Tag Archives: lens

John Herschel and his Lens Designs

by John Church Charles Hastings once wrote that the lens which is now on our Hastings-Byrne refractor was similar in design to the types described by John Herschel (1792-1871). He also mentioned that such lenses do not greatly differ from … Continue reading

Posted in April 2021, Sidereal Times | Tagged , , | Leave a comment

Geometrical Optics and the Hastings-Byrne Refractor: Part II

John Church Last month I reviewed the “lens-maker’s formula” that allows one to calculate the focal length (the inverse of the “power”) of a thin lens, provided that one knows the refractive index of the glass and the radii of … Continue reading

Posted in April 2012 | Tagged , , , , | 1 Comment