Archived posting to the Leica Users Group, 2006/11/15

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Subject: [Leica] Some IR filtration experiments
From: davison_m at msn.com (MARK DAVISON)
Date: Wed Nov 15 13:57:27 2006

Leonard,

I didn't notice any light loss with the IR cut filter (the Tiffen hot-mirror 
filter).  These filters are listed in the manufacturers catalogs as having a 
filter factor of 1.

Mark



>From: Leonard Taupier <len-1@comcast.net>
>Reply-To: Leica Users Group <lug@leica-users.org>
>To: Leica Users Group <lug@leica-users.org>
>Subject: Re: [Leica] Some IR filtration experiments
>Date: Wed, 15 Nov 2006 16:25:37 -0500
>
>Mark,
>
>Great work. Your results are especially interesting to me as I want  the 
>kind of sensitivity to IR that the M8 has. I shoot a lot of IR  photos. 
>That's just the opposite of everybody else. I'm very familiar  with the IR 
>sensitivity of the D200 (none), the D2H (little more than  average), D2X (a 
>little less than the D2H), and D1X ( more sensitive  than the D2H). The hot 
>mirror IR filter approach may be fine in the  short term but that's slowing 
>down all your lenses by 1 to 2 stops.  Since your experiment with the Phase 
>One profile has only limited  success, you're right. Leica will have to fix 
>it. That may not be too  easy as Leica has already suggested that adding an 
>IR filter over the  sensor may (my interpretation) mess up their edge 
>performance they  went so hard to develop). Your new Heliopan filter 
>experiment will be  interesting but I think the UV contribution to the 
>problem is very  minor compared to IR. Most modern lenses roll off UV 
>fairly well.  I  have to use enlarging lenses for UV images. And your D200 
>also has  absolutely no sensitivity to UV. It looks like a winner right 
>now.  While I want the IR sensitivity of the M8, not at the expense of  
>color cast problems. For now I'll just wait and see how the M8  evolves and 
>continue to buy more film for my M6 and M7s.
>
>Thanks and keep us informed on your future experiments.
>Len
>
>
>On Nov 15, 2006, at 1:45 PM, MARK DAVISON wrote:
>
>>I have been conducting some experiments to understand the issue of  IR 
>>contamination and filtration in digital cameras.  I have posted  some 
>>results at
>>
>>http://gallery.leica-users.org/v/MarkEDavison/M8infrared/
>>
>>to show some comparative examples of IR filtration.  I have  included a 
>>Leica M8 shot where the filtration was done by applying  a modified Phase 
>>One profile which is supposed to correct blacks  under tungsten light. My 
>>conclusion is that the software filtration  works surprising well on the 
>>blacks that are IR contaminated, but  hardly affects the other 
>>contaminated colors at all, but you should  look and come to your own 
>>conclusion.
>>
>>(Note: this is a cross post.  There is an on-going discussion of  software 
>>profile methods for IR filtration at
>>http://www.leica-camera-user.com/digital-forum/9178-magenta-work- 
>>around-capture-one-workflow.html
>>
>>or
>>
>>http://tinyurl.com/y6cjx2
>>
>>which gives more detail on the origins of the modified profile I  used on 
>>the Leica M8 image.)
>>
>>Here's a description of the shots:
>>
>>The scene was shot with incandescent illumination from ordinary  
>>lightbulbs. The camera white balances were set to 2800 K  except  for the 
>>Epson R-D1, which was set to incandescent. (The Epson R-D1  does not allow 
>>you to set white balance in Kelvin.)
>>
>>The first example is the D200, which is very insensitive to IR. The  
>>colors in the first D200 photograph are a very accurate rendition  of the 
>>way the scene appears to my eye. Take special note of the  maroon and 
>>green pile blankets, the black Leica M lens, and the  black pile jacket at 
>>the bottom of the photograph. The second  photograph shows the D200 with 
>>IR cut filtration (via a Tiffen  standard hot mirror filter). There is 
>>hardly any visible change in  the colors. The third photograph is with the 
>>D200 and the IR pass  filter (a Hoya R72), taken at the same exposure as 
>>the first two  photographs. There is no visble IR at all at this exposure.
>>
>>The photographs continue in sequence for 3 more cameras: the Leica  M8, 
>>the Epson R-D1 and the Nikon D2h. For each camera I show an  image with no 
>>filtration, with IR cut, and IR pass, all at the same  exposure. Note how 
>>much IR is recorded by the M8--it is the most IR  sensitive of all the 
>>cameras. Note also how the IR contamination  has completely bleached the 
>>green out of the green pile blanket,  how the maroon blanket has shifted 
>>color, how there is a purple  sheen on the barrel of the Leica lens, and 
>>how the black pile  jacket has turned dark purple. The shot with IR cut 
>>filtration  knocks down the purple sheen on the lens barrel, improves 
>>color  saturation and contrast overall, but doesn't quite return the green 
>>  pile blanket to the correct color. Note also that there was a  glowing 
>>IR reflection from the "black" pile jacket on the bottom of  the apple 
>>which is taken out by the IR filtration.
>>
>>Similar comments apply to the Nikon D2h, but the infrared  sensitivity is 
>>weaker and the corrections with the IR cut filter  look better to my eye.
>>
>>The Leica M8 shot which has been filtered by application of the  profile 
>>Jamie Roberts supplied does have better blacks in the  anodized aluminum 
>>objects, but the green of the pile blanket at the  top has not been 
>>restored, and in general the colors of the pile  fabrics look faded.  More 
>>subtly, the IR reflection on the bottom  of the apple has not been 
>>removed.
>>
>>My point is that IR contamination doesn't just affect synthetic  black 
>>objects and dark anodized aluminum--it contaminates  practially all 
>>synthetic pile fabrics that I can find in my house.  So you can't just 
>>hunt down dark purple things and change their  color. (By the way, if you 
>>shoot social events and students in  classrooms in Seattle in the winter, 
>>you are going to encounter a  lot of pile jackets and incandescent light, 
>>so this is not some  obscure rare combination, at least for my use.)
>>
>>The Tiffen hot mirror filter which I used in these experiments is  
>>obviously too weak to restore all the colors (especially for the  green 
>>pile fabric), so I have a better UV/IR cut filter on order--a  Heliopan 
>>8152.
>>
>>Some philosophical notes:
>>
>>I have been using these other cameras for some time now, and I  always had 
>>more trouble getting indoor shots from the R-D1 and D2h  to look "right".  
>>There was some indescernible purpleness about  these photographs that 
>>reminded me of faded advertising posters. In  comparison the D200 
>>photographs looked rich and vibrant.  Now I  understand the source of the 
>>problem. I'll be using the IR cut  filters on the other cameras when the 
>>situation warrants.  I have  also noticed that foliage never looks right 
>>in the IR sensitive  cameras--it's always a funny spring green.  I will 
>>wager anything  that this comes from high IR reflections in plant leaves, 
>>even  under daylight.
>>
>>One huge difference between a film and digital camera is that the  
>>spectral sensitivity functions of the digital camera R, G, and B  channels 
>>are fixed forever.  You can't change the spectral  sensitivities by simply 
>>loading a different brand or type of film.  Since this is the case, I 
>>think it would make life easier for  serious photographers if digital 
>>camera manufacturers would measure  the spectral sensitivity functions of 
>>their cameras and publish  them, just as Kodak does with their films.  
>>With such a graph you  can tell at a glance if the camera has significant 
>>IR or UV  sensitivity, and you can pick your lens filters accordingly.
>>
>>
>>
>>
>>
>>
>>Mark Davison
>>
>>
>>
>>_______________________________________________
>>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



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