Add guiding to a setup that already works unguided. Adding it to a setup that does not is how two problems become indistinguishable.
First, know your unguided limit
Find the exposure length at which stars stay round without guiding. That figure tells you how good the polar alignment is, and it is the baseline against which guiding is judged.
Mount the guide scope as rigidly as you can
Rigidity matters more here than optics. A guide scope that shifts relative to the main tube produces a real signal from a movement the main sensor never experienced, and the software will correct it in the wrong direction.
Start with gentle settings
A longer interval between corrections and a smaller correction each time. The loop should follow the mount’s slow errors, not the atmosphere’s fast ones.
Read the graph before the image
An oscillating trace means the loop is too aggressive. A slow one-way drift means polar alignment. A sudden step that does not come back means something moved mechanically, which is flexure or a cable pulling.
Then extend the exposure gradually
Double it, check the corners, double again. The point at which the stars stop being round tells you what to fix next, and it is rarely the guiding itself.
The questions that keep arriving
Do I need a guide scope or an off-axis guider?
A guide scope is simpler and cheaper and is fine at shorter focal lengths. An off-axis guider removes flexure entirely by picking light off the main optical path, and it becomes the better answer as focal length grows.
Why does more aggressive guiding make it worse?
Because the loop starts chasing atmospheric movement, which is faster than the mount can usefully respond to and essentially random. The corrections then add noise rather than removing it.
Last reviewed 17 September 2026