[Leica] IMGS: IR Attempts

[Howard L Ritter Jr]

Hi, Tina—

You may have missed the thread I initiated some time ago about this same thing.

You’re using the same camera and lens that I am, but your filter admits more visible deep red than my 093 filter. Are you focusing using one of the DOF lines to the right of the normal focus index? IR focuses as if the subject were closer than it is.

If you’re doing this, then you may be having the same problem that I am. My suspicion, though surprisingly i have not been able to confirm this despite extensive searching online, is that this lens (and perhaps lenses in general designed for conventional photography) is not achromatized for the IR range as it is for the visual spectrum. That means that IR of shorter wavelengths, say just over the line from deep red, is not brought to the same focal plane as IR of longer wavelengths from the very same subject. This of course is not an effect that can be compensated for by using a different focusing index. I shot the same scenes using every line from normal to f/22 as my focus index and could not get sharp images, though best results were at f/5.6. Shooting at a high f/ratio may help, though I couldn’t get rid of unsharpness even at f/22. But the same lens in visible light produces fine images.

If you’re NOT using, say, the f/5.6 DOF marker as the focusing index, then try that. If this is the case, I’ll be very interested in whether you get good sharpness. If you do, then my theory is down the drain.

See my results here <http://www.gallery.leica-users.org/v/hlritter/gallery/>. The degree of unsharpness that I get looks about the same as yours. People who get sharper results with IR photography than we do may be using filters that pass more deep red. If this deep red and near IR are much more intense than the deeper IR that passes our filters, and are mostly responsible for producing the image, and the lens is more nearly achromatic across this limited range that is closer to the visible, that may be why.

Good luck!

—howard



> On Aug 31, 2016, at 7:49 PM, Tina Manley <tmanley at gmail.com> wrote:
> 
> LUG:
> 
> After seeing the great IR photos posted here lately, I finally dug out my
> old M8s (the ones that fell in the river but are still working fine),
> charged up the batteries, and found a B+W 092 filter in the drawer that fit
> my 21/2.8 Elmarit.  I went out around the farm and photographed a few
> things.  Lots of problems.  Nothing looks sharp.  What am I doing wrong?
> None of the EXIF is right.  Most of these were made at ISO 160, around 5.6,
> and usually 1/30 or more exposure.
> 
> http://www.pbase.com/tinamanley/image/163998663
> 
> and the next 5.   Is there a trick to focusing with the dark filters?  I do
> like the tones so I would like to learn how to do this, but it has to be in
> focus to work for me!!  I got some great photos of the cat yawning that are
> so out of focus I won't bother to post them!!
> 
> TIA
> 
> Tina
> -- 
> Tina Manley
> www.tinamanley.com
> tina-manley.artistwebsites.com
> http://www.alamy.com/stock-photography/3B49552F-90A0-4D0A-A11D-2175C937AA91/Tina+Manley.html
> 
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