About DSLR color infrared?

Infrared IR photography should be monochrome, and friends who have played Sony F707/F7 17 should be impressed. The generation of color infrared image mainly comes from the photography of IR+ visible light, and then the color is restored by PS. In other words, the source of color is still introduced by visible light, not IR itself.

Color infrared photography not only has the mysterious and quiet atmosphere of infrared photography, such as snow-like atmosphere and romance, but also has blue sky and some colors, thus forming a quite special image style, which can often achieve extraordinary results in ordinary scenes, and is a subject worthy of challenge. So as an ordinary photographer, how should we achieve color infrared shooting?

There is an olpf (OLPF==Optical low pass filter) in front of the DSLR image sensor. Its principle is to effectively reduce or eliminate moire fringes produced by imaging targets with different spatial frequencies by using the birefringence effect of the crystal, thus eliminating the influence of infrared rays on color reproduction and improving the color of the restored image sensor. According to this principle, since OLPF filters IR (equivalent to IR Cut Filter), it seems that DSLR cannot take infrared IR photography unless OLPF is replaced by another machine to allow IR (wavelength above 780nm) to pass through.

But things are often unexpected. I still remember that in the D70/D70s era, many color lovers had discussed why the early D70/D70s were more likely to produce moire stripes. The final conclusion is that OLPF prefers the latter in the choice between Moorish and infrared. However, with the later D70/D70s and even the later D50 greatly improving the effect of suppressing the mole, it seems that we can also make the judgment that "the later OLPF can let some and relatively more IR pass". In addition, a similar situation also occurs on DSLR such as Pentax *istDS, *istD and * ISTS2.

In the actual test, we can analyze it like this:

1. The wavelength of visible light is between 380 and 780nm, and the range above 780 nm and below 1200nm is near-infrared light that can be induced by CCD. The DSLR allows some IR to pass through.

2. So if we use HOYA R72 filter (filtering visible light below 720nm) or B+W 092 filter (filtering visible light below 650nm), plus the DSLR above, some visible light and some infrared light will pass through, making the image sensor sensitive. At this time, you can still take color+infrared photography, but the shutter will be slower (suitable for landscape photography).

3. If we change the machine, replace OLPF with a filter similar to HOYA R72 without IR cutoff function. Then, part of visible light+near infrared light will pass through, making the image sensor sensitive. At this time, the shutter can be faster (suitable for landscape photography and portrait photography).

As mentioned above, the only way to make color infrared images is to add visible light and use the principle of red and blue version exchange to restore the sky to blue. If we choose B+W 093 filter (which will remove visible light below 780nm), then only pure IR will pass, and there will be no colored part. In the early F707/F7 17/F828, if B+W 092 filter or HOYA R72 filter is used, color infrared images can be generated by post-processing.

Selection of infrared filter;

In fact, an infrared entrance filter like B+W 092 or HOYA R72, which lets some visible light pass through, was originally a disadvantage, but unexpectedly turned into an advantage, forming different applications:

1.HOYA R72 filter (retaining 720-780 nm visible light) +IR= standard color infrared.

2.B+W 092 filter (retaining 650-780nm visible light) +IR= enhancing color infrared.

So which filter is a better choice? It depends on your preference. Generally speaking, the so-called enhanced color infrared image will be brighter in red and blue with less snow after post-production, but it can get a faster shutter.

Color infrared also retains the characteristics and colors of infrared images when shooting.

Under the test of D50+HOYA R72 filter, when using ISO 400, F5.6 and-1EV for exposure compensation in sunny days, the shutter speed is usually 1- 1/20 seconds, and 1/8 seconds is an ordinary shutter. So it is feasible to shoot the scenery with a tripod. However, it should be noted that although this kind of shooting will not have any impact on autofocus, it is difficult to compose a picture, because the human eye can hardly see anything under the visible light of 720-780nm.

Finally, color infrared photography has opened up a new field, making landscape photography, even portrait photography, more changes and possibilities.