where do you put cross hairs in convex lenses? and...why can't you put them in concave lenses?
2007-09-25 15:53:43 · 3 answers · asked by Anonymous in Science & Mathematics ➔ Astronomy & Space
The crosshairs have to be at the focal plane of the eyepiece to appear sharp when you look through the instrument. In a commercial eyepiece that means at the field stop. You can't use them with a negative (concave) lens because there is no real focal plane. In a compound eyepiece, if the field lens is negative the focal plane is somewhere inside and that usually won't work either.
2007-09-25 17:54:03 · answer #1 · answered by injanier 7 · 0⤊ 0⤋
Depends on what you need the cross hairs for. In most cases there are two, perpendicular to each other, crossing at the center of the lens. Convex lenses, since it makes images smaller and viewing area larger, is used for targeting. Concave lenses doesn't serve any purpose as far as targeting is concerned. It is mainly used for magnification. No purpose is served by putting cross hairs on it. You can if you want but it is uselsss.
2007-09-25 23:34:11 · answer #2 · answered by worldneverchanges 7 · 0⤊ 0⤋
Hi. I think in all cases the cross hairs have to be at the focal plane.
2007-09-26 00:02:53 · answer #3 · answered by Cirric 7 · 0⤊ 0⤋