collimating

[Hootsitabernacle]

I have just flocked my 8" Dob and I think the collimation has gone to pot..i got a laser tool but I think THATS out as well!..i have no idea if the primary is out..or the secondary..or both..advice please??

[malc-c]

Depending on the make, most lasers need setting up. This can be done by using a simple jig made from waste pipe, wood or anything else that will support the laser in a horizontal plain. You simply place a sheet of paper with a dot marked using a marking pen a few meters away and rotate the laser in the jig. If the laser is out it the dot will move in a circle. You then heed to finely adjust the two screws that support the laser diode until the laser dot remains in the pen mark when the laser is rotated in the jig.

However it's best to use either a home made collimation cap or cheshire collimator as well to ensure you have the optics lined first and then use the laser to set the squareness of the optical path.

[Scott]

cheshire collimation tools are the way to go.... as I'm sure you'll all agree :D

[Astro_Baby]

Lasers are not good when you have gross collimation errors. Best to do the thing by eye to start with. Its possible to do it roughly with no tools at all to start with and then use the laser when you are close.

[steppenwolf]

Hmm great potential for a laser v Cheshire debate here but we mustn't take over the original thread! Here's the jig that I use for my laser calibration - never use a laser unless you have collimated it yourself!

[Scott]

Hmm great potential for a laser v Cheshire debate here but we mustn't take over the original thread! Here's the jig that I use for my laser calibration - never use a laser unless you have collimated it yourself!

You're right Steve and although my comment was meant to be a light hearted view of the l v's c debate I can see how it could detract from the origional post. Sorry for that Gordon (?). I guess my main advise would be

1/ check that the secondary is centred (using a tape/rule)

2/ primary to go back in the same position as it came out although this could be hard if it wasn't marked on removal

3/ find a guide you understand and trust and stick with it ( I like Astrobaby's but some don't) It's a personal choice I suppose

[Astro_Baby]

You can work without the Chesire by eye to correct the mirrors.

Step 1

Look down the focu tube and get the get the seckndary showing round and circular and centred to the focus tube. This step is easier if you put a but if card down the telecope tube to block the primary mirror refelections. Get the secondary square and showing round to the focus tube.

Step 2

remive the card from down the tbe if you put it in during step 1. Now with your eye to the focus tube ( you may have to rack the tube in or out a bit for this) adjust the secondary tilt until you can see the primary mirror clips in the secondary. They should all be visible and at the same distance from the edge of the secondary. The are some pics of how i should look on my website. I cant post a li k here but google astro baby collimation and you will find the article.

Step 3

With eye pressed to the focus tube adjust the primary mirror until the centre spot is where your pupil is. This step can be hard going and it will only be a best guess.

That will bring your mirrors to at least a rough collimation and the laser will take you the rest of the way. The alignment may no be perfect because only a sight tube can really set steps 1 and 2 accurately but this prcess should bring you pretty close.

Hope thats some help.