Archived posting to the Leica Users Group, 2007/10/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Here is an interesting artifact from the early Canon 18-55mm. It is said the new one (II) is more resistant to such optical bravura. http://www.laweekly.com/news/news/jimmys-final-gasps/632/ s.d. On Oct 12, 2007, at 5:51 PM, Leonard Taupier wrote: > > 3. IR and Lenses > > > In addition to the sensitivity of the sensor the quality of digtal > infrared depends on the characteristic of the lens. > > For example, the Canon EF-S 18-55mm f/3.5-5.6 typically produces a > pronounced hot spot as can be seen in the sample picture to the > left. The hot spot is a a result of internal reflections within the > lens produced by the lens' coatings. Some types of coating are not > transparent to near-infrared wavelengths. > > > > The above was taken from a web site dedicated to Infra Red digital > photography. Quite a few lenses are listed which produce these hot > spots. The author did not include Leica lenses in the recommended > or hot spot producing lists. > > Len > > > > > > On Oct 12, 2007, at 6:59 PM, Lottermoser George wrote: > >> Having attempted to deal with these "hot spotted" images in a >> number of different ways; I think it would be a poor use of time >> to attempt to correct it with blocking in the optical path. >> >> For a brief period I considered the possible use of a center >> weighted filter. But once you see how "hard" this hot spot is; and >> without contrast; it becomes fairly evident that any available >> center filter would not work. You'd have to go through mind >> numbing tests; looking at all sorts of various "donut" >> configurations in the image to come anywhere close to a "block" >> correction. And even if you could get there and correct for the >> "over exposure" you'd still have to deal with the lack of contrast >> in that "spot." >> >> Regards, >> George Lottermoser >> george@imagist.com >> >> >> >> On Oct 12, 2007, at 5:45 PM, Jim Nichols wrote: >> >>> I've been following this thread, but since I have none of the >>> equipment involved, haven't said anything. In looking at Tom's >>> comment, it occurred to me that it might be interesting to try a >>> blocking center spot applied to the filter, similar to the >>> approach used with one of the early Leica lenses. >> >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information