Basics

Infrared pho­tog­ra­phy records the spec­trum of the near infrared on film and / or dig­i­tal sen­sors. In order to pre­vent con­fu­sion, this is not ther­mog­ra­phy or ther­mal imag­ing, which records the ther­mal infrared range.
In the infrared pho­to­graph, spec­tral com­po­nents of the light are record­ed as in con­ven­tion­al photography.

For infrared pho­tog­ra­phy, only ana­logue cam­eras with high­ly sen­si­tive chem­i­cal film mate­r­i­al were used until the begin­ning of the nineties. A major prob­lem was that the infrared image could not be eval­u­at­ed before devel­op­ment. Even the sharp­ness could only be deter­mined by ana­log means, most­ly in the vis­i­ble light with a sub­se­quent man­u­al cor­rec­tion, since infrared light has a dif­fer­ent index of refrac­tion than vis­i­ble light. A so-called IR index was marked with a red line on the dis­tance scale on SLR cameras.

Since the intro­duc­tion of dig­i­tal pho­tog­ra­phy, infrared pho­tog­ra­phy has become much sim­pler. Many of today’s dig­i­tal cam­eras have an infrared-sen­si­tive sen­sor but a built-in infrared block­ing filter.This block­ing fil­ter is the essen­tial rea­son that not all cam­eras are infrared-sensitive.

To be able to real­ize infrared pho­tographs, the vis­i­ble light must be kept away from the sen­sor. This is real­ized with infrared pass fil­ters, referred to sim­ply as IR fil­ters. These pass fil­ters blocks the spec­trum of vis­i­ble light and allow only spec­tral regions above red to pass. Depend­ing on the type of IR fil­ter, more or less vis­i­ble red is passed through.