Archived posting to the Leica Users Group, 2007/10/12

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Subject: [Leica] George: 28mm Summicron IR problem
From: jhnichols at bellsouth.net (Jim Nichols)
Date: Fri Oct 12 15:45:16 2007
References: <7FA6647D-A36C-4A86-84B3-A4756DA8FB77@comcast.net> <673C7DEC-A9C1-490A-8F6F-821246CF27FC@comcast.net>

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
> 



Replies: Reply from imagist3 at mac.com (Lottermoser George) ([Leica] George: 28mm Summicron IR problem)
In reply to: Message from len-1 at comcast.net (Leonard Taupier) ([Leica] George: 28mm Summicron IR problem)
Message from tomschofield at comcast.net (Tom Schofield) ([Leica] George: 28mm Summicron IR problem)