Archived posting to the Leica Users Group, 2002/01/31
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 06:16 AM 31/01/02 -0800, you wrote: > > From: "Joseph Codispoti" <joecodi@clearsightusa.com> > > > > There has not been a Leica thread in a while. > > Some time ago a member asked what "microcontrast" is. No one responded (at > > least I don't recall a reply), I wanted to respond but, like the > inquirer, I > > don't have the faintest idea what microcontrast stands for. > > So let me ask the same question, what is microcontrast? Following sescription found at http://www.imx.nl/photosite/leica/mseries/testm/M10-50.html Overall contrast. Macro contrast is the difference between the deepest black and the lightest highlight of a scene, that the lens is able to record faithfully. An ideal lens would only transmit all the light from the subject and bring it to sharp focus in the focal plane. In real life a quantity of non-imaging forming light ( for instance reflections between surfaces of two lens elements) will spread uniformly over the whole negative area. When we are taking pictures of a scene that has deep shadows, the light energy hitting the emulsion can be so low that no latent image will be formed. After development this negative area will be transparant. A lens with a high flare factor however will 'illuminate' the shadow areas and after development the negative will now have a certain density, but of course no details of the subject will be recorded. When comparing two lenses with the same nominal aperture (say f/1,4) we might think that the one that gives a slightly higher shadow density is actually a bit 'faster' as more light seems to be transmitted. In fact this lens may be just more flare prone and the other one could be more highly corrected for optical aberrations. Micro contrast. Microcontrast refers to the relative luminances of two adjacent very small subject areas. It has special relevance to very fine textural details. If some object detail is just recorded, but the contrast is below the visual threshold, we are not able to see it. What we will see however is a kind of image noise, that reduces the clarity of the picture. It will be appreciated that good microcontrast is needed when the higher spatial frequencies must be clearly separated. Flare eradicates marginally resolved textural details. - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html