Pages

Ultraviolet Fluorescence

Diamonds

 

Ultraviolet light (UV) is invisible to the human eye but when certain substances are exposed to it, they emit visible light which we can see. This phenomenon is called fluorescence. I became interested in photographing fluorescence when a friend told me that scorpions appear bright blue under UV.  People rarely see scorpions because they are brown and well camouflaged but they are quite common where I live on the outskirts of Sydney and are easy to find at night by searching the leaf litter with a UV lamp.

My initial photos were disappointing because the backgrounds looked artificially coloured. I discovered that most ultraviolet sources, in addition to producing UV also emit coloured visible light and cameras often render reflected UV as unwanted colour. I built the equipment below to prevent false colours and a selection of images are shown below.

The essential components of my UV lamp, were purchased in 2018 from ebay for around AU$50 and include:

  • 10 watt 365nm UV LED. High output power of the LED reduces photographic exposure times and LEDs having wavelengths up to approximately 400 nanometres also work well.
  • Filter to block visible light emitted from the LED. This filter appears black but is transparent to UV. I used a "ZWB2" filter. This filter and a good UV led are the most important components needed to obtain good photos.
  • Resistor and heatsink to limit the maximum current and stop the LED from overheating
  • 3.6 volt rechargeable lithium cell, charger and switch
  • Condenser lens on the front of the lamp concentrates the UV into a brighter more intense beam which makes the fluorescence look more vibrant and reduces exposure times
  • To prevent unwanted ultraviolet light from reaching the camera sensor you can use a UV blocking filter on the camera lens. Many cameras record UV as colour and UV filters sold as "lens protectors" often do not block the longest ultraviolet wavelengths. A "UV(0)" or "L39"  filter stops nearly all reflected UV appearing as false colour in the image

 

UV lamp

 

Lens filter - Aluminium  foil, UV exposure for 20 seconds, f16, Nikon D750 with and without a suitable filter

 

Marbled scorpion - UV exposure for 6 seconds at f16 and fill flash. Nikon D750, 180mm lens with extension tube and tripod

 

Fledgling Powerful owl feather (left) and Sulphur-crested Cockatoo feather (right)

 

Diamonds and Rubies

 

 Australian $5 note

 

Eggs

 

Lichen growing on sandstone

 

 

 

 

Night photography

 Introduction

I have enjoyed photographing night creatures for over 35 years. With the rapid advancement in camera technology and LED illumination it is now possible to photograph birds flying at night and my techniques and equipment have evolved during those years. For this type of photography, the additional equipment can be as simple as a decent spotlight plus assistant or as complex as you wish. These are my thoughts and techniques as of February 2021.


Illumination

Photography in darkness requires either a continuous light source or electronic flash. There are several important differences between daylight and light sources which a night photographer needs to understand.

A fundamental of light is that the brightness of an illuminated subject, decreases in proportion to the square of the distance from the light source. For daylight photography, this fundamental can be ignored because the distance of the photographer does not change the brightness of the subject. When illuminated with artificial light, however, this is not the case as the diagram below illustrates. The diagram shows an object located at distance "d" is four times brighter than an object located twice as far away at distance "2d". Consequently, if the subject distance from the light source is doubled, the exposure needs to be increased by the equivalent of two f-stops and if it is halved, the exposure needs to be reduced by the equivalent of two f-stops.

 






Continuous lighting  - such as a spotlights is great for photographing stationary animals. Filament lamps and Xenon arc lamps produce light of excellent colour quality but are heavy and power hungry. LED spotlights and flashlights are portable, bright and energy efficient but most products produce light of poor colour quality. High colour quality LED lights having a high colour rendering index (CRI)  are becoming available and produce excellent results at comparable prices.

Exposure is determined using the camera metering system by adjusting shutter speed, aperture and ISO. The Tawny frogmouth below, was lit with the car high beam with camera settings of 1/15s, f5.3 and 9,000 ISO.

 

Electronic flash - is the ideal portable light source because it emits an extremely intense burst of light that can freeze movement of fast moving subjects. Flash units contain complex electronics that produce a short electrical discharge inside a transparent tube and when sufficient light has been emitted, the discharge is terminated by the clever electronics. The flash-tube contains xenon gas which produces intense white light of very high colour quality. Most models have auto-mode, however I prefer manual mode which controls the light output in f-stop increments.

To illustrate the advantage of manual flash over continuous light sources in freezing motion, I photographed an operating ceiling fan, with with black lines painted on one blade, at different shutter speeds and with different flash settings. Images in the top row were taken using a spotlight and camera shutter speeds from 1/500s  to 1/4000s. The bottom row was taken using a fixed shutter speed of 1/200s and electronic flash on power settings from full power to 1/32 power. Comparison of the images reveals that 1/4,000s shutter speed is equivalent to a flash flash power setting of 1/4 and the 1/32 power setting is estimated to be equivalent to a shutter speed of 1/20,000s.


Flash extender - With a telephoto lens at night, a fresnel lens located in front of the flash concentrates the light output providing a 3 f-stop gain in brightness. To illustrate this, the images below were taken using a 50mm lens with identical camera/flash settings and processing. The flash extender reduces the beam angle to produce a 'hotspot' which can be difficult to keep aligned when using a long telephoto lens.


 

Focusing at night

The different types of focus sensors in DSLR and in mirrorless cameras essentially measure subject contrast. The camera continually adjusts the lens focus until maximum contrast is obtained. Illumination intensity, subject contrast and movement, each affect the camera's ability to focus accurately and quickly and at night, high intensity illumination is necessary.

LED flashlights and bicycle headlamps provide sufficient light output to focus well on stationary subjects at night, however flying birds require much higher intensity. The human eye is a poor judge of light intensity and what may appear to be bright to the photographer may in fact be photographically very dim.


Exposure determination

With a continuous light source such as a spotlight, obtaining the correct exposure is identical to day-time photography.

Using flash, the task is more difficult. I set the flash mode to manual power because auto-flash usually produces disappointing results outside at night.

At the commencement of a night outing, I "calibrate" my camera/flash by taking a few test shots of an object such as a tree trunk, at a "typical" distance. My flash (with flash extender) set on 1/4 power, f8 and ISO 800 achieves good range and motion stopping ability at a distance of 10 metres.

For a different distance I adjust the ISO, aperture and flash power accordingly and where possible take images at different exposures.

 

Gear for night

When working from a car or with an assistant, photography in the dark is straightforward. When alone, simple tasks including, changing settings, and adjusting gear are difficult and error prone. It is a great help to pre-configure as many settings as possible and get your gear ready before nightfall. My current setup shown below  consists of a rigid carbon fibre bracket containing a rechargeable spotlight and TTL cable and weighs 750g. On maximum power, the spotlight produces 700 lux at a distance of 10m which makes it possible to lock focus on birds flying at night at distances of at least 20m.

 
 

Tripod - A tripod is a useful adjunct for photographing at fixed locations such as roosts or nests. A small lightweight carbon-fibre tripod to support the camera or as a stand for an off-camera flash is ideal.

Slaves and triggers - Occasionally, I use off-camera flash triggered by sync. cables or Pocket Wizzard Plus-X radio triggers. Previously, I used Nikon's clever inbuilt 'CLS' system which uses line of sight infrared communication between camera and flash. Unfortunately, it is time consuming to set up and unreliable in the bush due to  beam path obstructions from unseen objects such as leaves and branches.

 

Camera settings

Settings Banks - Many cameras allow you to save your favourite settings for quick recall. My camera has two banks which I have configured for night use, one for flying birds and the other for stationary subjects. It saves enormous time and frustration being able to select pre-configured settings by simply rotating a knob.

Image format - RAW file format has high dynamic range and a high capacity for correcting white balance and for salvaging shots which would have been spoilt by over or under exposure had they been taken in jpeg format.


LCD Monitor - At night the monitor screen appears very much brighter than it does during the day and images which appear adequately exposed are often seriously underexposed. To counteract this, I turn the monitor brightness right down and where possible check the image histogram after the exposure.

 
Shooting Mode - My camera is always set to manual mode because I always use manual flash at night.


Focus - For stationary birds I use the centre autofocus point and continuous focus with the camera set for 'backbutton autofocus'. Backbutton focussing makes it easy to reframe the subject without  refocusing. For flying birds, I use continuous autofocus and multiple focus points, with the shutter shutter release button set to "focus and shoot". Camera brands and models have a multitude of focus modes and I am not sufficiently knowledgeable to expound on which ones are optimal.


ISO - Producing sufficient light to properly expose the image or to obtain a 'motion-free' image can be difficult. Using higher ISO is equivalent to using a more powerful flash unit, however the downside is that it increases image noise. On my camera ISO 800 produces an acceptable level of noise and I use that as my go-to night setting.


Aperture - A wide aperture is often desirable to isolate the subject from the background and increase the maximum working range of the flash. The downside is that accurate focus is even more critical and some lenses are softer at their widest aperture.


Shutter - When using a camera with focal plane shutter, the maximum shutter speed should not be set higher than the maximum flash sync speed, which is around 1/200s for most models. At night, the surrounds are dark and it is the short duration of the the flash which stops motion, not the camera shutter speed.

Slow shutter speed in low light can be useful for stationary subjects to record ambient light as shown for the Barking owl below, which was taken at 1/15s. The owl remained sharp because it was exposed by the flash, whilst the background shows some blur from hand-held camera movement.

 


Illusion of speed - Flash combined with low shutter speed can be used
to give the illusion of speed. For the Nightjar below, a sharp image of the bird was produced by the short duration of the flash which is superimposed on a blurry image produced by the slow 1/30s shutter speed and the focus light. By setting the camera flash mode to 'rear-curtain sync', the blurred image trails the bird giving the impression of speed.

 

 

This technique is often a bit of a gamble as a potentially good image of a difficult to photograph subject, such as the Grass owl with prey below, is ruined.

 

 

Nocturnal Eyes

Pupils - A continuous light always produces contracted pupils when the bird is looking toward it and there is no way to prevent that. This is especially noticeable for a bird having a light coloured iris such as the young Boobook owl on the left below. Large eyes are a prominent feature of nocturnal birds and if we were able see in the dark we would see that their pupils are always wide open. To me, dilated pupils look natural and can be captured by pre-focusing then turning off the focus light a couple of seconds before releasing the shutter, as shown for the Boobook on the right below.

 

Red-eye

Red-eye occurs when the light source is located 'close' to the camera and light is reflected from the retina of the eye into the camera lens. By moving the light source away from the camera or moving closer to the subject red-eye can be reduced or avoided. This is illustrated in the diagram below and in the images of a Tasmanian Boobook owl, taken at different distances and head angles. Increasing the angle can be achieved via a camera bracket or using off-camera flash.


 

Sometimes you cannot avoid red-eye as seen in the left and centre images above, however it can often be 'fixed' by photo-editing. Pupils almost always have some light and colour, so I prefer to darken them by 'burning' the shadows and mid-tones, then desaturating the colour until they are almost black. You can also 'dodge' the catchlights and eye reflections to enhance their appearance as shown for the same images below.

 

 

Flying birds

Flying birds present the ultimate challenge. Sharp images can be obtained by shooting a bird leaving or arriving at a pre-focused destination or by achieving focus in flight. The Tawny frogmouth below was taken by pre-focusing on the perch it was using for hunting and by watching with a dim red light until it flew. The Grass owl was focused in flight using the camera bracket detailed above.

 Conclusion

My thoughts and ideas are intended as a guide for those interested in night photography. They should not be considered binding, rather as ideas and techniques that have worked for me and can be improved upon. I hope this article can assist you in developing yours night photography skills and encourage you to give it a go.

Night observation

Night observation is very different from observation during daylight. At night we rely on our sense of hearing combined with sight and artificial light to locate animals. Nocturnal animals have acute senses compared to us and they are usually aware of our presence long before we see them. Often I find an animal by its call or the noise it makes as it moves, then I locate it by eye-shine.

 

Attraction aids

Many animals can be attracted by playing their calls and sometimes the calls of other species. Recorded calls are often used during owl surveys, by photographers and I  use them when looking for owls at new locations. Call playback can be highly disruptive and stressful to the animal if not used judiciously and I do not encourage its general use. Playback should be avoided near nest sites during the breeding season. Owls are strongly territorial so you should resist the temptation of divulging their locations to other photographers and twitchers, as the owls are sure to be harassed.

 

Vision

Vision is a complex sense which involves signals from the eyes which are interpreted by the brain. The retina at the back of the eye contains two fundamental types of light receptor cells, called cones and rods. Cones only work in bright light and rods only work in dim light. Diurnal animals including humans have cone dominated vision which enables excellent perception of colour with high visual acuity in daylight. Most nocturnal animals have eyes with relatively few cones and an abundance of rods which makes for excellent night vision but comparatively poor daylight vision. 

There are several cone types, each having a peak sensitivity to a different light wavelength. The brain 'sees' colour; not the eyes and it does this by combining the signals from each cone type, analogous to mixing primary paint colours to achieve all the colours of the rainbow. The more cone types a species has, the better its ability to distinguish colours. Mammals have either two or three cone types whilst birds, reptiles and fish have four, which provides them with superior colour perception and the ability to see ultraviolet light.

The graph below shows the colour sensitivity of the three types of cone cells in the human eye.

In very dim light cone cells don't function and the brain receives signals from the rod cells only. Rod cells in the human eye enable low light vision with poor visual acuity and no perception of colour. The images below are of a bioluminescent fungus. The upper view  shows how our eyes see the fungus at night and the lower view shows the true colour and high sharpness as seen by the camera.

 

 

Rod cells in the human eye and nocturnal animals have a spectral sensitivity of 400-600nm (see graph below) and are completely insensitive to red light (620-680nm). The significance of this is that you can observe most nocturnal animals with a dim red light without causing them excessive disturbance. Most animals can can see a red lamp, because their eyes also contain low concentrations of red sensitive cones.

 

White light

Intense white light torches and spotlights are great for finding animals but are not well suited to studying nocturnal behaviour or watching nesting owls. White light has the advantage that we can see the true colour of an animal's eye-shine, which can be useful for identification at distance. During a holiday in Sabah, Borneo, I heard a creature on the forest floor in the grounds of the hotel I was staying at. With the aid of a LED torch, I located it by its beautiful blue eye-shine (below) and it was a Mouse deer, not much larger than a rabbit. Bright white light can cause temporary night blindness lasting at least 10 minutes, during which time the animal may become susceptible to predation.

 

 

Red light

Rods don't see red, so for observing animals at night, headlamps that use red LED's are ideal. Dim red light does not disrupt an animal's night vision or your own. My favourite headlamp below, comprises a lens, a 3 watt red LED, a resistor to limit the current, a switch and a 3.7 volt rechargeable battery. It can be attached to a tripod and the beam can be focused or spread to control the width and brightness. The main disadvantage of using red light is that everything appears red.

 

 

With red light, you are able to watch and photograph nocturnal animals behaving naturally. The photo below of a nesting Powerful owl was a 1/3 second exposure at f6.3 and ISO 6400 illuminated with the headlamp shown above. I observed this nest for many years using red light and the owls were always aware of my presence but were unconcerned. I watched this adult leave the hollow on dark and return a short time later with a Ringtail possum to feed its young. If white light was used, it probably would not have returned whilst I was watching or it may have abandoned its nest.

 

 

 

Walking at night

Long-sleeved shirt, long pants and sturdy boots are essential  to protect yourself from cuts, scratches and bites when walking in the bush at night. I prefer to walk along tracks rather than through bush because you can move quietly and are likely to see more animals. Depending on the weather and where I am, I may also take extra clothing, food, water, insect repellent, first aid kit and something to sit on. Unnecessary gear can turn a casual walk into a hard slog so I try to carry only the essentials.

Being in the bush by yourself can be very rewarding and you usually locate more animals when you are alone because your senses are heightened, however you need to be better prepared. In the dark your vision and sense of direction is poor and it is easy to become disoriented or fall on something you didn't see. When I venture out alone I always:

·     Tell someone where I am going and when I expect to return

·     Know my exact location at all times and if unsure, stop until I have worked it out

·     Stay on the intended route unless I am familiar with the area or am carrying  navigation aids

·     When I venture off-track I always watch where I place my footsteps to avoid falling.

 

Richard Jackson

 

 

As a child I grew up in the northern suburbs of Sydney with Ku-ring-gai Chase National Park as my back yard. After school and on weekends I would spend countless hours with my best friend and school mates exploring the bush, catching tadpoles, yabbies and cicadas, damming creeks and playing hide and seek.

 

During those years I developed a love for the bush and became interested in the various birds and mammals that lived around me. I was always fascinated by the wonderful wildlife photos in National Geographic magazine and was in awe of the SLR film cameras advertised on the back page. My passion for nature photography started at age fourteen when my parents bought me my first camera, a Kodak Instamatic. Dreams of magazine images were shattered when my first roll of film was developed and the beautiful Robin I photographed in my mother's rose garden appeared as a scarlet speck.

 

By age seventeen I had saved enough money for a Nikon F2 SLR camera and 300mm lens which my father purchased for me, duty-free. Without success in achieving the stunning images I dreamed of, my interest in wildlife photography faded until after my first child was born. It was then when free time was scarce, I decided one night to venture into the Royal National Park, near my home in Engadine, to see if there were any animals about. To my surprise and delight I saw possums and watched a Tawny Frogmouth fly to a dead limb, close enough for me to photograph.

 

After overcoming my fear of the dark I quickly started enjoying the solitude of being alone in a world of nocturnal creatures and the uncertainty and excitement of what I may find. With the advent of affordable digital cameras with fast and accurate autofocus it became much easier to take quality images at night and I now look at my prized SLR photos from the past and keep them as momentos.

 

My main photographic interest is in owls and nocturnal mammals and therefore I love nothing more than heading into the bush when most people are calling it a day. As the sun sets a world few are aware of awakens, where I observe creatures that most only see in books.

 

I owe my continued interest in this hobby to Julie my wife for her loving support and ongoing encouragement for over thirty years. Thank you to Gerard Satherly who built this website for me and to the friends I have made at Feathers & Photos forum who have taught me so much about photography.

 

You are welcome to use any of my images for your personal not-for-profit use such as projects etc, but please reference me as the photographer. My images are copyright so if you would like to use an image for any other purpose please contact me. My e-mail address is prsj56[at]optusnet.com.au