How do the various techniques work?

As an image sensor can perceive a larger spectral range than the human eye, it can also detect long-wave infrared rays, which are no longer visible after a certain wave length. However, due to this property of the sensors colour discoloration may arise, when the share of IR light in the daylight hits the sensor. In order to solve this problem, the share of infrared light in the daylight must be filtered out as much as possible.

Camera manufacturers have various options to do this:

1.) Use of an IR band-elimination filter with colour cameras

Colour cameras are designed for daylight and use an IR band-elimination filter to avoid the aforementioned colour discoloration (this filter limits the wave length of the light to a range of approximately 380-660 nm and is inserted between the lens and the image sensor). The filter allows visible wave lengths to pass through almost unaffected. The near-infrared region of the light spectrum, however, is completely filtered out. The result is sharper images with natural colours, more richness of detail, plasticity, contrast and finer colour grading.

2.) Use of a pivoting IR band-elimination filter

The advantages of using an IR band-elimination filter in daylight also apply to cameras with a pivoting IR band-elimination filter. In addition, they are also designed for optimum use at night, as they exploit the sensitivity of the sensor (even outside of the visible range; in the IR band that begins from approximately 760 nm), by removing the filter from the light path for night photography. This may take place automatically or can be controlled externally. The camera then switches to black and white mode, and can take high-quality black and white photos, mainly by using additional IR lighting. In some models the infrared band-elimination filter can also alternatively be regulated via the camera interface.

3.) Use of an optical low pass filter

In addition to cameras with pivoting IR band-elimination filters, there are also models that have a built-in Optical Low Pass Filter (OLPF) in front of the image sensor. This works like a band pass filter. The filter allows the incident light to pass through without loss, up to 660 nm for the visible wave-length range, and from 820 nm for the infrared range. However, in the range between 700 nm and 820 nm the filter blocks the light, in order to ensure a clean separation between visible light and IR light. Therefore, with an optical low pass filter it is also possible to use IR rays with a spectrum range of 820 to 900 nm.

Change in Day/Night cameras

Until now we have called cameras that have a pivoting IR band-elimination filter “Day/Night” models, and cameras without a pivoting filter “Colour/Black and White”. However, as manufacturers hold different views on this, we have decided to call all cameras that can take both colour and black and white photos “Day/Night” cameras, in order to be consistent.

Please refer to our data sheets for further information on the type of band-elimination filter used. This will ensure that you know everything you need to know about this important criterion.