Actual Step

Step 1: Correct the Focuser Tilt

updated: 2024-05-14


SCTs (Schmidt-Cassegrain) or RCTs (Ritchey-Chr├ętien) telescopes may have a third collimation possibility: the tilt of the focuser. This can be compensated with a tilting adapter flange that serves to compensate a minimally skewed position of the sensor or a slight tilt of the focuser. 

Whether or not the focuser is tilted depends heavily on the design of the focuser. Some focusers guarantee a clean alignment of the optical axis even when pulled out. Therefore, alignment of the focuser is not absolutely and always required.

The aim of this step is to get the plane of the camera sensor parallel and centered to the secondary mirror (or to align the optical axes of the focuser and the telescope tube).

Required HW

Previous Step

Checking the Collimation

Next Step

Step 2: Check and correct Mirror Spacing

Many telescopes have a third collimation possibility - a tilted focuser. It is often tried to compensate a bad collimation with this tilting, but that does not work well. For this reason, you should adjust the tilting mechanism until it reaches the position stop before collimation. Thus it is ensured that the optics is optimally adjusted to the focuser.

A tilting mechanism like an Tilting Adapter Flange should be used for adapting the camera sensor optimally to the telescope. Thus you can compensate a minimally skewed position of the sensor or a slight tilt of the focuser. Insert the Tilting Adapter Flange between an extension tube and the focuser.

Correcting the Focuser Tilt on Standard Closed Tube RCTs (like TSO 203/1624 RC PRO) using a Cheshire Device


Insert a Laser Collimator (Cheshire or similar device) like the Svbony Laser Collimator into the rear end of the focuser and watch where the red laser spot hits the secondary mirror (this is a bit difficult to observe in closed tube telescope like the TSO 203/1624 RC PRO).

Loosen the corresponding locking screws and use the adjustment screws to move the red laser dot to the center of the secondary mirror ring.

Don't forget to fix the locking screws again after this step.

Correcting the Focuser Tilt on an Open Tube telescope Using a Laser Collimator

Misaligned Focuser

Note: This procedure applies only to open-tube telescopes that allow a side view of the secondary mirror, such as:

Initial situation:

  • the laser does not point exactly to the center of the secondary mirror

Alignment Steps

  • Insert the laser collimator into the 2" receptable and pinch it tight only slightly to make sure the laser collimator sits right in the middle of the focuser.
  • Turn on the laser
  • watch the laser point on the secondary 
  • slightly loosen the locking screws on the tilting adapter flange
  • turn the adjusting screws on the adapter to move the laser point to the center of the secondary mirror

Next Step

Step 2: Check and correct Mirror Spacing


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