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Old 9th July 2018
MikeOxon MikeOxon is offline
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Re: m4/3 lenses for IR

An unconverted camera can also provide the infra-red effect, albeit at the expense of long exposures. I have a set of Schott long-pass filters and experimented with these on my E-M1-ii camera with 17mm f/2.8 lens (chosen because my 25mm diameter filters cover the small-diameter lens)

The results are shown below - note that the exposure increases from 1/400s@f/8 for the unfiltered shot to 1/10s@f/2.8 when the red (RG645) filter is applied. The exposure increases further as the cut-off wavelength moves into the infra-red.

Also notice how the sky becomes black and the green foliage becomes bright, once the cut-off wavelength reaches 780nm. By this point, the Bayer filter array no longer works and all three filter components (red, green, blue) start to transmit, so distorting the 'colour' that is recorded by the sensor.

I believe that this is why bright red subjects, such as roses in strong sunlight, acquire a magenta tinge, since these flowers reflect a large amount of infra-red radiation. I usually darken the magenta component of images of such subjects, to restore the red colour that we actually see directly.
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