What are the infrared photography skills?

As we all know, light is a kind of electromagnetic wave, and we often use wavelength to distinguish different electromagnetic waves. The unit of wavelength is usually expressed in nm (nanometer). Generally speaking, the visible part of light is called "visible light", and its wavelength range is about 380-780nm. Things invisible to the naked eye, we are used to calling them "lines", such as infrared rays and ultraviolet rays.

spectrogram

As can be seen from the above spectrogram, near the two ends of visible light, the wavelength below 380nm is ultraviolet band, and the wavelength above 780nm is infrared band (in fact, the wavelengths of infrared and visible light overlap to some extent). According to different wavelengths, infrared rays can usually be divided into three bands: the wavelength of near infrared rays is 770 ~ 3000nm；; The wavelength of mid-infrared is 3000 ~ 30000nm；; The wavelength of far infrared is 30000 ~ 30000~ 1000000nm. The infrared photography we are talking about here actually uses a part of the near infrared band, which is about 780 ~ 1500 nm.

Second, infrared photography in the digital age

Although human eyes can't directly see infrared rays, CCD/CMOS (related link: difference between CCD and CMOS) photosensitive elements used in digital cameras (including video cameras) can sense near-infrared wavelengths. These infrared rays will interfere with the imaging of digital cameras and are regarded as harmful parts of the imaging light. For this reason, most digital camera manufacturers add low-pass filters in front of CCD/CMOS sensors to block the entry of infrared rays and improve the imaging quality. However, the low-pass filter can not completely block infrared rays, which makes it possible for digital cameras to take infrared photos.

Low pass filter in front of sensor

To achieve infrared photography, it is necessary to let infrared rays reach the sensor and prevent visible light from entering. We usually do this by installing an infrared filter (related link: color filter) on the lens. Contrary to the principle of low-pass filter, the function of infrared filter is to block visible light and allow infrared light to enter. But for some photographers, it is difficult to meet their photographic needs by adding infrared filters to the lens. Usually, they will remove the low-pass filter in front of the sensor and replace it with an infrared filter, thus becoming a professional infrared camera.

These are the original skills of infrared photography that Bian Xiao shared for you. For more information, you can pay attention to Global Ivy and share more dry goods.