Night vision is probably one of the best things that the wars of the 20th century left in the world. Night vision devices were originally developed during the war. Night vision optics were used by the military to spy on and survey the movement of their enemies in the dark. However, as the years pile on, the usage of night vision devices has expanded away from a piece of warfare equipment to wildlife observation, camping, hunting, and even home defense.
Night Vision lenses
One of the main working parts of a night vision device is the lenses. In fact, the lenses are the main part of the device. The two lenses found on a night vision device are:
- Objective lens:they pick up an image in the form of a reflective light or an infrared ray then focus the image on the photocathode of the image intensifier.
- Ocular lens:also known as the eyepiece. The ocular lens is the lens that displays the amplified image produced by the night vision device.
Classifications of objective lenses
Objective lenses are generally classified into four groups based on their diameter. It is important to know that the higher the diameter, the higher the amount of light the objective lens can channel into the image intensifier tube. The types of objective lenses are:
- Compact-sized objective lenses: their diameter ranges from 25mm to 28mm
- Mid-sized objective lenses: their diameter ranges from 30mm to 38mm
- Full-sized objective lenses: their diameter ranges from 40mm to 42mm
- Largest-sized objective lenses: they have a diameter that is greater than 50mm
Cleaning the objective lenses
The objective lenses of night vision equipment are usually coated with a special coating that protects the objective lens from losing its working power. This is why the objective lens of night vision equipment can not be cleaned the same way other optic devices are cleaned. Once these coatings are destroyed or they wear off the objective lens is left guard-less and very vulnerable to easy destruction. For example, the scratch-resistant coating protects the lens from scratches. Scratching on the lens can reduce the quality of the image or even provide a false detail on the image produced by a night vision device.
Also, it is important to know that the objective lens should ever be cleaned with the bare fingers as the coil on the body can dissolve the coatings. There are specially designed kits for cleaning the objective lenses but in situations where there are not available. A soft and clean cloth can be used with alcohol or distilled water to clean the lenses. Mineral and chemical water should not be used because they might dissolve the coatings.
Types of objective lens’ coating
The coatings on the objective lens perform different functions based on their type. There are three main types of coating for the objective lens. They are:
- Scratch-resistant coating: this prevents the surface of the lens from scratches.
- Anti-reflective coating: this is a special type of coating that prevents the device from excess light. It is also known as an anti-glare coating. It eliminates the internal reflection of oncoming lights from headlights and streetlights.
- Anti-fog coating: glasses are very prone to fogging-up during the cold seasons. This is why an anti-fog coating is very important.
How night vision lenses work
Night vision devices are divided into three types based on the type of information that their lens picks and interpret. They are:
- Image intensifier night vision:in an image intensifier night vision device, the objective lens of the device picks up an image in the form of reflected light. They require a very little amount of light
- Digital night vision devices:they use SMOS or CCD sensors that are similar to those used for normal digital cameras. They are less resistant to damage by bright lights, less fragile, and less expensive compared to the other two types.
- Thermal imagers:thermal imager senses the heat produced by a body. Unlike image intensifiers that uses light rays. Thermal imagers pick up infrared radiation from a body; this is then interpreted by the other components of a night vision device to produce an image of the object. Thermal imagers work perfectly even in places where there is no light.
Hybrid Thermal/Night Vision device
To go beyond the current third-generation night vision device. Some night vision manufacturers are developing a device that incorporates the intensifier technology with that of the thermal imagers. This is done in a bid to combine or have both a thermal image viewing with a night vision view on the same device.
