Enter your telescope's aperture and focal length, an eyepiece and an optional Barlow lens. The calculator shows:
- Magnification and the useful range for the aperture.
- Exit pupil - whether the view will be bright, comfortable or too dim.
- True field of view, also in Moon widths, so you know what fits in the eyepiece.
- Resolution (Dawes limit) and the approximate faintest star visible under a dark sky.
It warns when a combination goes past what the telescope or the air can deliver.