend great success in collimating the telescope and observing with it.

[Guest]

3 hours ago, Alan64 said:

Yes, that's when they were manufactured in Taiwan, and what I call "Free China", at present.  The mount is an EQ2-class equatorial, and just as my own...

Celestron offers a 4.5" f/8 kit, too, but it comes with the smaller EQ1-class equatorial mount; less stable, less supportive...

https://www.celestron.com/products/powerseeker-114eq-telescope

The Meade is the better value, of course.

I wish you and your friend great success in collimating the telescope and observing with it.

The mount is badged as an EQ-1B.  Not the same standard fittings as today, therefore not easy to get a motor drive for...

[Alan64]

8 hours ago, merlin100 said:

The mount is badged as an EQ-1B.  Not the same standard fittings as today, therefore not easy to get a motor drive for...

True that, but despite its badge, it may be an EQ2-class mount.  It is difficult to tell from the image, as I can't see the profile of the mount-head; only from the back.  Modern EQ1-class mounts are noticeably smaller, the smallest of all, and with spindly legs...

I renovated that mount, and to my liking...

That's the 127mm f/8 catadioptric-reflector that came with it.  The EQ series of mounts...

Edited October 3, 2020 by Alan64

[Alan64]

In so far as a motor-drive for the EQ-1B, this may be the one to consider...

https://www.firstlightoptics.com/celestron-astromaster-series/motor-drive-celestron-astromaster-geq-93514.html

The Celestron motor-drive kit has two mounting-brackets; one for an EQ-1(if the EQ-1B is an EQ-1 in fact), and one for the EQ-2...  

I don't know if the Sky-Watcher motor-drive includes both, or not.  This US-sourced Meade drive is from the era of the EQ-1B, and most likely would fit it...

https://telescope-warehouse.com/shop/ols/products/meade-telescope-533-ra-drive-motor-modified-as-a-531-to-fit-12-shaft-eq-mounts

However, that's just an example, and not intended for purchase, as it has been modified.  But you can see how it's practically identical to the Celestron.  

Edited October 3, 2020 by Alan64

[gurneyfan67]

When I bought my Celestron Cheshire the owner of the astronomy shop showed me how to use it on a 10" Dob and I used it to collimate my 110mm Tal Newt and the procedure was identical. It is not difficult you just need to go slowly when making adjustments.

[Alan64]

Aha!

I'm now starting to think that it's an EQ1-class mount after all, however that chromed, toothed wheel of the RA-axis is only on the EQ-2 mounts of today; stranger and stranger.

[Guest]

11 hours ago, Alan64 said:

Aha!

I'm now starting to think that it's an EQ1-class mount after all, however that chromed, toothed wheel of the RA-axis is only on the EQ-2 mounts of today; stranger and stranger.

It's not something that I'm pursuing these days, as I'm happy with the Dobsonian.😉  Back to the topic at hand...  I'll tackle the collimation on the smaller reflector first, as a trial run, then look at the Dobsonian.

[Alan64]

51 minutes ago, merlin100 said:

It's not something that I'm pursuing these days, as I'm happy with the Dobsonian.😉  Back to the topic at hand...  I'll tackle the collimation on the smaller reflector first, as a trial run, then look at the Dobsonian.

Whilst straying away, I did think that you might convey those aspects to your friend.  The best of luck to both of you.