[Leica] George: 28mm Summicron IR problem

[len-1 at comcast.net (Leonard Taupier)]

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