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Old 8th July 2018
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Re: m4/3 lenses for IR

I think the "hot spot" is coming from diffraction.

Some time back, I pressed to service my ever co-operative muse for this crude set of tests

With the camera set to f/22 and manual focus, I took 3 pictures.
The one above, with the bare flash, one with a Red gel over the flash and another with a Blue gel

I then removed the colour from the RAW files, examined them and cropped an area which I think best shows the effect.

RED Light

Blue Light

The filters used are very saturated "effects" filters and beyond any colours that you would get from natural light, but serve to show how the longer wavelength of the red light is diffracted more than the short wavelength blue light.

IR being even longer than the red I used will diffract even more through small holes...

We often repeat the mistakes we most enjoy...
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