How I can add my binoculars

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Q: My binos are 20x90 but they seem to be 18.5x85 
from what i see online so 90mm main lens (85mm inside due to baffles) 
20x magnification (18.5x due to smaller lens?) exit pupil is around 4mm
FoV is 3deg and of course this company was bought out and full specs no longer exist...

A: The 3 deg FOV is actually all you need to setup the proper FOV ring for your binos in DSO Planner, but you need a bit of math and optics knowledge. Here is how I setup mine:

Knowing that TFOV = Eyepiece AFOV / Magnification and that Magnification = Objective Focal length / Eyepiece Focal length,

  1. Go to the Settings / Astro Equipment / Telescopes database.
  2. Use the "Add new instrument" button at the bottom to open Instrument parameters dialog.
  3. Give your bino a name, e.g. "Bino 85".
  4. Set the "Aperture" to 85 mm and the "Focal length" to 85 mm too, just to save your memory from remembering more than one number (85).
  5. Save.
  6. Long tap the new "Bino 85" record's line on the "Optical instruments" list.
  7. Select "Assign eyepieces" from the pop-up menu. That will open the Eyepieces database.
  8. Use the "Add new Eyepiece" button at the bottom and select "Eyepiece" to open the Eyepiece parameters dialog.
  9. Give it the same name for clarity "Bino 85".
  10. Enter "Focal length" 85 mm (so we have the magnification equal 1, don't worry that will affect nothing but simplifies all the math as that will provide the Magnification = 1 ).
  11. and finally AFOV = 3 deg, as stated for your binos.
  12. Save.
  13. Make sure you have that new EP assigned (having the check mark on the right).


If you will later find out that the actual TFOV of your binos is more or less than 3 deg exactly, just open the Eyepieces database again, long tap that "Bino 85" eyepiece line, select "Edit" from the pop-up menu, and change 3 deg AFOV to whatever you believe it actually is.