Archived posting to the Leica Users Group, 2008/04/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]On Apr 23, 2008, at 9:22 PM, Henning Wulff wrote: > At 6:37 PM -0700 4/23/08, Steve Barbour wrote: >> On Apr 23, 2008, at 5:42 PM, Tina Manley wrote: >> >>> At 08:33 PM 4/23/2008, you wrote: >>> >>>> so the coding has nothing to do with outcome or photo quality, just >>>> puts the lens into the exif...is that correct? >>>> >>>> >>>> Steve >>> >>> I read somewhere - I can't find it now - that the coding would >>> optimize the performance of the lens - addressing known vignetting >>> and color balance issue, particularly with wide angle lenses. >> >> >> rings a bell for me too Tina, but is this true ?! >> >> Somehow I wonder if it turned out to be speculation. >> >> >> Steve > > The coding provides vignetting correction for most lenses, but this > is of course more important for wide angle lenses. For lenses > shorter than 35, coding is definitely of benefit as it corrects for > the 'cyan corners' caused by the steep incoming angles of light > which causes 'frequency shifting' on lenses equipped with the UV/IR > cut filters. so it appears that the problem and therefore the coding benefit is seen with color, and only with UV/IR filters... Is this cited somewhere in Leica's technical support as I searched without success. Steve > > > The filters are interference filters, and do their job by the > interference of reflected radiation within the coating layers of the > objectionable wavelengths. When the angle gets steeper, the > incorrect wavelengths get cut; in this case the deeper red and not > just the IR wavelengths, therefore the cyan colour. > > If the camera knows the lens characteristics, it can do some pre- > processing on raw as well as jpeg files and counteract this > undesirable effect, and give consistent colour response across the > whole frame. The Wide Angle Tri-Elmar would be unusable with an IR/ > UV cut filter without such coding. > > The EXIF data on lens and focal length is just a side benefit of > this. Vignetting is also easy to correct in software if desired. > > I wouldn't bother sending perfectly functioning lenses in to get > coded if it weren't for this correction that the camera does. I have > a 28 Summicron where the cyan corners are just detectable, so I will > send in the lens at some point, but 35 and longer won't get sent in. > > -- > * Henning J. Wulff > /|\ Wulff Photography & Design > /###\ mailto:henningw@archiphoto.com > |[ ]| http://www.archiphoto.com > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information best, Steve "I never wanted to be famous" http://www.blurb.com/bookstore/detail/186890