[Leica] IR sharpness issues

[photo at frozenlight.eu (Nathan Wajsman)]

Howard, a couple of things:

- George suggested a procedure for testing sharpness with the camera on 
tripod etc. to determine the focus compensation needed. If you really worry 
about sharpness, then do what he suggested.

But?

- for me, IR photography is less about sharpness and more about tonality and 
the special IR effect. In fact, I do not even bother with the focus 
compensation. When I shoot IR, I just focus normally. Most of the time, the 
subjects are anyway far enough away that precise focus does not matter that 
much.

And finally, do not bother shooting IR on a cloudy autumn day. You need 
plenty of sunshine for good IR. Although the pictures you posted earlier 
very nice.

Cheers,
Nathan

Nathan Wajsman
Alicante, Spain
http://www.frozenlight.eu <http://www.frozenlight.eu/>
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YNWA













> On 17 Nov 2015, at 22:33, Howard Ritter <hlritter at bex.net> wrote:
> 
> More experimenting.
> 
> Today I took some photos with the M8 and Elmarit-M 24/2.8 both with and 
> without the IR filter because I was unhappy with what appeared to be very 
> soft focus in the IR photos from yesterday.
> 
> The first thing I found is that with the B+W 093 (830 nm) filter, an 
> exposure compensation of about 5 stops is needed. When the subject is 
> predominantly cloudy sky, it?s more like 8 stops,  clouds, like blue sky, 
> apparently being relatively IR ?cool".
> 
> The second thing I found is that the sharpness of the images taken through 
> the IR filter really is dismal. Here?s a small crop of the frame with the 
> IR filter:
>       
> http://gallery.leica-users.org/v/hlritter/For+Gallery/43+IR+tree+crop.jpg.html
>  
> <http://gallery.leica-users.org/v/hlritter/For+Gallery/43+IR+tree+crop.jpg.html>
> 
> And without the filter:
>       
> http://gallery.leica-users.org/v/hlritter/For+Gallery/47+IR+tree+crop.jpg.html
>  
> <http://gallery.leica-users.org/v/hlritter/For+Gallery/47+IR+tree+crop.jpg.html>
> 
> 
> Aperture was f/2.8 for both. Focus was compensated (f/5.6 mark) for the IR.
> 
> Any thoughts on the dramatic difference in sharpness between the two? 
> Given that the filter is a genuine B+W from B&H, I?m thinking it?s not 
> because of lousy glass. The only other thing I can think of is that the 
> lens might not be achromatic for the full range of IR wavelengths passed 
> by the filter and detected by the sensor, so that in wavelengths 
> progressively further from the one that?s exactly focused, their 
> contribution to the image is progressively further out of focus.
> 
> 
> ?howard
> 
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