Infrared photography (part I)

Staff Blog

Infrared photography (part I)

Dec 8, 2016

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In this review I will try to consider the infrared (IR) photography using IR-filters and specialized spectral cameras. This technique is quite difficult, but we will try to explain it in the most easy way.

Contents

How it works?
Shooting options
Gears options
- IR-cut filters
- IR cameras Lenses
Practical part
- Shooting RAW-processing
- Black-and-white
- RAW-processing in the camera
- Black-and-white
- RAW-processing in photo editors
- Automated RAW-processing in Photoshop
- Manual RAW-processing in Photoshop/Lightroom
Summary

How it works?

Do you know that only a short range of light spectrum between 400-700nm could be seen by the human eyes? Light waves up to the 400nm are called ultraviolet light and the waves over the 700nm - IR-light. Both are not visible by the eyes. Thus, only the visible range of the spectrum is considered as a norm for humans.

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But sensors of the digital cameras has no such "lack" and originally able to capture a wider range of the spectrum. Therefore, the image from the "naked" sensor would have huge difference from the usual view for our eyes (with a predominance of blue and red colors). For this reason manufacturers of digital cameras set a special pre-filters, which are cutting off unnecessary light beyond the visible range. This is why shots made with usual cameras are so close to perception of our eyes.

But if we are not able to see some things it doesn’t mean it doesn't exist. And this is the essence of IR-photography. Using this technique, you can take shots that will be radically different from what we see with our eyes.

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Shooting options

In fact, this is a genre of black-and-white photography, but the brightness here will be determined not only by the amount of light, but also the physical surface temperature. For instance the water will be dark, the foliage heated by the Sun is white and so on.

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Usual image in the visible spectrum

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IR-image after deep processing (b&w version)

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IR-image after deep processing (colored version)

Since we are talking about photography, we can make time-lapse footages as well:

Invisible Vietnam from Timon on Vimeo.

Gears options

IR filters

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Despite that the cameras have built-in pre-filters cutting the IR-light, some small part of invisible IR-light still remains and reaches the sensor. Therefore, in order to "catch" only this small amount of invisible light were developed special IR-filters, which cut off all the light except IR-range. Thus sensor of the camera gets only a small amount of IR-light. Because of this you often have to shoot with a long exposures (this point will be discussed below).
Different models of IR-filters has different cutting intensity. Many of them cutting light up to the 700nm. They still transmit small range of the visible light, but are compatible with many cameras and you can shoot with rather short exposures. Much more rarely you can be seen more aggressive filters cutting light up to 800nm. They have stronger effect, but due to the different intensity level of built-in IR-cut pre-filters, could be incompatible with some camera models and you have to shoot with extra long exposures. Also such filters are quite expensive.
In Kenko filter line-up there is REALPRO R72 filter which cuts the light up to 700nm. It might be a better choice if you just trying yourself in such shooting technique.

IR cameras

Photographers who seriously envolved in IR-photography often prefer to modify the camera. There are many ways to do that and hard to say which one is the most correct.

The most versatile way is to mechanically remove built-in IR-cut pre-filter in front of the sensor. This will allow you to clean the light from all factory pre-filtering options. And after that you can freely control the light using appropriate filters in the front of the lens. This option is good by the versatility, because allow you to use camera in any spectral range, both in UV and IR (everything will depend on the filter).

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Disassembling the IR-cut pre-filter from the camera sensor

If you are interested only in IR-photography, you can go ahead in the camera modification and install the IR-filter directly on the sensor. A huge advantage of this way is that you will no longer need to use IR-filter on the lens (it will always be on the sensor).

It is important to note that this modification is quite difficult to do on your own and even a small mistake may break the camera or its functionality. Therefore, it is better to bring your camera to a specialized shop. For example, this site offers a very wide range of modifications for the spectral photography (not only for IR). Also you can buy there necessary parts and find detailed step by step guides for many cameras, if you do decide to do the modification on your own.

But the most safest way is to purchase camera that is specially designed to shoot in IR spectrum.

The apparent advantage of using the modified cameras is the ability to work with the maximum possible IR-spectrum. This allows you to shoot with faster shutter speeds and get better pictures. However, you must remember that after any of such modifications you won't be able to use the camera for ordinary photography.

Lenses

No matter which option you choose (using IR-filter with the regular camera or the camera modification), you should realize that not all lenses are suitable for IR-photography.

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The sample of unsuitable lens for IR-photography (hot spot)

In fact some lenses has specific optical scheme that cause reflections in the IRspectrum. In regular photography it is not visible, but in IR-spectrum it is expressed by the illuminated area at the center of the image, which is called the hot spot.

There is no any unified classification of the lenses compatible for IR-photography, but you can find a lists of tested lenses to certain resources. Here are few of them:

Table from http://kolarivision.com
Table from http://dpanswers.com

In any case, if there will be no information about your lens, you always can check it on your own.

To be continued...