We have covered UV spectrum and sources of UV light in our earlier blog. We will cover the basic techniques of UV Photography using the ubiquitous digital cameras in this blog. For our “experiments” we have used a not so expensive Olympus SP 510 UZ digital camera which has a 7 mega pixel resolution and a 10 X optical Zoom.
There are 2 ways you can capture images under UV illumination – one to exclude all available light using a UV pass filter like a Wratten 18A or use a darkened room and light up the subject using UV light alone. We will use the latter method as it is the easiest way to gain some valuable experience with minimum outlay in terms of equipment.
You will need a robust tripod, a UV fluorescent light (in our case we used the 6 inch F6T5/BLB tube) and your trusty digital camera. The BLB tube indicates that it has a Black Light Blue which produces output in the UV-A spectrum.
Select your subject and position that in a room with all blinds drawn. Light up the subject with a similar 6 inch fluorescent tube. Ideally both the normal light and the UV light should be placed in the same position facing the subject. Set up the camera on a tripod and switch off all the lights except the normal small tube light. Switch into manual mode in the digital camera. This allows you to set the long exposure required to capture the subject lit only by the UV light. The metering system in your camera would have been optimized for visible light spectrum.
Focus the camera and set the exposure for the visible light. Observe the first photograph here which shows a flower urn with artificial flowers. We used f /5 aperture at 1 second shutter speed settings for this shot. These figures are approximate and you may need to experiment depending upon your camera equipment and lighting factors.
Now turn off the normal light and switch on the UV fluorescent tube. Change the shutter speed to at least one second if your subject is not the fluorescing kind. Your subject and its susceptibility to fluoresce determines the eventual exposure settings. You may have to bracket the shots for optimum results. We used the same aperture with 3 seconds shutter speed for this UV photo.
Notice the UV lit flower urn and the color fringing effect possibly owing to the long exposure time and chromatic aberration due to the achromatic lenses used in our camera.
You can use a smaller aperture to reduce this chromatic aberration which occurs due to the slight change in focus for different light spectrum. You will have to increase the lighting for non fluorescing objects for best results.
For subjects which fluoresce under UV lighting, you will have to place the lighting in a such a way as to avoid reflections back to the camera lens which will affect the eventual image.
Observe the glowing plastic in our previous blog. It is an overexposed shot. If you leave on the automatic mode, your camera’s metering system will always over expose the shots when the subject is lit only by a UV light source.
Noting Down Information:
In the days of film cameras one would have to write down the settings in a notebook for future reference. With digital cameras, this is no longer necessary as you can refer to the Exif (Exchangeable image file format) of the picture directly.
In Windows XP and later, right click on the image file and select Properties from the Popup menu and then click on Summary – > Advanced and you can see the photograph information.
In Unix/Linux environment, if you use KDE, then the same drill of right clicking and Properties and then “Meta info” will extract all the Exif information.
This way you can improve your technique of the right exposure for the right subject.
A long time ago, I read “the case of the Drowsy Mosquito”, a novel by Erle Stanley Gardner in which the legal eagle Perry Mason in his attempt to solve a murder spends a night in a mining town. He hears a disturbing sound in the still of the night – a drowsy mosquito. Actually it is the sound of an Ultra violet lamp used by the killer to look for some treasure. When I think back now, I think it must have started my fascination with exploring the world under a new “light”.
Ultra violet photography is a very interesting field and with the advent of digital cameras it is possible for almost anyone to explore this fascinating field.
Ultra Violet or UV falls into this range – from 100 nm to 400 nm. High school physics tells you that the visible light spectrum spreads from 400 nm (violet) to 700 nm (red).
The electromagnetic energy covers a wide spectrum and the visible light waves form a smaller part.
The energy level depends on the wave length and at some intensity can cause damage to living organism.
Ultra violet can be further divided into 3 categories based on the wavelength.
- Short Wave Ultra Violet (UV-C): This covers the region of 200 – 280 nm. This light is dangerous and thus mostly used for germicidal application – sterilization and disinfection like purifying water and food.
- Medium Wave Ultra Violet (UV-B): This covers the region of 280 – 315 nm. This light causes sun burn if exposed for a longer duration and is implicated in skin cancer under prolonged exposure. It is used for tanning and curing some material.
- Long Wave Ultra Violet (UV-A): This covers the region of 315 – 400 nm. This light range is used for special effects and called as Black Light.
Ultra violet irradiation is often used for food processing and UV lights are used in industries and forensics.
Sources of UV Light:
Fluorescent bulbs with Wood’s glass – often called as Black Light are the most popular. They are called as BLB (Black Light Blue). These lamps have a darkened blue outer glass – hence the name. The kind of lamps you see in CSI TV serials is probably this type. This BLB produces output in the UV-A spectrum.
These lamps are used in entertainment applications, forensics and for checking counterfeit notes. You can use these lamps to light up your subjects for UV Photography with out needing to spend a fortune on expensive filters.
The water filter kind of Fluorescent bulb which puts out energy in UV-B range has normal clear outer glass.
Other major sources are Mercury Xenon Arc lamps, Mercury Vapor Lamps, UV LEDs (which produce output in the range of 380 to 400 nm) and Metal Halide Arc lamps to name a few.
Subjects for UV Photography:
You have a whole world of subjects to be captured under the glaring lights of UV. Many objects exhibit certain amount of fluorescence under UV illumination. Fluorescence is the effect that happens when an object absorbs light at a particular wavelength and releases a longer wave length light. Many special dyes glow under UV light.
Generally white objects tend to reflect UV light back making it appear brighter.
Some plastics glow under UV lights. Many materials like minerals, gems, body fluids and chemical markers or dyes fluoresce to varying degrees under UV lights.
Plants having chlorophyll which gives them the characteristic green color fluoresce to red glow under UV lighting. From antifreeze to club soda many common items exhibit fluorescence under UV. Vitamins A and Vitamin B – niacin and thiamine will fluoresce to yellow color when lit by UV.
Tooth whiteners and detergents exhibit fluorescence too. Many Flowers, bird plumage and fish skin appear differently under UV than they appear under normal light. Many animals have visual response which covers a wider spectrum than for the humans. May be their world is far richer in color than ours.
We will cover the basic techniques of UV Photography in a subsequent blog.