Archived posting to the Leica Users Group, 2007/10/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]"Problem" or "characteristic"? Perhaps another way of looking at it is that the 28mm Summicron vignettes in the IR spectrum, and you are exposing for the outer field rather than the center, leaving the center overexposed. That raises an interestig question -- does vignetting vary according to the color or spectrum of the light? Too bad Erwin is not here for such Q's! Tom On Oct 12, 2007, at 2:10 PM, Leonard Taupier wrote: > George, et al. > > I've verified a problem with the 28mm Summicron on an M8 and IR > filter when trying to take Infra Red photos. > > There is a hot spot present in the center of the frame when trying > to take IR photos with the above setup. The problem looks like > flare, a circle of low contrast in the center of the frame. The > problem is most noticeable at the smaller lens openings where the > hot spot is clearly defined. As the lens is opened up the hot spot > becomes larger and less pronounced but the center area is still > lower contrast. I did not see this at f2 and f2.8. Here is a photo > taken at f16. > > <http://gallery.leica-users.org/v/LeonardT/Infra_Red/ > 28mmSummicronIR.jpg.html> > or > http://tinyurl.com/yreo78 > > I used two M8 cameras for the test. All photos were taken on a > tripod with the sun directly behind the camera and shaded by my > body. The filter was a Hoya R72. A lens hood was on the lens. The > problem showed up with both M8 cameras. > > The same test was also performed using the 28mm f2.8 Elmarit (non- > asph), 35mm Summicron asph, 24mm Elmarit asph and the 21mm Elmarit > asph. Only the 28mm Summicron asph showed the hot spot problem. > > The problem does not show up when using a Red R60 filter. > > Len > > > > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information