Observational Tools

Calculate Scope Characteristics
Aperture (mm):
Focal ratio:
Focal length (mm):
Dawes limit (arc-secs):
Approx limiting visual mag:



Calculate Focal Reducer's acting focal ratio
Focal reducer's focal length (mm):
Backfocus (mm)::
Acting focal ratio:
The published focal ratio of any focal reducer is only achieved if exactly the correct backfocus (the distance from the focal reducer to the camera's or CCD's image plane) is achieved. Any variation in the actual backfocus will change the acting focal ratio and possibly comprimise the focal reducer's performance. To calculate the focal reducers acting focal ratio its focal length must be known.
Telescope focal ratio:
Acting focal length (mm):
Telescope aperture (mm):



Calculate Imaging Field Of View
Sensor size (X by Y in pixels):
Sensor pixel size (X by Y in microns):
Scope focal length (mm):
Fov in arc mins:
Arc secs / pixel:
Bin:
Reducer:
Acting focal length (mm):
OR aperture (mm):
and focal ratio




I have put all of the code as javascript functions embedded in the HTML so that it is viewable, if you are interested in the algorithms and code to implement these calculators try right mouse click->view source in your browser.


© Keith Ehren 2025.