Secondary Mirror Allignment.

[woodmeister]

Hi, I have a question on aligning my secondary. When centring my secondary mirror in the centre of the tube, I use a ruler to measure the distance between the edge of the tube and the centre of the secondary mirror holder. However when all the lengths match up and I then look under my focuser my secondary is not in the centre of the view and needs pulling down quite a bit. I have tried just centring by looking down the focuser and then moving the mirror until it appears centre.

My question is which would be the best way to go about it? just match up the spider vane lengths. Or ignore the lengths and adjust by eye?

Could the problem be elsewhere? for example focuser slop or focuser placement / alignment?

[Charic]

Sounds normal! What brand of scope do you have?

The  centre bolt on the Spider assembly   needs to be centred in the OTA then the mirror itself needs to be circular and concentric to the focuser tube.

Have you any reference to this guide? http://www.astro-baby.com/collimation/astro%20babys%20collimation%20guide.htm

Its a  standard for advice on collimation.

[brantuk]

+1 for Astrobaby's guide

[Jason D]

My question is which would be the best way to go about it? just match up the spider vane lengths. Or ignore the lengths and adjust by eye?

Answer is simple. Adjust by eye.

Collimation is about aligning optics. It is not about mechanical alignment. There is nothing significant about the the OTA or vane lengths for collimation. The OTA can have an irregular shape yet perfect collimation can be achieved as long as the OTA does not get in the light path.

Jason

[woodmeister]

Cheers for the advice. I have used astro baby's guide before, Was not sure as the guide said use the measurements from edge to centre yet secondary was not centred. Thanks for clearing this up as it was usually on the back of my mind.

This noob appreciates the advice given. Clear skies to you.