Recently, an IR fanatic in Switzerland reached out to me and asked if I had thoughts about a filter that can produce deep lavendar foliage and deep blue skies.
I had found filters that could provide various levels of this effect when I first moved to Orlando in 2008. I pulled out my older set of filters and with a little iteration, was able to achieve the great combination of deep blue skies and lavendar foliage.
The effect works pretty well in a variety of lighting conditions, and allows a wide pallette of visible colors as well, such as yellows, reds, pinks and more, as seen in the rainbow color amphitheater along Lake Eola in Orlando.
It does seem to have some variance in light spectrum, that pointing angle and sun's azimuth in the sky (esp as it went lower) altered the white balance and low-angle scatter angle, even more than what was apparent to the naked eye.
Sky color varied a bit to, with time of day. A warmer blue (cyan) played on the sky later in the day, and cooler, deeper blue cast mid day.
I found I had to use a cloud or grey card to updat the custom white balance often, and even then it shifted often.
Below is the spectrum of the filter. Note the extra transmission in the deeper blue (400-450 nm), a small dip in the cyan-green (500 nm), dip green-yellow (575 nm), and a rise from the orange through the near infrared.
All of the colors are in there, but modulated. Again, the rainbow ampitheater shows its colors well. The closest commercial equivalent is the Lee gel L156 chocolate, followed by Rosco's e-color+ e156. Other potential candidates would be Rosco R99, their Permacolor P3114 (Victorian Gold) or possibly their R20.
This is defintely a fun filter to try out, just for the shear color depth and infrared effects.
