A step-by-step guide on polar scope calibration

  • Before taking any action, please note that polar scope calibration (or registration) is a non-trivial task and is not required if your tracker performs normally within its load limit. This guide is intended for users who are familiar with the use of a polar scope and understand when calibration may be needed.

  • Also, please handle the reticle glass with care — it is fragile and may break if excessive force is applied. Damage caused by improper handling is not covered under the warranty.


This article is a detailed step-by-step guide on how to calibrate polar scope. 

First and foremost, reticle frames in polar scopes are made of a piece of glass or plastic and they are easy to break under stress. Caution must be taken to avoid crushing them when using Allen wrench to adjust the three set screws (the screws in red in Fig. 1) connecting reticle frame and polar scope body.

fig.1

Over tightening these screws is VERY likely to break the reticle frame. DO NOT GRAB THE PART OF THE WRENCH AT RIGHT ANGLE TO THE TURNING AXIS. Instead, always grab the axial part when tightening (Fig. 2). Stop tightening as soon as you feel resistance.

fig.2

Now let's go to the calibration part. The following steps assume you have a NOMAD star tracker, MSM polar scope and polar scope mount and an astro wedge. The phone mount adapter to NOMAD can work as polar scope holder too.

  1. Setup your wedge and MSM tracker with the Universal Mount on a tripod like you normally do (Fig. 3)

fig.3

 

  1. Adjust the hand knob (Fig. 4) on the polar scope mount so that polar scope can be rotated in the mount with ease and without wobbling. Rotating polar scope in the mount may cause scratch on its barrel. If this is a concern, you can wrap the barrel with transparent tape.

💡 Pro Tip for Maximum Precision: If you find it difficult to eliminate wobbling due to the round base, use PTFE (Plumbing) tape instead of standard tape. This creates a low-friction, "snug" fit that keeps the scope perfectly centered while allowing you to rotate it effortlessly during calibration.

fig.4

  1. Choose a feature on the polar scope as your reference point, for example, one of two circled features in Fig. 5 would serve as a good reference to memorize. The reference will help you tell whether the scope has been turned 180 degrees later on.

fig.5

  1. Rotate the scope so that the feature you chose is facing upward to the sky.

  2. Find any pointed ourdoor target that is more than 100 meters away. Corner of a building is a great choice (Fig. 6). It's sharp and easy to find.

fig.6

  1. Adjust the wedge so that the center of crosshair is aligned to the target(Fig. 7). The building is upside down due to polar scope imaging principle. You may need to focus your polar scope in this step.

fig.7


  1. Rotate the polar scope by 180 degrees. You can tell by checking if the reference feature you chose in 'step 5' is now facing downward to the ground.

  2. For an uncalibrated polar scope you will notice the center of crosshair is off from target (Fig. 8). Now imagine a virtual line connecting the center of crosshair and target. The axis of rotation of the polar scope is now sitting at the mid point between the target and center of crosshair (Fig. 9) That is the point we want to move the center of crosshair to.

fig.8
fig.9

  1. Mentally memorize the red point (Fig. 9) position relative to the reticle pattern. It's hard, but try your best anyway.


  1. Adjust the wedge so that the target reaches the red point (Fig. 10).

fig.10

  1. Tighten the hand knob on Universal mount to prevent any accidental rotation of the polar scope.


  1. Now our target is at the center of rotation of polar scope. It serves as a good visual reference. All there left is to adjust the three set screws to move the center of crosshair to the target (Fig. 11). If you were to loosen one slightly and tighten one down, it will shift the reticle up, down, left, or right. It's a trial and error thing. Be patient and you will finally get it there. It's important to note during this adjustment not to loosen the set screws too much. A quarter of a turn at most on each screw at a time.

fig.11

  1. Repeat step 6 to step 12 if needed. A calibrated polar scope looks like Fig. 12 where center of crosshair stays on target when the scope is rotated on its axis.

May 7, 2026

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