[Leica] M8 Candles...

[kididdoc at cox.net (Steve Barbour)]

On Jan 7, 2007, at 4:34 PM, Peter Klein wrote:

> Whether part of an experiment or not, I think these candle shots  
> show something.  Now, we must stipulate that where Steve actually  
> focused may have been influenced by holiday spirit(s).  :-)  But  
> I've seen other M8 results with a similar effect. They point me to  
> the following working hypothesis.


careful now...   :-)
>
> In Steve's picture of Tom,
> http://gallery.leica-users.org/v/barbour/M8candles/tom.jpg.html
> notice that the the pendant around his neck is sharper than his  
> eyes.  This is even more apparent in the full-size version.   
> Assuming Steve focused on one of Tom's eyes

don't assume that Peter... you may assume that I focussed on the  
pendant,  and you would be right..  :-)


(it was too dark for the eyes...)

> , the plane of focus is farther away than where the rangefinder  
> told Steve to focus.
>
> Now, think about infrared photography.  I was just reading the old  
> Theo Kisselbach "The Leica Book," where he describes how to focus  
> for IR.  He mentions that you have to extend the lens further out  
> for IR photographs.  In other words, focus closer than the  
> rangefinder tells you to, because the IR image focuses as if it  
> were farther away than the visible light image.  He even gives  
> figures for lenses that don't have a special "R" mark for  
> infrared.  For example, to get IR in focus at infinity, you should  
> focus a 50mm lens on 15 meters (~50 feet).
>
> So, let's take a candlelight picture. We are focus the rangefinder  
> with the light we can see.  But there is a strong, invisible IR  
> component in the light, which is in focus a bit behind the visible  
> light focus point.  So, depending upon the ratio of IR to visible  
> light, we may get a picture that is:
>
> 1. Sharp at the point on which we focused (mostly visible light)
> 2. Sharp at a point slightly behind where we focused (mostly IR).
> 3. A bit blurry at both the visible and IR focus points (about  
> 50/50 ratio of IR to visible), because the OOF component of visible  
> light blurs the IR, and vice versa.
>
> The problem with all this is that our eyes can not tell us the  
> ratio of visible light to IR, as we can't see the latter.  I would  
> strongly suspect that candlelight has a higher percentage of IR in  
> its spectrum than does household tungsten bulb light, which is why  
> we see the more drastic focus shifts in candlelight pictures.  In  
> the latter, we have to contend only with dark fabrics (low visible  
> light) turning purple or shifting, but the IR/visible ratio is not  
> so high that we notice much focus shift.  (BTW, in Steve's picture,  
> Tom's shirt is distinctly purple if you boost the levels a bit).
>
> I should mention that I have seen a similar effect with red light  
> vs. green and blue.  I have lately been examining the individual R,  
> G, and B channels when I create B&W conversions of some of my E-1  
> photographs (thanks to Mark Davison for this tip).  The red channel  
> (longest visible wavelengths) always appears a little blurrier than  
> the others.  Which means that my Zuiko lenses are not apochromatic,  
> I guess.
>
> All this should be easy to prove or disprove.  Some enterprising M8  
> owner needs to take a few pictures of a focus chart at 45 degrees  
> to the lens axis, using both candle and tungsten light, both with  
> and without an IR cut filter.


not me...

Steve
>
> --Peter
>
> At 08:35 AM 1/7/2007 -0800, Steve Barbour <kididdoc@cox.net> wrote:
>> Leica M8,  firmware 1.09, Summilux 35mm/1.4 ASPH... all same lens,
>> same room, same evening, focussing... comme-ci comme-ca (some after
>> champagne)...
>>
>> 5 images are in this folder...
>>
>> http://gallery.leica-users.org/v/barbour/M8candles/
>> photos from New Years Eve...
>> (definitely NOT taken as part of an experiment)
>
>
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