SUNSET: 
How to Align Your Newtonian Reflector Telescope
Accurate optical alignment is neither difficult, mysterious, nor time-consuming. In fact, it's only three steps away.
DIY: Astronomy Projects & Guidance
Offsetting Your Secondary Mirror
The secondary-mirror offset is no doubt the most misunderstood aspect of collimation. Luckily you don't need to understand it to collimate your instrument.
DIY: Astronomy Projects & Guidance
Collimation Tools
Three tools are commonly used to collimate Newtonian reflectors.