UV Cameras Information

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Hi-resolution camera with UV Quartz optics UV cameras are a style of video camera that have been optimized for capturing light from the ultraviolet spectrum. This is accomplished by using a UV-pass filter, which will only allow light below the visible spectrum (wavelengths less than 400 nm). UV-A light, also called near ultraviolet, has a wavelength between 320—400 nm and is most relevant to UV photography. UV wavelengths let surfaces appear in greater clarity, and often depict features which are otherwise not apparent.

UV cameras operate in a fashion similar to CCD video cameras, with the main difference being that they record UV-A light. Regular CCD sensors are capable of recording UV light. UV-B light is absorbed by most lens materials, and UV-C light is absorbed by oxygen, making them mostly unimportant. While some video cameras may utilize a UV-cut filter to remove UV light from their recording, these types of cameras employ a UV-pass filter, isolating UV from other light spectrums. These filters are always made of glass, but also tend to allows large amounts of infrared light. Special filters and techniques (e.g. lighting, hot mirror filter) can be used to limit the IR contamination of UV images.

UV pass filter example. Video credit: Orion17 / CC BY-SA 4.0

UV recording takes place via either reflected UV photography, or UV fluorescence photography. Reflected UV photography involves the direct illumination of subjects by UV sources, such as the sun. UV fluorescence technology involves the removal of visible light by filtering the light source. This 'exciter' filter should be used in conjunction with another UV-pass camera filter, and recording must be done in very dark environment.

The camera lens is one of the most critical factors in capturing UV light. To create a better illuminated subject by also capturing UV-B light, a special and expensive type of camera lens made of quartz or quartz-fluoride allows for the transmission of UV light in the 180—200 nm wavelengths. A less-expensive, but viable option would be to use older (pre-WWII), uncoated or single-coated camera lenses. These thinner lenses without optical polymers can satisfactorily transmit some low-wave UV light.

Specifications

Lens

C-mount lenses have a flange-back distance of 17.5 mm and are required for C-mount cameras. By comparison, CS-mount lenses have a flange-back distance of 12.5 mm. Because of their shorter back focal distance, CS-mount lenses cannot be used with C-mount cameras. C-mount features a diameter of 1" and a 32-thread per inch mounting thread.

CS-mount cameras can use both C-mount and CS-mount lenses; however, C-mount lenses require either a 5 mm adapter or adjustments to the CS-mount camera. Because of their shorter back focal distance, CS-mount lenses can be used only with CS-mount cameras. CS-mount features a diameter of 1" and a 32-thread per inch mounting thread.

S-mount is a smaller mounting configuration used in devices such as PC cameras and board-mounted cameras. S-mounts use a M12 x 0.5 threads.

An F-mount lens utilizes a bayonet-style mount standardized by Nikon.

Resolution

Resolution is the quality of the image when viewed. For digital cameras, resolution depends upon the number of pixels (horizontally and vertically). At a standard size, more pixels sharpen details on a photograph, but when enlarged the pixels become apparent in an effect called pixelization. This is similar to grain on film. Digital camera resolution is commonly measured in megapixels (MPx), with each mega representing one million square pixels. High-definition is regarded as a resolution of 1,280 x 720 pixels or more.

UV cameras are universally CCD cameras, and are only restricted in their resolution by the limitations of the CCD. Therefore, resolutions range from low-definition 640 x 480 to extreme definition 2048 x 2048.

Frame Rate

Measured in frames per second, this is the number of image captures. The human eye is capable of differentiating between 10 to 12 separate images per second; anything more and the rapidly changing images creates the illusion of movement. Frame rate of individual cameras is very much reliant upon the playback method and territory, or the specific application of the camera, both of which are covered in depth below.

Typical broadcast frame rate is about 30 fps, but the unique applications of UV cameras dictate frame rates from 15 to 200 fps.

Shutter Speed/Exposure

Normal exposure speeds are usually effective for typical UV recording. However, using normal lenses, a UV-pass filter, and a very long exposure time, a typically CCD will detect some UV radiation. If the operator can clear the electronic noise, a reasonable but contaminated UV image will be recorded.

Since the human iris does not dilate to guard against UV overexposure, UV camera operators should keep exposure times very small when recording in UV fluorescent situations.

Sensitivity

For UV cameras, this is the ability of the image sensor to record UV light. CCD cameras are Aerospace camera with UV detection sensor sufficiently sensitive to UV radiation, while CMOS cameras tend to be inadequate in their ability to record UV.

Playback

UV cameras record video in scientific and industrial applications, and their recordings are typically relayed to programs or monitors explicitly designed to display complementary modes of video capture. Interface feed from UV cameras by Camera Link, GigE Vision, analog wiring, USB or mini USB, and FireWire is common.

Mounting

Permanent UV camera placement in laboratory and industrial settings usually sturdy, utilitarian mounts. Certain applications may require vibration resistance and protective features. UV cameras may find temporary deployment with handheld and tripod models available. Their unique flexibility in machine vision, microscopy, inspection, and imaging results n a need for many options of camera positioning.

Features

These specifications are often optional on video cameras, but depending upon the use they will enhance video quality.

Auto-Lens: Auto-lens operation is a mode in which the lens iris automatically adjusts to maintain a predetermined level of light on the image pickup device. Cameras with auto-lens mode may also provide automatic lens focusing.

Board Mount: Camera optics are mounted directly on a printed circuit board (PCB). Often, PCBs are components of larger devices.

Cooled Sensor: Sensors are actively cooled by a Peltier element or other method. Cooling reduces "dark current" noise and improves sensitivity. Many UV cameras utilize a cooled CCD design.

Dome: Cameras are enclosed in a protective dome made from materials such as acrylic or polycarbonate. Typically, these materials are optically-corrected for accurate image capture. This can create a tamper-proof housing common for security use.

Gamma Correction: Gamma is the nonlinear relationship between the video signal level and the subsequent image element brightness. Gamma correction compensates for this nonlinearity in order to render the image true in color while providing intensity to the original object.

High Definition: High definition is a video standard that has higher picture sharpness, larger picture, more colors, and higher quality sound than regular video standards. The low-end threshold for HD video is considered 1,280 x 720 pixels.

Machine Vision Sensors: Machine vision sensors have the capability to analyze events captured by its camera, and alert operators or make decisions based on the information collected. These are also called smart cameras. If they are not uniform machines, the camera is typically linked to a computer interface via a FireWire, USB, or Ethernet connection.

Outdoor Rated: Outdoor-rated devices are designed to withstand outdoor temperature variations, rain, snow, and other weather conditions.

Pan/Tilt: These devices have integral or optional mounting features enabling side-to-side (pan) and up-and-down (tilt) controllable motion.

Progressive Scan: This is a CCD design that allows acquisition of both even and odd fields at the same time. Nearly every UV camera utilizes progressive scan. Each pixel contains information from one complete frame. This technology allows high resolution without the use of a mechanical shutter. Progressive scan cameras are used for image acquisition of rapidly moving objects and accurate dimensional measurements.

Radiation Hardened: Devices are designed to withstand high levels of radiation. These cameras can be used in nuclear facility applications, or in scientific research that will expose the device to radiation. These types of cameras almost always record in monochrome. CID cameras are commonly radiation hardened.

Underwater Rated: Devices are designed to work when completely submerged in water. This feature can be added with an aftermarket housing.

Zoom: Cameras are designed with a feature that allows the device to closely focus on distant objects. Optical zooms offer better resolution than digital zooms.

3D Recording: The camera has the capability of recording images in three distinct directional planes. This is helpful for recording the depth of an object.

Applications

UV cameras are used for machine vision, high-resolution video microscopy, corona detection, semiconductor inspection, and nondestructive testing. They also find work in astronomy, UV spectroscopy, food processing, mining, fire detection, and sterilization. Interestingly, some animals exhibit innate UV capabilities; bees, for example, detect pollen in flowers with unique UV sensitivity.