Archived posting to the Leica Users Group, 1999/08/27
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]> Date: Fri, 27 Aug 1999 12:07:31 -0400 > From: "Dan Post" <dwpost@email.msn.com> > Subject: Re: [Leica] BOKEH of 35mm lenses (prev.Reply to visitors > ofmywebsite / Leica M comments) > > Mikirosan- > Interesting post, that. I was wondering- and this goes back to my days when > I studied the psychology of perception, that those lenses that have the same > type of abberations as might be found in the human eye, might have the best > 'perceived' bokeh? > Do we have any optometrist out there that have studied the human eye lens as > an image forming system? Does the brain 'correct' certain abberations, and > lenes that render images similar to those 'corrected' by the occipital lobe > appear more natural and pleasing? There might be a thesis in this! > We use biology to design ergonomic machines all the time, and I was > wondering if anyone has thought about designing a lenses that 'sees' similar > to the way we 'see'- not just with the eyes, but with the brain's input as > well. > Dan Dan, You asked if an optometrist LUG member could contribute an answer. I'm an ophthalmologist and while I cannot answer all of your questions regarding the brain's correction of optical aberrations, perhaps I can give a partial answer. First off, the human cornea is naturally aspheric. Unfortunately it doesn't remain so after many types of refractive surgery using today's lasers - the software changes them to spherical shapes that generate more chromatic aberrations. In fact, corneas that have undergone excimer laser surgery have more distortion if the photo-ablated area is not properly centered on the optical axis (this distortion is also affected by the pupil size). By extrapolation, I would assume that an aspheric camera lens would show less distortions with less aperture dependence. Now whether distortions are what adds to one's bokeh I don't know. (Using a different perceptual analogy, the human ear hears sounds with even order harmonics distortions like tube amplifiers generate, which is possibly one reason why solid state amplifiers that generate odd order harmonics sound less smooth or lush than a tubed amplifier.) As for brain processing, I don't think the brain corrects for any optical distortions. It does process spatial information, such as depth and size relationships, but I don't know of any particular 'circuitry' that minimizes optical problems. As an example, there are various artists whom we now know had various types of eye diseases ranging from severe astigmatism to media opacities (cataracts, scarred corneas) who simply incorporated these distortions into their art. One such theory is that El Greco's tall graceful figures were due to his severe astigmatism and was not obviously corrected by his brain (which apparently thought they looked OK). Bob Jones rjones4@home.com