[mental4astro (Alexander)]

Like many enthusiastic amateurs, I bought a GSO laser collimator. What I didn't know was that this little devise lacked a bit of collimation itself.

No matter how carefully I went through the collimation process, a tiny comet tail remained on the brightest of stars. Was there something wrong with my scope? But this same "tail" appeared in another Newtonian I have too.

The other week, I used a mate's GSO collimator. The beam on this one was the size of a 5cent piece! Though mine was slightly ovoid in shape, this one was way too big.

As I don't want to spend over $250 on a you-beaut one, I looked into how to pimp this one to perform better.

As it turns out, it's EASY!

Tightening the beam requires nothing more than a 10mm X 10mm bit of masking tape and a sharp pencil.

Tightening the beam:

* With a suitable hex key, remove the screw holding the frosted diagonal (pic. 1)
* Place the bit of tape over the hole that sits closest to the laser
* Shining a light through the diagonal so you can see the illuminated hole shining through the tape, use your pencil to pierce the tape right in the centre. Make the hole the same size as the diameter of the lead, about 2mm. Any smaller and the diffraction pattern that results makes the beam to big and useless (pic. 2)
* Replace the diagonal into the collimator

Collimating the laser:

* Hammer four 50mm nails into a block of wood to form two V-shaped cradles for the collimator to sit in (pic. 3)
* Number the three collimating screws on the laser, so you know which one you've tweeked
* With the laser in the cradle, and the cradle clamped in place so it doesn't move, shine the laser onto a card at least 3m away - turn the laser in its cradle, if the beam stays in the one spot, it's collimated, if it traces a circle pattern, it needs collimation
* Do quarter turns to trace the pattern, then tweek the collimation screws and seek to make the beam stop tracing the pattern

The final picture shows the pattern my laser traced initially and as I tweeked it until it stayed bany in the middle. My laser was 4.8m from the card, and the angle of deviation was 0.18degrees - Bugger all, but this was making all the difference.

The only other thing I had to do to make sure of the best collimation for my big dob was mark a tiny centre spot on the secondary mirror with a permanent marker (off-setting needs to be taken into account). The laser is aimed at this spot. This will also show if the secondary needs to be raised or lowered, or if the focuser is not square with the secondary.

Clear skies,

Mental.