[Leica] George: 28mm Summicron IR problem

[grduprey at mchsi.com (grduprey@mchsi.com)]

Len,

Have you tried a different brand of IR filter?  Don't have the summicron, 
but my 28 Elmarit Asph does not show this.  I have the Heliopan ir filter on 
it.  Don't know if changing the filter will make any difference, but worth a 
try.

gene

-------------- Original message from Leonard Taupier <len-1@comcast.net>: 
-------------- 


> 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. 
> 
> > 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 
> 
> 
> 
> 
> 
> 
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