Full Spectrum Cameras IR Tutorials
Woody Bay Photographic
Full Spectrum Cameras
IR Tutorials
   
White Balance

Setting the White Balance before you start shooting is vitally important, unless shooting RAW, where it can be adjusted in the RAW Converter. On the Sony NEX cameras, select Colour




Filters

Assuming you are using a Full Spectrum camera, the best 2 filters to own for Infra Red are a Deep Red, such as a R25A filter which can be used for False Colour or Black and White, or a 720nm IR filter such as a R72 filter, which is mainly for Black and White. I often use the R25A when the sun is out and the R72 when its cloudy, but that is a generalistion. The R72 is easier to post process, whereas the R25A requires extensive Photoshop work to get the Gold Foliage effect, although you can do B&W's just as for a R72, but with a bit more control if required.

A R25A filter is approximately the same as a 590nm integral sensor filter , ie it blocks nearly all wavelengths of light shorter than 590nm and anything longer is allowed through. 590nm corresponds to red visible light, so the camera will see Red and Near Infra red up to the sensor's limit. Because the visible Red sensitivity of the cameras RGB sensor is maintained, the G and B sensors are sensitive to gradually longer IR wavelengths, which allows some degree of separation between the RGB channels. So if the R Channel is swapped for Blue in photoshop, and vice versa, then skies tend to come out blue and foliage comes out yellowy red or Gold with a bit of tinkering in photoshop, see below

A R72 filter is approximately the same as a 720nm ntegral sensor filter , ie it blocks nearly all wavelengths of light shorter than 720nm and anything longer is allowed through. 720nm is barely visible to the human eye and transmits Near Infra Red up to the sensor's limit. There is very little colour separation and so the False colours of the R25A filter are not really possible, however it does give darker richer skies and more contrast in foliage in B&W images than the R25A .

There are longer wavelength filter like 850nm and even 920nm filters which are even more dramatic then the R72, but they severely cut the sensitivity of the sensor so tend to need much longer exposures.

A UV/IR Cut filter is useful to return the camera to normal visible light sensitivity, similar to the filter that was removed from the camera in the conversion process. However, because it is unlikely to be exactly the same as the factory fitted filter the colour reproduction is likely to be slightly different and Auto White Balance [AWB]  and other pre selected colour settings on the camera are unlikely to be accurate. This means a custom White Balance will have to be performed again.  of the filter. Another problem is the IR blocking part of the filter is done by a Hot Mirror coating that reflects the IR light rather than absorbing it, this causes problems with wide angle lenses wider than about 28mm in full frame terms. The effect of the filter lessens as you go away from the centre, so the corners of the image tend to be discoloured by IR light leaking through.






Post Processing


















 
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