Wednesday, March 18, 2020

Reflected UV photography in polarized light I

Today about an experiment I have done, using a special UV polarizer made by Zeiss in front of my multispectral camera and UV-Nikkor 105mm lens for recording reflected UV images. This UV-Polarizer was especially made to work down to 300nm with some rather flat transmission and a 99-100% polarizing effectiveness in the 300-700nm range. It was part of a laboratory set of several UV-VIS-IR polarizers and wave plates I luckily acquired recently from a retired head of development. UV filter used was my classic Baader-U filter; sun was used as light source.

[click on image gets you a larger image]

Here the  transmission (linear scale) and absorbance (log scale) spectra of these polarizers:

Here now some of the photographic results I got (took multiple images while rotating the filter), presented as animated gifs....

Roofs of some neighbouring houses:

Flowering succulent plant (Cliff maids - Lewisia cotyledon):

Butterfly orchid - Phalaenopsis:

Reflected UV photography in polarized light shows quite some usefulness, especially if there are (glossy) surfaces which change the polarization angle of light and which the polarizer filter makes visible. Downside is that one needs about 2 stops more exposure, due to the low approx. 25% transmission.

Some may have noticed the change of focus, which might be caused by some unevenness of that special polarizing filter foil; it will be investigated later.

Some insects are able to see the polarization angle (and btw. we humans can also, but needs some traing: Haidinger's Brush) especially honeybees which navigate using the polarization angle of ultraviolet (UV) light.

I will make further tests later using the other polarizers and also the special waveplates, which allow for circular polarized light.

Stay tuned, more will follow on that fascinating subject...

More info on this very interesting field may be found on my site