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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 made the equipment described below to prevent false colours appearing and a selection of images showing fluorescence 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 30 years and my ideas and equipment have continually evolved. With the rapid advancement in camera technology and the advent of LED illumination it is now possible to photograph birds flying at night. This trend will continue and the techniques and equipment I use today will quickly become outdated. For those interested in this type of photography the additional equipment that is needed can be as simple as a decent spotlight and an assistant or as complex as you wish. These are my thoughts and techniques as of September 2019, which I hope will provide insight and tempt you to venture out at night and enjoy your photography in a different light.


Illumination

Photography in darkness requires the use of artificial light in the form of either a continuous light source or electronic flash. There are several important differences between daylight and light sources which the experienced night photographer understands.

A fundamental characteristic of light is that the brightness of an object, decreases in proportion to the square of the object distance from the light source. The diagram below shows that if an object is located at "d" it would be four times brighter than if it was located at "2d". Each time the distance to the light source is doubled, the correct exposure needs to be increased by the equivalent of two f-stops. Likewise, if the distance is halved the exposure needs to be reduced by the equivalent of two f-stops.

For outdoor photography during daylight, the sun is so far away from planet Earth that the brightness of any object due to its distance from the sun is essentially the same and can be ignored. However, a hypothetical photographer on planet Jupiter which is 5 times further away from the sun, would need to increase the exposure by 25 f-stops!






Continuous light sources  - such as spotlights are great for photographing animals that are stationary. Filament and Xenon arc lamps produce light of good colour quality but are power hungry and heavy by today's standards. LED lights are portable, bright and energy efficient  but most produce white light of  poor colour quality. Lights having  high quality white LED's (high CRI) are now becoming available at lower cost.

Exposure is determined using the camera metering system by adjusting shutter speed, aperture and ISO. The Tawny Frogmouth below, was sitting on a post and the car headlights were used for illumination with camera setting of 1/15s, f5.3 and 9,000 ISO.

 

Electronic flash - the ideal portable light source. Flash units contain complex electronics that produce an electrical discharge inside a transparent tube. When sufficient light has been emitted the discharge is terminated. The flash-tube contains xenon gas which produces intense light having a white balance comparable with midday sunlight. Most models have an auto-mode, however I prefer manual power settings which controls the light output in f-stop increments.

The composite image below is of an operating ceiling fan. One blade was painted on the edge with white paint and black lines. Images in the top row were taken using continuous light and show the effect of camera shutter speed in stopping motion. The bottom row, taken using an electronic flash on different power settings at a camera shutter speed of 1/200s, illustrates the superior motion stopping ability of electronic flash. Comparison of the images also reveals that the maximum 1/4,000s shutter speed on my camera is equivalent to a power setting of 1/4 and the motion stopping ability of the 1/32 power setting is equivalent to a staggering shutter speed of around 1/20,000s.


Fresnel lens flash extender - a Fresnel lens placed in front of the flash is a useful aid to a telephoto lens at night. It concentrates the light into a narrow beam, typically providing a 2-3 f-stop gain in brightness. To illustrate this, the images below were taken using a 50mm lens with identical camera/flash settings and image processing. A flash extender produces a major gain in brightness  but is difficult to keep aligned with the field of view through the lens. I use a rigid carbon fibre bracket to counteract this problem.

 

Focusing at night

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

LED flashlights and spotlights provide sufficient light output to focus on stationary subjects, however flying birds require intense illumination.


Exposure determination

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

Using flash, the task is more difficult. I set the flash mode to manual power, rather than on auto-flash, which often produces disappointing results when used outside at night.

At the commencement of a night outing, I "calibrate" my camera/flash set-up by taking test shots of an object such as a tree trunk, at a "typical" distance. My flash 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 a trial shot.

 

Gear for night

When working from a car or with an assistant, photography in the dark is straightforward. When alone, simple tasks such as changing camera settings, adjusting gear and lights are difficult and error prone. It is a great help to pre-configure as many settings as possible and have your gear setup before complete darkness falls. My general setup shown below, is based on a rigid carbon fibre bracket which can incorporate a camera mounted via the baseplate (70-300 mm zoom) or the lens-foot (500 mm lens). The focussing lights produce 450 lux at a distance of 10m which makes it possible to photograph birds flying in the dark.

Tripod - A tripod is useful for photographing subjects 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 including 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 the desired settings by rotating a knob.

Image format - RAW file format has a much higher capacity for correcting white balance and for salvaging great shots which would have be spoilt by over or under exposure if they were created as JPG files.


LCD Monitor - The monitor screen appears very much brighter at night than it does during the day and often, images which look adequately exposed are considerably underexposed. I turn the monitor brightness right down and where possible also check the image histogram to see if the exposure was OK.

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


Focus - For stationary birds I use the centre autofocus point, continuous focus and have the camera set for 'backbutton autofocus'. Backbutton focussing makes it easy to reframe the subject without  refocusing. For flying birds, I use continuous autofocus with multiple focus points selected and use the shutter release button 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 high ISO is equivalent to using a more powerful flash unit, however the downside is that it also increases image noise. ISO 800 produces an acceptable level of image noise on my camera (Nikon D750) and I use it as my go-to night setting.


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


Shutter - When using a camera with focal plane shutter, the maximum shutter speed should be set no 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 pulse of light from the flash which stops motion, not the shutter speed.

Slow shutter speeds, however, can be useful for stationary subjects to record ambient light detail as shown for the Barking owl below, which was taken at 1/15s. The owl remained sharp because it was exposed by flash, whilst the background shows some effects of camera movement.

 

Flash in conjunction with a low shutter speed can be intentionally combined to give the appearance of motion as shown for the Nightjar below. A sharp image of the bird was produced by the short duration of the flash and the blurred trail resulted from the 1/30s shutter speed exposure from the focussing light. By setting the camera flash mode to 'rear-curtain sync',  the blurr can be made to trail the bird to give the impression of speed. 

 

 

More often than not though, an otherwise good images of difficult to photograph  subjects, such as the Grass owl below, are ruined.

 

 

Nocturnal Eyes

Pupils - Unfortunately, a continuous light always produces contracted pupils when the bird is looking toward it and this is especially noticeable with birds having a light coloured iris as is apparent for the young Boobook owl below on the left. Large eyes are a prominent feature of nocturnal birds and if we were able see in the dark we would realise that their pupils are always wide open as for the adult Boobook below on the right. To me, dilated pupils look more natural and can be captured by pre-focusing and turning off the focusing light several seconds before releasing the shutter.

 

Red-eye

Red-eye occurs when the light source is located close to the camera and light is reflected from the retina into the lens. By moving the light source away from the camera or moving closer to the subject red-eye can be avoided or greatly reduced. This is shown in the diagrams 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. When red-eye cannot be avoided it can sometimes be removed by skillful photo editing, however, photos with red-eye often lack feather texture due to the flat shadowless illumination associated with a narrow flash angle.

 

Sometimes you cannot avoid red-eye as seen in the left and centre images above, however red-eye can often be 'fixed' by careful 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. Quality images can be obtained by shooting a bird leaving or arriving at a pre-focused perch or by achieving focus in flight. The Tawny frogmouth below was taken by pre-focusing on the perch it was using and by watching it with a dim red light until it flew. The Grass owl was focused in flight using a camera bracket with high intensity focus lights.

 Conclusion

My thoughts and ideas should be viewed as a guide for those interested in night photography. They should not be considered as binding, rather as ideas and techniques that have worked for me. 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 contain 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 us 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 low light 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 diagram below shows the colour sensitivity of the three types of cone cells in the human eye.

In very dim light the cone cells don't function and the brain receives signals from the rod cells only, which for nocturnal animals, enables excellent low light vision . There is only one rod type however, which means there is no perception of colour in very dim light, which is why we can't see colour outside at night even on a full moon. However, a long camera exposure in moonlight will produce an image with colours. The graph below shows the spectral sensitivity of rods in the human eye (400-600nm) and reveals why rods are completely insensitive to red light (620-680nm). The significance of this is that you can use red light for watching most nocturnal animals without spoiling their night vision or causing them excessive disturbance. Most can see red if the light is directed at them because their eyes do contain low concentrations of red senstitive cones.

 

 

White light

White light is great for finding animals but is not 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 and with the aid of a LED torch, I located it by its beautiful blue eye-shine (below). It was a Mouse deer, not much larger than a rabbit. White light can cause temporary night blindness lasting at least 10 minutes, during which time the animal could become susceptible to predation of prevent it from feeding.

 

 

Red light

Rods don't see red, so for observing animals at night, headlamps that use red LED's are ideal. 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 many more animals. Depending on the weather and where I am walking, 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 each footstep to avoid a fall.

 

About me

 

 

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 pages. 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 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 so 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 up to a dead limb, close enough for me to photograph.

 

After overcoming my fear of the dark I quickly started to enjoy 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 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 who have taught me so much about photography.

 

If you would like to use any of my images for your personal not-for-profit use such as projects etc, please reference me as the photographer. All of 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