Help collimating my Skyliner 250px Dob

[BWBlackett]

Can someone help me with collimation. I've borrowed a baader laser.

I've managed to adjust the secondary mirror so the first bounce of the laser is hitting the circle marked in the centre of my primary.

The return is off centre in the laser target.

I can't figure out which knobs to turn on the bottom of my primary, they don't match what it says in the Skywatcher manual.

There are 3 sets of 2 screws, each pair has a smaller screw which would take a flat screwdriver and a larger screw with no slot. Any of the screws can be turned by hand.

I've messed with all of them and can get the laser to move around in a cicrle but not get anywhere near the centre mark on it's target.

Any help appreciated..... it's a clear night - I want to get outside !

Thanks,

Brian.

[Naz]

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

have a look at this, see if it helps. Clear skies :shock: what are they :x

naz

[Whippy]

Brian, what you've got are one set of three that actually mounts the primary onto the tube itself and the other three are for collimation. Which set are which I can't honestly remember. I'm pretty sure it tells you in the maunal, but again, I'm not 100%

Tony..

[BWBlackett]

The video is alright but it doesn't say which screws to what?

I have undone one of the large screws and it comes off - so it is on fact a nut - the thread must be attached to the mirror holder.

Does this mean that this is the locking screw rather than adjustment screw?

If I turn an adjustment screw too much is there a risk I can crack my primary ?

[BWBlackett]

Brian, what you've got are one set of three that actually mounts the primary onto the tube itself and the other three are for collimation. Which set are which I can't honestly remember. I'm pretty sure it tells you in the maunal, but again, I'm not 100%

Tony..

Tony, the manual doesn't look anything like the real scope!

It talks about a philips screw and a hex bolt for each pair - put actually they are a flat screw and nothing. Both have finger grips around the edges.

[BWBlackett]

Finally got it sorted - I think!

Had a great evening - perfectly clear skies.

M3, M92 (WOW), M103, M13, Double Cluster, M31 M32

Brian.

[jimlennie]

Brian, what you've got are one set of three that actually mounts the primary onto the tube itself and the other three are for collimation. Which set are which I can't honestly remember. I'm pretty sure it tells you in the maunal, but again, I'm not 100%

Tony..

Tony, the manual doesn't look anything like the real scope!

It talks about a philips screw and a hex bolt for each pair - put actually they are a flat screw and nothing. Both have finger grips around the edges.

Hi Brian,

The larger knob is for locking the mirror cell in place after collimation with the smaller slotted knobs. You should see the spot moving on your laser screen if you slowly turn the smaller screws. When I've done this ( only twice in the last 4 months ) I gently unseated all 3 large locking screws before adjusting the mirror. After successfully centering the beam on my laser, or spot in my cheshire I then tighten the locking knobs one at a time while viewing the laser return beam to make sure it doesn't move whilst locking. The ota was at an angle of approx 50 degrees while doing this and at outside temperature.

Hope this helps.

Jim

[BWBlackett]

Jim,

Thanks for the info, I don't think I've loosened then tightened the locking nuts - I will give that a go next time.

Brian.

[daz]

If you don't then you will stress the mirror and the views maybe warped.

Once you've done it once or twice, its fairly easy!

[philsail1]

Brian, take care when removing the screws/bolts at the mirror end of your telescope - I think the set that holds adjusts the mirror, have a small rubber washer between the outer casing and mirror - I think they are there to prevent one "cracking" the mirror. I removed the 8" mirror on my Skywatcher Newt some time ago (to gently clean the dust off) and found three rubber washers. (I had the devil of a job putting them back - had to use a dab of grease to hold them in place). Like "Whiplash," I can't rememberwhich bolts are which - but I see you've "sussed" it now. As "Jim" says, if you look at the laser collimator (or get someone to view the mirror) whilst you adjust one screw at a time, you should have seen some movement in the mirror. I felt tip marked the screws after the first time (but they are hidden behind the protective cover plate).

Regards,

Phil Edwards (philsail1)