Experimental Work With UV Light Sources

[Erden]

Experimental Work

http://www.ultraviol...-light-sources/

15 February 2018

 

I carried out a learning exercise by illuminating a cultivated pink flannel flower (Actinotus forsythia) with a modified flash, sunlight and an UV torch. The images were processed using Lightroom 6 by following identical workflow except exposure adjustments.

 

The photographs were taken by attaching the lens to a Nikon PB-4 bellows at its maximum extension of 190mm to fill the frame with the flower which corresponds to magnification value of 0.65±0.02. Further magnification data for this assembly can be found at: https://www.flickr.c.../in/dateposted/ .The bellow & lens assembly was fully wrapped with a thick black fabric to eliminate any leakage of light. This issue had been addressed previously in web literature and it was also confirmed experimentally by me.

 

An Australian stingless bee, Tetragonula carbonaria (approximately 4mm long) is seen in the ultraviolet image taken by the flash.

 

Ultraviolet Light:Nikon D3200 Full spectrum modified, EL-Nikkor 150mm 1:2.8 metal body lens + Baader UV-Pass Filter 2”, Canon 199A modified flash, f/11 for 1.3" @ ISO 100.

Image Reference: ES1616-3

 

Ultraviolet Light: Nikon D3200 Full spectrum modified, EL-Nikkor 150mm 1:2.8 metal body lens + Baader UV-Pass Filter 2”, Bright sunlight, f/11 for 1.3" @ ISO 1600.

Image Reference: ES1627-2

 

Ultraviolet Light: Nikon D3200 Full spectrum modified, EL-Nikkor 150mm 1:2.8 metal body lens + Baader UV-Pass Filter 2”, Nichia NVSU233A diode torch, f/11 for 1.6" @ ISO 100.

Image Reference: ES1633-3

 

 

 

Published 15 February 2018

[Andrea B.]

Yes, this corresponds to what I've seen under UV-flash, sunlight and Nichia UV-Led.

 

But what was the ambient lighting under which each frame was made? Were you outdoors? Indoors?

[Erden]

I am glad to hear your confirmation which indicates that I am on the right tract. Next step is to carry out experiments on white balance issue that has been widely discussed in the forums.

 

The sunlight image was taken in the garden under bright sun at around 10:30AM. The flash image has also been produced in the daylight outdoors. However, the sun was behind the clouds for a while. When sun went behind the cloud the brightness of the image through the live view was quite dim. Then I switched on to the flash. In accordance with the comments of Cadmium and JCDowdy, this time I removed the filter sandwich from the flash and a noticeable increase in the flash output was reflected at the exposure value.

 

The photo taken with the UV torch was taken indoors without any significant daylight directly illuminating the subject.

[Cadmium]

White balance is really important, in the sense that all three pics would be mostly a product of white balance.

A 365nm Nichia torch pic would have a fairly monochrome reflected UV color. The 365nm light is fairly narrow, and not usually very interesting for reflected UV shots.

The Sunshine pic would usually have more range of color, and the flash pic should have more color than the Nichia.

I am not familiar with the UV color aspects of the flower you are shooting, however given good white balance for each shot I would expect the Nichia to look the most monochrome, and the other two to have more color than just monochrome.

So, yes, white balance...

If these all share the same in-camera white balance, then in that sense they are an interesting comparison of light source.

[Cadmium]

PS: I am not sure if I have 150mm El-Nikkor. I will go take a look.