Starguide - A Practical Guide to Astro-Photography

Actual Step

Step 4a: Primary Mirror Collimation using TS RCOLLI

updated: 2024-05-08

Purpose

Aligning the primary mirror with the optical axis of the telescope

Previous Step

Step 2a: Collimation of the Secondary Mirror

Next Step

3 alternative follow-up steps:

1. Step 2: Re-check and correct mirror distance
2. Step 3a: 2nd mirror collimation using a TSRKOLLI Collimator
3. Step 5: Final Collimation 

Preparation

Place the optical tube on a table or move the telescope on the mount into a horizontal position. It is helpful to aim the telescope at a homogeneous bright surface (paper, house wall, ...). Now put the collimator into the 2" receptacle of your focuser. It helps when you orient the labeling to the collimation screws, this makes working easier. Press your hand slightly from the backside against the collimator. Now you are ensured that the collimator is optimally placed in the focuser. 

• If possible remove the internal baffle on the main mirror that blocks obliquely incident light (this is possible e.g. on the TSO 203/1624 RC PRO)
• Slightly untighten den locking screws on the backside of the mirror using a 2.5mm Allen key
• Next, switch on the collimator in Newtonian/reflector mode (red LEDs)

• Instead of using the TS RCKOLLI I used a small Nikon S9900 - the lens tube fits exactly into a 2" receptacle 
• WARNING: ensure, that the camera doesn't shut down during the process as it will try to retract the lens tube and therefore might drop off the focuser!)

Misaligned Primary Mirror

• looking though the hole of the TS RCKOLLI
• Here you can see a misaligned primary mirror, this is shown by the unequally wide outer white border.

Misaligned Primary Mirror

• photo shot with the Nikon S9900 setup (above)

Well Aligned Primary Mirror

• Now you center the outer ring by adjusting the primary mirror using a 3 mm Allen keys on the silver push/pull screws.
• The result at the end of this second and last step of the collimation should look like this. Collimation is finished and the telescope is ready for the night.
• 
  

Well Aligned Primary Mirror

• photo shot with the Nikon S9900 setup (above)

Finalization

• Re tighten the locking screws slightly to prevents that the pressure on the cell gets too strong or that the mirror position remains unstable.
• Re-install the internal baffle on the main mirror.

Next Steps

3 alternative follow-up steps:

1. Step 2: Re-check and correct mirror distance

1. Step 3a: 2nd mirror collimation using a TSRKOLLI Collimator
2. Step 5: Final Collimation