Photographing without light

Monday 23 September 2019, 14:41 by Michelle Peeters | 8,939 views | 6 comments

This article was translated from Dutch with the help of AI. Read the original.

Photographing seems impossible without light. Yet you can photograph in absolute darkness. You then have to choose the invisible parts of light, such as infrared, or even completely different parts of the spectrum, such as X-rays or radio waves.

'Ordinary light', the light you can see with your eyes, is also the light your camera captures. There is more that is possible, though not for everyone.

Photo: Aperture Vintage via Unsplash
The wavelength of visible light varies roughly between 380 and 780 nanometres. Electromagnetic radiation with shorter wavelengths includes ultraviolet, X-rays and gamma rays, while longer wavelengths include infrared, microwaves and radio waves.

Rainbow

White light, incidentally, contains all the colours of visible light. This becomes clear when it is split by a prism into the different colours, from violet to red. You can also see this phenomenon in a rainbow. With a double rainbow, you can clearly see that the colours in the outer arc appear in reverse order.

Photographing in visible light is difficult enough already, but I will not go into that here. This article focuses on photographing with other wavelengths.

A clear example of how water droplets split white light into the different shades of visible light, from violet to red

Not really photography

For some images, the term 'photography' is not really correct. You can still refer to an X-ray image as 'photography', especially when it is made using plates or film sensitive to X-rays.

But it becomes more difficult when you are talking about, for example, a PET scan, which uses gamma radiation. A gamma source emits this radiation, and detectors in a ring around the patient receive it after it has travelled through the patient. An image can be formed from the measured values, based on the differences in decay.

Other imaging techniques are also used in medicine: computed tomography (CT scan, using X-rays), isotope scans (using radioactive isotopes), MRI scans (based on magnetic resonance) and SPECT scans (Single Photon Emission Computer Tomography, using radioactively labelled substances).

Visible light is also used, for example during keyhole surgery (endoscopy), while images can also be made using sound. Think of ultrasound scans of unborn babies, for example.

The technique used obviously depends on what the doctor treating you wants to see. The associated costs will also always play a part. In short, a camera is by no means always involved when an image of your body is made.

Photo: Umanoide via Unsplash

Astronomy

Observations in visible light have long been combined with images from other parts of the spectrum. The information from the separate images complements each other, helping us learn a great deal about the origin and workings of the universe.

An image in visible light can, for example, be combined with images in ultraviolet, infrared, X-rays and /or radio waves, allowing highly complex phenomena such as quasars to be analysed. The only difference between visible light and radio waves is the wavelength, so why could you not make images with them?

The information received in radio waves does of course have to be converted into a visible image for the viewer. But assigning a colour to each radio wavelength solves that problem.

To form images, you do not need to transmit signals at the desired wavelength, as with radar. You need a receiver that is sensitive to the desired wavelength. If you want to capture the infrared light from a galaxy, you need to make sure your telescope is sensitive to it.

Photo: Guillermo Ferla via Unsplash. The Andromeda galaxy
The same applies to images made with radio telescopes. They receive the radio radiation emitted by objects in space, such as stars and galaxies.

In the Netherlands, for example, there is a radio telescope in Dwingeloo with a diameter of 25 metres. The Westerbork synthesis radio telescope consists of fourteen linked 25-metre radio telescopes, which together form the images.

Because much radiation does not pass through the Earth's atmosphere, it is a great advantage that quite a few telescopes now orbit the Earth, and the Sun. They can be used to make images in infrared and X-rays, for example. The best-known telescope is Hubble, which takes images in visible light and infrared.

The optical telescopes on Earth have now become so much better that they can compete fairly well with those in space when it comes to images in visible light.

The VST (VLT Survey Telescope) has a 2.6-metre-diameter mirror, with the 268-megapixel OmegaCAM camera attached to it. This is used to take snapshots in visible light of interesting areas that can later be studied in greater detail by the large telescopes.

Photo: Gregory Hayes via Unsplash. The Milky Way

Infrared

Infrared has become an everyday part of our lives and, unlike space photography, is well within our reach. Every household has at least a handful of remote controls for various devices that emit infrared signals.

In photography, you can also use infrared light to create different kinds of images of landscapes, for example. In the analogue era, you could simply put infrared film in your camera to capture only that part of the spectrum. The photos then look dramatically different, with white leaves and black skies.

Digital cameras are less suitable for this because most sensors have an IR filter, which prevents infrared light from being captured. Enthusiastic photographers sometimes have this filter removed so that, together with an infrared filter, they can capture only that part of the light.

If you have not had this done, the photos initially look very strange, with only a heavy red haze and deep contrasts. Using this red image as a starting point, you can create all kinds of versions in photo-editing software, making these contrasts stand out even more.

This is really a matter of taste. The image is often converted to black and white, but it does not have to be. You can also add a base colour, such as sepia.

Photo: Norbert Fulep via Unsplash

Trail camera

A trail camera is a special type of camera that uses infrared. It contains an infrared sensor that can detect movement in the area and then take a photo or video. These cameras are often used to monitor the presence of wildlife in a particular area.

A night-time image of raccoons at Lacamas Creek. Photo taken with a Wildgame camera by Tanja Thomas
The same technique is also used in security cameras. During the day, the photos are simply captured in visible light, in colour, but at night an infrared flash or light is used to capture wildlife without it noticing.

These flashes come in two types: low-glow and no-glow. Low-glow uses light with a wavelength shorter than 900 nanometres, which some animals may be able to see. No-glow flashes use light with a wavelength longer than 900 nanometres, usually 940, which is completely invisible.

The advantage of low-glow flashes is that they have a greater range, allowing you to monitor a larger area. There are also versions with white-light flashes, so ordinary visible light, but you will not make any friends with those, as they will eventually scare wildlife away.

A passing black bear, photographed in daylight this time. The quality of this daylight image looks considerably better. Photo taken with a Wildgame camera by Tanja Thomas
You often hear about photos in which no animal can be seen, or only half an animal. This is probably caused by the camera's reaction time, about 0.3 seconds. Although that seems pretty fast, the animal that triggered the camera has often already disappeared from view.

You should also avoid placing the camera too close to bushes, whose branches move in the wind. The quality of the photos during the day is often quite good, while night photos often suffer from motion blur because a passing animal moves too quickly to be captured sharply.

Personal experiences

If you have had any interesting experiences photographing without light using one of the methods above, or perhaps another method, we would love to hear about them in the comments!

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