Telescope Eyepiece & Camera Calculator cover

Which eyepiece for what, and what your camera will see.

You have four eyepieces and a Barlow and you still reach for the same two. This tells you what each one is actually for on your scope, what is missing, and which one to put in for the thing you are pointing at.

WHAT IT DOES

  • Magnification, exit pupil and true field for every eyepiece, with and without the Barlow
  • Useful range for your aperture and your eyes (max pupil by age), Dawes limit, limiting magnitude
  • Verdicts: low, medium, high, very high, empty magnification, wasted aperture
  • Gap finder: exit-pupil bands with nothing in them, and the eyepiece focal length (mm = exit pupil × f-ratio) that fills each
  • Fourteen targets (Moon, Jupiter, Saturn, Mars, two doubles, M42, M45, M31, Double Cluster, M13, M51, M57, M27) matched to the best eyepiece with the reason
  • Camera: nine sensor presets (ZWO, DSLR, full frame), reducers and Barlows, image scale in arcseconds per pixel, field, sampling against your seeing, planetary f-ratio, NPF untracked exposure by declination

Who it's for

Visual observers deciding what to buy next, and anyone putting a camera on the back for the first time.

What you get

  • The calculator (one .html file, runs in any browser, offline; works on a phone at the eyepiece)
  • A 2-page quick-start guide

Good to know

  • One file. No install, no account, no subscription, no internet needed after download.
  • Your data stays on your computer. Export a backup any time; import it on another machine.
  • Works on Mac, Windows, Linux and iPad (open the file in Safari or Chrome).
  • Instant download.

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Telescope Eyepiece & Camera Calculator

power, exit pupil and true field for every eyepiece, which one frames each target, the gaps to buy, and camera sampling

Aperture and focal length in. Every eyepiece (with or without the Barlow) gets magnification, exit pupil and true field and a verdict; fourteen targets from the Moon to M31 get the eyepiece that frames them best; the exit-pupil bands with nothing in them get a focal length to shop for. Switch to the camera and it gives image scale, field, sampling against your seeing, the planetary f-ratio, and the longest untracked exposure.

Pay with card, Apple Pay and more. Download right after.

One-time price in US dollars, checkout by Stripe. After paying you land on a page with your download link. Each link works for 15 minutes, and reopening that page makes fresh ones.

  • Telescope-Eyepiece-Calculator.zip