الارشيف / مصادر عالمية / Interesting Engineering

What UV Cameras Are and How They Work

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Have you ever wondered how UV cameras work? Perhaps you have never heard of the technique and would like to know more?

Then read on to find out.  

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What is a UV camera?

In short, a UV camera is a device specially designed to record images in the ultraviolet part of the electromagnetic spectrum. This part of the EM spectrum is invisible to our eyes, so any renderings of captured images are digitally converted into colors we can see. 

Such specialized photography is usually used for a number of scientific, medical, or artistic purposes. UV photographs can also reveal the deterioration of artworks or structures not observable using visible light.

UV cameras can also be employed as diagnostic medical devices to check for things like skin disorders or to look for evidence of injury.

uv camera image
A photograph with Ultraviolet (335-365nm) mapped to the blue channel, visible to the green channel (500-600nm), and infrared to the red channel (720-850nm). Source: Spigget/Wikimedia Commons

In nature, some animals, especially insects, use UV wavelengths to actually see the world. For this reason, UV cameras can be used to investigate the "invisible" markings on many plants used to attract insects. 

UV photography is also particularly useful at archaeological sites, where it can reveal artifacts or traffic patterns not otherwise obvious. The technique is also commonly used in forensic sciences and has been admissible as evidence in court since the 1930s.

Similar to medical diagnosis applications, UV can be used to reveal bruises, scars, and other evidence of healing on a person's skin that might not be obvious under visible light. 

It can also be used to photograph evidence of certain bodily fluids like seminal fluid, saliva, and urine on various surfaces. As a side note, UV light cannot, contrary to popular belief, be used to find bloodstains.

Interestingly, it was recently announced that the world's fastest UV camera has been developed at the Institut national de la recherche scientifique (INRS) in Canada. This device is able to record UV photons in real-time. 

uc camera uv cup
The fastest UV camera in the west. Source: scitechdaily

Called UV-CUP, it uses a technique called compressed ultrafast photography (CUP). It can not only capture photos rapidly but also offers an unparalleled resolution in just one click. 

"With the innovations in both hardware and software, UV-CUP has an imaging speed of 0.5 trillion frames per second. It produces videos with 1500 frames in large format." - scitechdaily

Not only that, but the spatial and temporal information is first compressed into an image and then, using a reconstruction algorithm, it is converted into a video. This technique was originally limited to visible and near-IR wavelengths only. 

How does a UV camera work?

As previously mentioned, UV cameras are able to capture images using EM radiation outside of the visible spectrum of light -- namely the UV part of it. This tends to be between wavelengths of 320 to 400 nm.

For reference, visible light ranges from around 380 nm (violet) to around 750 nm (red). Typically, the human eye can perceive ranges between 380 and 700/720 nm, which unsurprisingly, is why we call it "visible light". 

In order to adapt a camera to be able to process ultraviolet pictures, there are several ways this can be done. 

uv cameras EM spectrum
The EM spectrum. Source: Inductiveload/Wikimedia Commons

The first concerns analog or classic, film-type cameras. Here, special filters can be used to allows UV light to expose the camera's film. So long as the camera's lenses are not coated for UV protection, that is. 

Digital cameras are a different story. In order for digital cameras to process UV light, the camera first needs to be converted. 

Called full-spectrum conversion, this technique requires the digital camera's IR filter to be replaced with clear glass. This technique is very useful for many areas of photography, including astrophotography, as well as improving the tonal range in black and white photography.

When taking photographs using UV light, there are two main ways to do so: 

  • Reflected UV photography
  • UV induced fluorescence

Reflected UV photography involves illuminating a subject directly with UC emitting lamps, or by using strong natural sunlight. A special transmitting filter is usually placed in front of the camera's lens which allows UV light to pass through while absorbing, or blocking out visible and infrared light. 

Uv camera image face
Example of a portrait picture captured using UV light. Source: Spigget/Wikimedia Commons

Some common cameras used for this technique include, but are not limited to, the Nikon D70 DLSR. the Nikon D40 DLSR and the Fujifilm FinePix IS Pro DSLR. The former two can perform this function unmodified, while the latter requires the internal UV and IR filters removed first (called a full spectrum conversion). 

UV induced fluorescence photography uses the same UB illumination as reflect UV photography except that a glass barrier filter is typically applied on the lens to absorb or block UV light to enable visible radiation to pass through. 

Images are created when UV light is absorbed by the subject matter, loses some energy, and is re-emitted (reflected) as longer, lower energy wavelengths of visible light. 

 

How do you take UV photos?

While it might sound complex, taking UV pictures is a pretty simple affair in reality. You just need the right kit, as previously mentioned. 

The first thing to decide upon is whether you are going to use analog or digital cameras. Both have their pros and cons but will require different camera setups to achieve the end results. 

Digital cameras, for example, enable you to use Live View to compose and frame your shot before taking the picture.

They can also help make focussing easier and stop you from potentially damaging your eyes, too -- but beware of using the camera's viewfinder with a UV-transmitting bandpass filter.

uv camera flower
Source: blossom in the torchlight

For analog cameras, UV images need to be captured slightly differently. First, you will need to compose and focus the shot without a filter, then place the filter back in when you have your shot set up.

It is also advisable to use manual focusing when taking UV photographs using an analog camera. This will prevent needing to refocus when the lens is attached. 

One of the most important considerations in UV photography is white balance. The first shot needs to be in raw so that the photographer can recover detail and color casts if need be.

Most UV photographers also recommend using a grey card to ensure the correct white balance. This will stop or reduce any color casts that present themselves in your UV photography scene.

When it comes to light sources, natural sunlight is usually more than enough as a source of UV radiation. However, glass, to some extent, can filter out UV light.

And that, ladies and gentlemen, is a wrap.

So, now you know how a UV camera works, are you tempted to give it a go yourself?

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