We are surrounded by electromagnetic radiation, coming from many sources – the earth, the sun, space, and so on.

A tiny part of this radiation is light, which is visible to the eye; we are blind to all the rest.

Our eyes can see the range between violet and red (via blue, green, yellow and orange), these wavelengths range from about 400nm (violet) to 700nm (red). Shorter wavelengths (with higher frequencies) are called ultra-violet (beyond violet), longer wavelengths (with lower frequencies) are called infra-red (below red). The symbol “nm” means nanometer (1 billionth of a meter, 1 millionth of a millimeter).

The heat that is transmitted from a warm body is in the infrared range, in the far area, where it cannot be detected by conventional photography – only by special cameras called thermal cameras, which will not be discussed in this article.
These waves are not directly visible to the human eye. Sometimes, if you want to light an object (such as a rock or a mineral, for example) with ultraviolet, the mineral reflects a light that is visible to the eye (green, blue, yellow, and so on).
The same applies to the discotheque for example, that is sometimes flooded with ultraviolet light, causing visible light to be reflected from peoples’ shirts.
This is shown due to quantum energy exchange – in which the ultraviolet light is substituted with a different light, but I will not discuss this either in this article.
A similar thing happens with fluorescent light bulbs. Ultraviolet light is produced within the bulb. The inside of the bulb is coated with material that absorbs ultraviolet light and transforms it to visible white light.
This is only possible if there is a high-energy source substituted to a lower energy form (the remaining energy is transformed to heat).
The reverse is not possible using passive methods.
Many animals have a wider range of vision than humans – especially nocturnal animals, and they can see what we cannot. These animals adapted to their way of living so that their vision developed differently than ours.
Since the large spectrum was discovered, humans have wished to “see” what goes on beyond the human visible range.
Many years ago, a reel of film that was sensitive to infrared light was developed. Photography is carried out through a filter that only passes the infrared light, and the photographing process becomes quite awkward using this method.
One has to point the camera toward the object before mounting the filter (obviously, the camera is placed on a tripod) and focus manually. After the picture is well composed, one has to mount the filter. From this point on, everything is practically done in the dark (one cannot see a single thing through the filter).
Older lenses had a small mark next to the focusing point mark that would be slightly shifted from the main point. The focusing ring was turned towards that point because infrared rays do not focus in the same plane as do the visible light rays.
Then one would press the shutter release and hope for the best.
Sometimes, the focus was not in place. Sometimes the exposure was wrong, but that’s what one had.
The digital world changed all of this. The simple digital P&S cameras were rather sensitive to infrared, and one could see on the back display what one was going to shoot. This significantly upgraded the ability to take pictures in infrared and lead many photographers to try this field of photography.
Almost all the first cameras were based on a CCD sensor and not on a CMOS sensor which made the job easier because CCD sensors are slightly more sensitive to infrared.
This changed with the development of the DSLR cameras that include a filter above the sensor, which hardly transferred infrared or ultraviolet light through, so life became somewhat harder.
We are interested in the infrared range that is between 700 and 1000nm, which is the most popular range in our world of photography.
The chaos begins with the names given to the filters. Each company uses different naming for its filters, which are sometimes the transfer range and sometimes not.
The most popular filters for infrared photography are:

The Wratten B89, which is similar to the B+W 092, and similar to the Hoya R72 that transfers the 680-720nm range and is dark red.

The Wratten 87, is similar to the Tiffen 87 that transfers the 740-795 range, and blocks all visible light.

The Wratten CB87, which is similar to the B+W 093 that transfers the 790-850nm range and is completely black.
There are other types too, but these are the most popular ones.
When using a filter that cuts out all visible light we will get a monochromatic picture (no color), when using a dark red light filter, some of the visible light can pass through and a certain variation in color can be obtained.
Since the sensors have a reduced sensitivity to infrared, the exposure time increases, and that might cause a problem with moving elements in the field of vision (for example, leaves on a windy day, people that move about and so on).
But what is so special in this type of photography?
One gets different relations of color variations between elements that reflect infrared and those that absorb it. For example, tree and plant foliage reflect infrared and will appear lighter than usual. The same applies to tree trunks and sea sand – they too appear lighter.
On the other hand, water (the sea or a pool) absorb the infrared light and will appear darker than usual, even the sky might appear darker.
When first looking at an infrared picture, one sees a strange “drama” of shades one is not used to seeing.
Some of Sony’s cameras for example, which enable night shooting, are very sensitive to infrared. The reason for this is that the sensor is very sensitive to infrared because for night shots, the camera uses infrared lighting. Other manufacturers also have infrared sensitive sensors.
For example, pictures taken with the Sony 717 – at different states with a totally black B+W filter 093. It is quite strange to use it for the first time: one cannot see anything through the filter but the camera display shows a picture.

When the camera is in its normal state, one obtains a picture in shades of light purple:

Model: CYBERSHOT Exposure Time: 1.6sec F Number: 2.2 Max Aperture Value: 2.0625 Focal Length: 9.7mm Exposure Program: Aperture priority Exposure Bias Value: 0 ISO Speed Ratings: 100 Metering Mode: Center Weighted Average White Balance: Manual white balance Flash: Flash did not fire Date Taken: 2005:08:20 08:52:56 Color Space: 65535

Conversion to black and white produces this result:

Model: CYBERSHOT Exposure Time: 1.6sec F Number: 2.2 Max Aperture Value: 2.0625 Focal Length: 9.7mm Exposure Program: Aperture priority Exposure Bias Value: 0 ISO Speed Ratings: 100 Metering Mode: Center Weighted Average White Balance: Manual white balance Flash: Flash did not fire Date Taken: 2005:08:20 08:52:56 Color Space: 65535

 

The exposure time is very long – over 1 second in full daylight!

On the other hand, when activating the night photography mechanism, the exposure time decreases significantly to 1/60^th of a second and the picture appears in slight greenish shades. Transformation to black and white produces the following picture:

The two light patches that appear on the upper part of the frame are caused by infrared lighting, which is activated at this state by LEDs that are located around the lens and the filter’s reflection is seen on the upper part of the picture.

And here are samples taken with the Nikon D100 with the same filter (B+W 093). The long exposure – 1/6^th of-a-second results in a violet shaded picture:

Model: NIKON D100 Exposure Time: 1/6sec F Number: 4 Max Aperture Value: 4 Focal Length: 12mm Exposure Program: Aperture priority Exposure Bias Value: 0.6666667 Metering Mode: Pattern White Balance: Auto white balance Flash: Flash did not fire Focal Length In 35mm Film: 18 Date Taken: 2003:08:07 17:52:14 Color Space: 65535

 

After transformation to black and white and treatment of the contrast – the following picture is obtained:

Model: NIKON D100 Exposure Time: 1/6sec F Number: 4 Max Aperture Value: 4 Focal Length: 12mm Exposure Program: Aperture priority Exposure Bias Value: 0.6666667 Metering Mode: Pattern White Balance: Auto white balance Flash: Flash did not fire Focal Length In 35mm Film: 18 Date Taken: 2003:08:07 17:52:14 Color Space: 65535

 

Notice the white foliage, the dark skies, and even the cat on the staircase that did not change its colors….

As mentioned above, all the pictures where taken with the black filter – the 093 that does not transfer even a fragment of light, which is why everything appears monochromatic.
On the other hand, if we take a step backward, and let some of the visible light enter (dark red), we can obtain strange pictures that seem as if they were taken from another world (after slightly touching them up with a computer) as with the following picture:

Model: NIKON D100 Exposure Time: 1/30sec F Number: 3.2 Max Aperture Value: 3 Focal Length: 17mm Exposure Program: Aperture priority Exposure Bias Value: 0 Metering Mode: Center Weighted Average White Balance: Auto white balance Flash: Flash did not fire Focal Length In 35mm Film: 25 Date Taken: 2005:11:25 09:53:09 Color Space: 65535

 

But we will discuss this in the following chapter!