Tuesday, April 7, 2020

Reflected UV photography in polarized light IV - Saxifraga

Today more about UV polarizer experiments, using a special UV capable circular polarizer in front of my multispectral camera and UV-Nikkor 105mm lens, for recording polarized reflected UV images. Flower here was white Saxifraga - Rockfoil. UV filter used was my classic Baader-U filter; sun was used as light source.

[click on image gets you a larger image]

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

Saxifraga flowers through a rotating circular polarizer in A-mode i.e. exposure compensated...

Visible Light - Sunlight:

Reflected UV light - Sunlight:

Reflected UV light with 365nm UV LED:

Simulated bee vision - Sunlight:

This flower shows some interesting changes in polarization angle on the bottom of its flowers.  Bees have sensors on the outer ring of their compound eyes which are able to detect polarized light, so that might give this flower an advantage.

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 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 have written more about using UV polarizers HERE

More about Saxifraga in multispectral photography is HERE

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

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos