Archived posting to the Leica Users Group, 2015/11/18

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Subject: [Leica] IR sharpness issues
From: hlritter at bex.net (Howard Ritter)
Date: Wed, 18 Nov 2015 09:37:56 -0500
References: <D136A0B8-DF27-4D2A-A29F-B5E5931BC19C@bex.net> <63B45E99-7733-43E2-A1D3-8B8005095AE6@frozenlight.eu>

I agree, Nathan. The sharpness issue is not terribly important to me either. 
It?s just that I was immediately struck by how unsharp the IR images were, 
and puzzled, because they were done at best focus as determined by trial and 
error. 

It?s become a brain-stimulation issue, as Frank said. For me, with a long 
background in astronomy and an interest in light and optics (as well as 
photography) from childhood, it?s a neat little problem in physical optics.

But that doesn?t stop me from loving the dramatic landscape alteration of IR 
imaging!

?howard


> On Nov 18, 2015, at 1:13 AM, Nathan Wajsman <photo at frozenlight.eu> 
> wrote:
> 
> 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/>
> http:// <http://www.greatpix.eu/>www.greatpix.eu
> PICTURE OF THE WEEK: http://www.fotocycle.dk/paws 
> <http://www.fotocycle.dk/paws>Blog: http://nathansmusings.wordpress.com/ 
> <http://nathansmusings.wordpress.com/>
> Cycling: http://www.crazyguyonabike.com/belgiangator 
> <http://www.crazyguyonabike.com/belgiangator>
> 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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> 
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In reply to: Message from hlritter at bex.net (Howard Ritter) ([Leica] IR sharpness issues)
Message from photo at frozenlight.eu (Nathan Wajsman) ([Leica] IR sharpness issues)