How to make your own infrared perspective filter

There is no problem in making your own, as long as you can buy IR glass, but you can usually buy it in large equipment stores. There is little point in making your own~

English: IR cut filter

If you are using a film camera, you can buy special infrared film (Ilford SFX200 is a common model). Then install an infrared filter in front of the lens (filters out visible light and only passes infrared rays).

In terms of digital, I found an article:

Introduction to digital infrared photography

The basic principles of infrared photography are actually the same as those of general photography. The light is reflected on the object, passes through the lens, and forms an image in the camera. The difference is only in the difference between visible light and infrared light. Sunlight contains a rich variety of light, including infrared light. When sunlight shines on objects and is reflected into our eyes and cameras, we have actually received infrared light, but our optic nerves have not sensed it.

Principles of digital infrared photography

Cameras actually receive infrared light, but general films cannot sense it. Traditional infrared photography relies on infrared-specific films, while digital cameras use CCDs. Or CMOS itself can sense infrared, but under normal circumstances, because the amount of visible light is much greater than infrared light, the infrared effect cannot be seen (another reason is that many DCs are equipped with IR cut filters).

The function of the infrared filter (Infrared Filter) is to block visible light and allow infrared light to pass smoothly, except for the IR cut filter, which is used to block infrared rays. After adding an infrared filter in front of the lens, the film or CCD will only see infrared light. This is the simple principle of infrared photography.

Advantages of digital infrared photography

The advantages of digital infrared photography over traditional infrared photography are: traditional infrared films are expensive and troublesome to store (need to be refrigerated), and need to be developed in a specific place. The digital camera can see the results on the spot, which helps to correct parameters. It does not require two cameras to meet the needs of general/infrared photography interactive applications at the same time!

Test your camera

Generally speaking, the CCD of most digital cameras is sensitive to infrared light, but some manufacturers add an IR cut in front of the CCD in the camera filter to block infrared rays, making these cameras less sensitive to infrared rays. There is a simple way to test whether the camera is suitable for infrared photography.

Hold an infrared remote control of a general household appliance toward the camera lens and press the remote control button. At the same time, look at the camera's LCD or EVF to see if a bright light spot is visible. If the infrared light spot on the remote control is obvious, So that’s good news. (Results of shooting remote control with Olympus C-2100UZ, Photo By Steve Tang)

Purchase an infrared filter

The next step is to purchase a suitable infrared filter.

The wavelength range of visible light is approximately 400nm - 700nm. The wavelength greater than 700nm and less than 1200nm is approximately the near infrared light that CCD can sense.

The 50% cut off of the entry-level Hoya R72 or B+W 092 is just right at 720nm, but R72 can still allow part of the visible light to pass through, which is a disadvantage. Better options such as Tifeen 87 and B+W 093 infrared effect is more pure but also more expensive.

Experience

After adding the infrared filter, the brightness is greatly reduced. In my experience, I set the Olympus C-2100UZ sensitivity to 100 and use the Hoya R72 on a sunny day. Even when the aperture is opened, At the maximum (f2.8), the shutter speed is often around 1/30 second or slower.

(This situation seems to indicate that the C-2100UZ also uses an IR cut filter, and this IR cut filter blocks part of the infrared rays).

If the camera does not have an anti-shake function, a tripod is often needed! At this time, R72's shortcomings turn into advantages, because a small amount of visible light can make up for the lack of light

. If you use B+W 093, which is opaque to visible light, the problem of insufficient light will be even more serious!

About perspective

Infrared photography is often associated with perspective.

The so-called see-through is the effect produced by infrared rays passing through some substances that cannot pass visible light. The prerequisite is that there is enough infrared light, a penetrable outer layer, and an infrared filter to filter out all visible light. interference.

For example, the dark protective film on the infrared remote control becomes almost transparent when exposed to sunlight and a filter is added.

This is the reason why some of the well-known perspective photography of 0 Lux NightShot Camcoder is used.

However, perspective photography not only requires very high filters, but also the camcoder itself has the effect of amplifying weak light. Digital cameras do not

have the above-mentioned brightness-enhancing function of perspective. The effect is very limited.