collimation blues

[JimmyH155]

I am a bit confused about collimation procedures! Having become the proud owner of a Lightbridge 12”, I have used it a few times and have been reading all sorts of conflicting advice about how to collimate, when to collimate etc. When I first assembled the scope, I peered into the eyepiece hole as instructed in the Instruction Manual and couldn’t find anything wrong at all. Next outside to the star test, and last night (at last the Moon has gone) I put a 12mm eyepiece in and pointed at delta Crux. I defocused as instructed, and on one side of the focus, the black bit was dead centre, but when I turned to the other side of focus, it was a little bit out to one side. Does this mean I should fiddle about with the primary mirror a bit? The stars still look in focus ok – ie the Jewell box looks terrific and even the tiny stars look in focus…
Now my question…. In the Dec 2005 AS & T there was an article on collimating your Dob. The writer said that the 3 locking screws on the primary mirror are not needed and should be ignored. They even say take them out altogether. Other instructions on the Web, say loosen all three lock screws first before adjusting. The Meade Instruction Manual fails to mention what to do with the locking screws. As for the secondary, (Heaven forbid I should have to do that!), I have read how you must never touch the central screw, how you Must always undo it before adjusting the other three – which is correct? As for the primary, the mirror surely cant only just rest on the spring adjusters can it – it would bounce around as you turned the scope…..

HELP / ADVICE please.

[slice of heaven]

G,day Jimmy
The 3 lock screws make it harder and more time consuming than it needs to be.
I removed mine on the gs 12" within the first couple of days and replaced the standard springs with heavier ones that can hold the weight of the 12" mirror. If the l/bridge uses the same springs as the gs, maybe someone could contact Meade and see if they can address the problem by fitting suitable springs as standard.


PS. A temporary quick fix is to screw the collimation screws in to compress the springs, then adjust to collimate and the compressed springs won't allow the mirror to float around as much.

[davidpretorius]

Defocussing with the black dot is say step 1, generally yes, you would like to have it nice and centre for both sides of focus. I would remove the 3 locking screws as they serve no pupose. Only leave the 3 x collimation screws.

For the beginnner: http://www.schlatter.org/Dad/Astronomy/collimate.htm
Advanced: http://legault.club.fr/collim.html

Without tracking it can be harder, but as higher magnification as you can. I have a 5mm vixen and then i slightly defocus and try and have nice concentric rings.

Hey it takes many nights to get the hang of it. ie if i turn one of the collimations screw, what actually happens, am i making it better or worse??

It just takes practice

[janoskiss (Steve H)]

Watch this:
http://www.andysshotglass.com/Collimating.html

Don't be scared of collimating. With a truss dob I would not be surprised if you had to tweak the secondary more often than with a solid tube. The locking screws will be needed if the springs the mirror is resting on are not stiff enough (they are not on my 12" GS Dob - out of same factory as the LB).

[EzyStyles (Eric)]

steve talking about collimation, where did you get your collimator from and how much was it?

thanks

[astronut (John)]

Steve, It's good to have another Lightbridge on the block.
If you haven't bought a collimator yet, BUY ONE NOW!!!
I've only ever used a refractor, so when it came to a reflector I was about collimating.
A very experienced Telescope maker in our club told me to forget about the new fandangled lasers and buy a cheshire.
I purchased the Orion from Bintel ($69) and followed the very easy and precise instructions.
Now with the new collimation hand operated knobs, even a dumb b.....m like me finds collimating simple. Trust me

[janoskiss (Steve H)]

Originally Posted by EzyStyles

steve talking about collimation, where did you get your collimator from and how much was it?

I got the celestron one from York, $69 also. The Orion one from Bintel is exactly the same.

[Starkler (Geoff)]

I find the Orion type preferable to the other common Synta one for the reason that its a better fit in the focuser. The Synta one is a bit of a loose sloppy fit.

[Gargoyle_Steve (Steve)]

I also have the Orion combo sighting tube / Cheshire, $69 unit - for a newbie like myself especially it increased my ability to collimate more accurately, and radically decreased the amount of time it takes me to do it. SO worth $69 when viewing time is so precious.

[rmcpb (Rob)]

Get a good cheshire from either of the above suppliers and follow the instructions.

Don't be afraid of collimation it is a must do if you have a reflector. Basically you centre to secondary in the focuser by using the large centre screw, centre the primary in the secondary by using the three small screws on the spider, then centre the secondary in the primary by using the large collimation screws on the mirror cell.

First time you do it it will be a real pain but then you will start understanding it , then its a quick tweek each session and you are away. Have a go, you will be surprised how easy it becomes.

[Starkler (Geoff)]

I find that a laser collimator comes in very handy for aligning the secondary and well worthwile in addition to the cheshire if you take your lightbridge apart much.

If you do get a laser also, you should make a v-block and ensure that IT is also collimated.

[janoskiss (Steve H)]

I would only buy a quality laser; not like most of the ones in scope shops. My laser collimator ceased up when I tried to collimate it. My guess is that if the collimation screws scratch the paint on the barrel of the keychain type laser inside you get a short circuit.

[astro_nutt]

I guess owning a truss-tube scope has an extra set of rules...
Prior to collimation...mark the top and bottom housing with a permanent marker where the trusses connect..eg..A to A..B to B..(use a white paper stick-on label on the paintwork first!)
I use a Chershire collimator first off then fine-tune with a laser..another trick with a laser is note where the beam strikes the primary mirror with the focuser fully in and out...if the beam shifts..then your focuser is loose or not squared in!..
If your EP holder in the focuser has the 'ol 2 screws..then secure the collimator in the same as you would your EP's..eg..right screw first..left screw last...The amount of gap play does make a diffrence!!
As for the locking screws for the primary mirror..it's a matter of choice..but you should only have to turn them until you feel resistance against the mirror cell.
Collimation does get easier the more you do it.

[Starkler (Geoff)]

Originally Posted by astro_nutt

I use a Chershire collimator first off then fine-tune with a laser.

.

To varying degrees you can collimate your primary to the laser, try the cheshire again and find yourself out of collimation
It is too easy to introduce errors using a laser this way, and there is much written on this topic.
The cheshire doesnt lie and should be the reference, unless you use the barlowed laser method.

another trick with a laser is note where the beam strikes the primary mirror with the focuser fully in and out...if the beam shifts..then your focuser is loose or not squared in!..

I use the laser to adjust secondary tilt so that the dot hits the centre of the primarys centre spot. This ensures that the optical axis is aligned to the focuser axis, so that the focal plane is flat and the primarys collimation point shouldnt change with changes in focuser position.