Collimating Newtonian & SCT telescopes

To ensure the  best possible performance of a telescope the optics need to be properly aligned or collimated. Adjusting the main and secondary mirrors is a simple operation that should be checked and carried out regularly.
The adjustment is usually carried out in two steps.
1. Preliminary adjustment is completed during day light.
2. Precision adjustment, is completed at night on a star.

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1. Preliminary adjustment

looking through a telescope focuser with the eyepiece removed the secondary mirror can be seen reflected in the main mirror at the bottom of the tube telescope tube fig 1. With the eye centred in the focuser this is how a correctly collimated telescope looks 

Fig 1

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Fig 2 shows a telescope badly out of collimation 

Fig 2