Using a Digital Finder with ScopeDog

Another Covid lockdown projct was the development of a digital finder for my 18”. I call it an ‘eFinder’.

It is fully described here.

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Here’s a photo of it installed on my 18” Dobsonian.

Basically it is a very fast imager with a 1 degree field of view. Images are plate solved to determine the precise pointing of the eFinder.

The eFinder can be mechanically aligned to the main telescope optical axis, or there is a calibration routine that measures the alignment error and subsequently applies it to displayed results.

This the eFinder is effectively determining where the main scope is pointing, to better than 1 arc minute.

I can use this in various ways.

  • Refine Goto’s. The ScopeDog drive typically gets me within 10 arc mins of the target. The errors are down to initial Nexus DSC alignment and the stability and orthogonality of my scope mount.
    The eFinder can automatically finish the goto by sending ScopeDog commands to close out any error.
  • Make initial two star alignments easier. Instead of aligning on Names Stars in the Nexus catalogue, I can just point my scope at a convenient part of the sky and the eFinder will determine the position very accurately and send the result to the Nexus DSC as a pseudo alignment ‘star’.
  • Auto track. For targets near the horizon (refraction effects), or in other cases where accurate encoder portions are not being obtained. The eFinder can continuously cycle through image-solve-movescope at about one cycle every 5 seconds.
  • The eFinder can display a simple red LED pointing ‘error’ display, or the image that has been captiured and solved. This image can have the eyepiece field of view and orientation superimposed, along with say ngc objects annotated. very handy to help identify what is in the main scope eyepiece.

The eFinder communicates with the ScopeDog via the Nexus DSC USB port.

© AstroKeith 2022