For those interested in photography “beyond the visible”, some of the filters available from Midwest Optical Technologies Inc. under the MIDOPT brand name should be very interesting. They are distributed in European countries by Stemmer AG. Both companies are specialised in the supply of machine vision equipment. What adds additional interest is that filters are supplied in very many different sizes (from M13.25 all the way to M105, mounted and unmounted, and even with mounts suitable for installation at the back of objectives with C-mount).
Not only long pass filters are listed in the catalogue, but also several NIR bandpass filters. Even more interesting are double and triple band pass filters. These filters on a broad-spectrum converted camera should tweak the sensitivity of the RGB Bayer-array channels in the sensors to narrow their spectral sensitivity or “move” one of the channels to the NIR. For example for B/G/NIR response the filter TB475/550/850. (The plot bellow is from the published specifications given with 10 nm steps, which results in “odd” shaped peaks.)
Also a narrow band-pass interference filter at the “red edge” of leaves’ absorption spectrum is advertised as suitable for diagnosing “plants’ health”.
In this case the filters offered are less unusual. Mostly filters with the expected NIR leakage. On the other hand many of the VIS pass and UV and NIR blocking filters in the MIDOPT catalogue could possibly be very good for UV- and VIS-induced imaging of fluorescence in plants.
It is difficult to work-out from the spectra whether any of the UV/NIR cut filters would be good for improving the white balance of full-spectrum converted cameras when used in VIS light.
I have requested price quotes from Stemmer AG for the two filters whose spectra are shown above, plus for a NIR long-pass filter suitable for use with illumination from 940 nm LEDs. [Update 2018-01-23] I have received quotations some days ago, I just mention approximate prices as these may vary. Prices for 52 mm filters are in line with what one would expect for interference filters, in the range of 450 to 300 €.
All illustrations and text are of my own authorship, and copyrighted.
(c) 2017 Pedro J. Aphalo