Archived posting to the Leica Users Group, 2009/12/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hey! Watch out there!! That's seeming to make sense... Stop it! ric On Dec 7, 2009, at 5:46 PM, wildlightphoto at earthlink.net wrote: > Focus shift is caused by spherical aberation. Less spherical aberation = > less focus shift. Spherical aberation is seen as different planes of focus > for light rays from different regions of the lens, i.e., central or outer > regions. > > With spherical aberation, at the widest apertures there's never a precise > focus 'plane', it's more like a zone of reasonably good focus: a blending > of the central and outer rays' focus planes. When the lens is stopped down > the influence of the outer light rays is removed so the zone of good focus > becomes more sharply defined and since it's influenced more by the central > light rays, it shifts toward the the central light rays' plane of focus.