[Leica] IR sharpness issues

[Howard Ritter]

Next up: a test in bright sunlight, small aperture, windless day, and tiny steps through the focusing range. Today’s weather forecast doesn’t look promising.

My prediction: it will make no difference. The air was quiet that day, my friends (apologies to George Costanza), so the long shutter wouldn’t have come into play, and anyway the lack of sharpness is present everywhere, and is not a lateral streaking as motion would produce. I had stepped carefully through the focusing range (1/2 stop steps). I had enhanced the contrast by stretching the tonal range to span the whole histogram, and the IR image seems pretty clearly, no pun intended, to be unfocused rather than of low contrast.

I’m sticking with my theory of chromatic aberration, since there would be no apparent reason for lens designers to make a lens achromatic across the IR range.

Are you in a position/of an inclination to take quick test shots of a subject at practical infinity both with and without the filter, crop a small detail from each shot, and post them? I’d be very interested in whether anyone is getting IR photos that are sharp under close examination.

—howard


> On Nov 18, 2015, at 9:55 AM, George Lottermoser <george.imagist at icloud.com> wrote:
> 
> If I had to guess…
> which I do…
> 
> You're looking at a combination of:
> Slow shutter speed
> Branches moving in the breeze
> Improper focus
> A reduction of micro contrast in the IR range
> 
> The focus issue stumped me too
> until I ran the tests
> and locked in on a specific lens
> which performed well with IR on M8
> and found that magic focus shift point on the lens barrel.
> 
> Using that focus shift point
> has a profound effect at all focus distances
> even on subjects 200 meters away;
> which surprised me.
> Because you'd, or at least I'd, have thought
> that "depth of field" would have made its use negligible.
> 
> And the testing also demonstrated that it is a precise point on the lens barrel.
> Even slight variations left or right of the "the point"
> DO have an effect on "focus."
> 
> a note off the iPad, George
> 
> On Nov 17, 2015, at 3:33 PM, Howard Ritter <hlritter at bex.net> wrote:
> 
>> Any thoughts on the dramatic difference in sharpness between the two?
> 
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