Archived posting to the Leica Users Group, 2007/10/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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. Jim Nichols Tullahoma, TN USA ----- Original Message ----- From: "Tom Schofield" <tomschofield@comcast.net> To: "Leica Users Group" <lug@leica-users.org> Sent: Friday, October 12, 2007 5:34 PM Subject: Re: [Leica] George: 28mm Summicron IR problem > "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 > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information >