[email protected] wrote: > If there's any truth in that, then it's nothing to do with the basic optics > of how light passes through a plano-convex lens. A converging lens is a > converging lens in both directions.
Further to what I wrote, I think I might have got to the bottom of it... Whilst the basic principle above is fundamentally true - a plano-convex lens converges light, whichever way round it is mounted - there is a difference in terms of the abberrations. No lens focuses light perfectly: there will be second-order effects such as spherical abberation (light rays passing near the edge of the lens aren't quite in focus with those passing near the centre) and chromatic aberration (different colours bend different amounts and therefore focus at different distances). In the case of a plano-convex lens, spherical aberration is more pronounced when the light passes from the flat side. It will still bend all the light inwards towards the centre, but the increased amount of aberration means that quite possibly it won't focus it sharply enough to start a fire. Whether this also explains Bruce's experience that it diffuses through the cabin better, I haven't worked out yet. See http://folk.uio.no/walmann/Publications/Master/node8.html for some diagrams. Martin L
