Guiding Ratio
Match the guider to the imaging train.
Compare the angular scale of the main camera with the guide camera and see the centroid precision needed to hold an imaging pixel.
Purpose and method
What this calculator does
Is my guide setup sufficiently precise? Compare guide-camera and imaging-camera angular scales.
In words: Guiding ratio compares angular sampling in the guide and imaging systems.
The main imaging scale comes from the saved telescope, modifier, camera and binning. Guide-scope and guide-camera measurements remain local because they are not part of the equipment profile.
Working geometry
Imaging and guiding scales
Two optical systems sample the same tracking motion at different angular scales.
Inputs
Two optical paths
Main imaging train
Guide train
Calculated now
Scale and demand
- Imaging scale
- 0.776″ / px
- Guide scale
- 3.223″ / px
- Guide : imaging ratio
- 4.16 : 1angular scale per pixel
- Half-pixel demand
- 0.120 guide px0.388″ on sky
Equations
A guide star centroid can be measured to a fraction of a guide pixel, so the ratio alone is not a pass/fail rule.
Guide-star signal, seeing, exposure time, mount response, flexure, calibration and software settings often matter more than a single ratio. An off-axis guider can also avoid differential flexure.