Collimating first telescope

[snarkyboojum (Adrian)]

Hi guys,

Just posting this for some feedback. I recently bought a new 10" Dob from Bintel, and put it together. Other than a missing screw for the base feet (which Bintel kindly replaced), it was easy to put together. I haven't had a chance to actually use the scope yet, but that's another story (inclement weather etc).

When I unpacked the scope initially, I stupidly moved the collimation screws at the bottom of the base of the OTA. I didn't move them much, but thought I'd buy a collimating device for the scope to be sure all mirrors were in alignment, so I picked up an Orion laser collimator.

I read through the instructions and worked out how the collimation should be done. When I used the collimator, I realised (with some surprise) that the collimation was WAY off. It required adjusting the primary and secondary mirrors substantially to get right.

Given that Bintel told me these scopes are collimated accurately before being sold, I have some doubts that I've done things correctly (despite how obvious the collimation process is), or perhaps that this scope wasn't collimated in the first place. It also doesn't give me confidence that when I asked how the collimator was used prior to buying it, a sales guy at Bintel explained "how to use it", which involved screwing off the cap for the battery compartment "so you can look through it". In other words, he gave me *completely* the wrong information!

Does anyone have any advice, or similar experiences? Is it worth calling Bintel and talking to them and taking the scope in to check collimation?

Cheers in advance.

[alistairsam]

Hi
Have you collimated the collimator?
Keep the laser on a v groove and rotate it so the laser stays at the same point on the far wall when you rotate it
There should be three locking bolts for the primary as well. That usually prevents the primary from moving during transport.
Can't speak for bintel though.

[snarkyboojum (Adrian)]

Haven't collimated the collimator yet. It looks slightly off to me, so I'll have a bash at that too. Thanks for the tip.

[Shiraz (Ray)]

yep, you really do need to adjust the collimator. The last GSO collimator I got looked like it had been assembled by hammer. The adjusting screws on the side of it were loose and the laser assembly was flopping around. Totally useless, but it worked fine when it was adjusted up. Alexander posted a nice summary of how to do it.. http://www.iceinspace.com.au/forum/s...ad.php?t=75601

[snarkyboojum (Adrian)]

Also, seems to me that I've neglected to make sure that the secondary mirror is aligned with the focuser drawtube. I don't have anything to check that, so I guess I need *another* piece of equipment - a sight tube and/or a Cheshire eyepiece...

I'm a bit bummed that everything is so poorly adjusted given assurances to the contrary at the shop. Oh well, such is life.

[Shark Bait (Stu)]

Originally Posted by snarkyboojum

Also, seems to me that I've neglected to make sure that the secondary mirror is aligned with the focuser drawtube. I don't have anything to check that, so I guess I need *another* piece of equipment - a sight tube and/or a Cheshire eyepiece...

I'm a bit bummed that everything is so poorly adjusted given assurances to the contrary at the shop. Oh well, such is life.

To get it very close to the correct position, drill a small hole, dead centre in the end cap. Fit the end cap to the focuser and look through the small hole to position the secondary.

It will all come together. When I first got my reflector I had some trouble with collimation. With a bit of practice it will take you less than one minute.

[alistairsam]

The film canister with the hole at the end works well for centering the secondary.
I use a 1.25" adaptor in a 2" adaptor and eyeball it by looking from around 20cm or so above the adaptor. I center my eye so the adaptor end is centered, and then adjust the secondary.
Also, the coloured paper under the secondary and between the primary and secondary also helps centering the secondary.
good tutorials by astronomy shed here.
http://www.youtube.com/watch?v=zd-fl9SEYHw

I actually prefer the collimating eyepiece to the laser.
http://www.bintel.com.au/Accessories...oductview.aspx

But you'll be fine if you center the secondary correctly and then use the laser, that's once the laser is collimated as well.
Also for a very rough idea, use the reflection of your eye above the focuser.
it should be centred in the primary and secondary. I normally start with that to see how far it is.

[barx1963 (Malcolm)]

OK 2 things first.
1. Bintel may have collimated the scope, but that doesn't mean it hasn't moved out of collimation since. I have to collimate my scope each time I move it, having said that, I would be surprised if it was way out!
2. A laser is really only the last step in the process. It is quite possible to have a scope badly out but still showing up on the laser as OK.
Here is a good guide to basic collimation that I have found very useful.

http://www.astro-baby.com/collimatio...on%20guide.htm
Follow this procedure then check with the laser.

Malcolm

[Varangian (John)]

I usually drill a very small hole into the middle of a film cannister lid, insert it into the eyepiece and make sure you can see all 3 (or 5) screws on the side of your primary mirror as you are looking through the small hole you've drilled. The hole only needs to be a few mms. If you can see all screws around the primary then your secondary is close enough. I then get a cheshire collimator and look through the small hole again. It is then a matter of adjusting the primary knobs behind the scope until the two round dots you are looking at through the cheshire match up.

That's going to get you close enough and much closer than a laser collimator IMHO. Clear skies.

[ColHut (Colin)]

You might invest in a simple combination Cheshire available at any good astro shop. Here is one such:

http://www.bintel.com.au/Accessories...oductview.aspx

But you can get them nearly anywhere. Then just follow the instructions or do a search, or call back here if you get stuck.

Honestly, with a few noteworthy exceptions the combination cheshire will meet all your needs and give you reliable results.

regards