What is infrared?
This is a brief guide for infrared Beginners. It doesn't want to be a reference guide, but just a starting point.
This note will give you just a few tips about infrared photography. I want to describe which problems and difficulties you might
meet if you decide to work in the infrared field. The following information are
only the tip of the iceberg but on the internet you can dig out more
information if you like.This guide would like to be my little contribution to Infrared Photography.
But...Let’s start from the beginning.
Light, as we perceive it, is an electromagnetic radiation. What our eyes can see is just a tiny part of the whole electromagnetic spectrum.
Ok, but what is an electromagnetic radiation?
Technically an electromagnetic radiation is a self propagating wave in space with two fundamental components: Magnetic and Electric. These components, which are in a fix angle, oscillate and propagate in one direction. The number of oscillations per second is called Frequency and it is measured in Hertz (Hz).
It is possible to calculate the length of the path made by this radiation related
to its frequency because the electromagnetic radiation moves at the speed of
the light (which in vacuum is about 300 billions of meters per hour)
If you imagine this radiation as a wave, the distance between two peaks is called
Wavelength. The relationship between frequency and wavelength is the speed of the radiation
itself. The law that correlates speed, frequency and wavelength is:
Now you understand (at least in a general way) what an electromagnetic radiation is.
Back to visible light: it is possible to fix some boundaries which are the lowest and the highest frequencies (lowest Wavelength) that the human eye can perceive. By the way, this limits are arbitrary, because as for sounds, every different person can have different sensibility.
So, the two boundaries are set to 400 nanometer (for the violet color) to 700
nanometer (for the deep red color). Some people may be able to perceive a
larger range.
But... what's beyond these two boundaries?
Over this two boundaries there is different electromagnetic radiation. A radiation that our eyes can't see. Beyond violet, there is a radiation which has higher frequency than the violet color. This radiation is called Ultraviolet. in the same way, the radiation which stands before red is called infrared.
But... Which objects emit Infrared radiation?
All. In different measure, but all objects, if illuminated by daylight, emit infrared. Hot stuff such as radiators, conductors and so on. Grass, trees and foliage, when illuminated by sun, emit a lot of infrared. Infrared is often used to detect the health of trees or forests. The higher infrared emitted, the higher is the amount of chlorophyll and the healthier is the tree.
Infrared, as mentioned above, is invisible but some devices, such as digital sensors of modern cameras or special camera films can highlight it.
At this point you might think that digital cameras "record" the whole radiation spectrum. It isn't so. The digital sensor has a definite range of perception just as our eyes. Of course, it is wider than the human range but not infinite.This wide range of perception of digital sensors is not always a good improvement to digital photography.
An example of this can be explained this way: what happens if your digital camera records all the radiation that is invisible for us? Try to imagine for a while if you could see X-rays only! You wouldn't be able to recognize your friends because you would only see their bones.
The result would be terrible!
All digital cameras must be as close as possible to reality and to the way our eyes perceive reality. For this reason, camera producers build their sensors with a special filter in front of them. The filter is called visible window filter or IR-cut (Infrared Cutter). This filter has an important role in visible photography; it eliminates all unwanted electromagnetic radiation letting only the visible radiation reach the sensor.
Results are good and photos sharp!
This filter cuts not only infrared but also Ultraviolet. It's very difficult to make a perfect filter which lets only the visible light pass and cuts all the remaining radiation. The edges of the filter are not on/off but they decrease the quantity of transmitted radiation with a curve.
The higher the slope, the better and more precise the filter. At this point, you realize that it is impossible to take Infrared photography with digital cameras. Of course, it is not completely true. The reason is because filters are not perfect, so there is always a very small quantity of infrared light which passes the filter. The better the filter, the less infrared light which passes it. But the better the filter, the higher the price of the camera...!!!
Ok, words words words, but what must I do if I want to take Infrared photography?
Well, it is simple. You have to buy an infrared filter.
This filter looks like a black glass you can't see through (obviously ... It blocks visible light!!) You have to add this filter in front of your lens and click. This filter works in the same way as the original filter inside the camera. The only difference is that the window of radiation which is allowed to pass is just Infrared radiation. It cuts from the red light up to visible and even more over, and from the deep infrared to lower frequencies.
Infrared Filters looks like this.
The glass is dark, completely opaque for visible light.
Practically, it leaves a small window in the Infrared field. The only radiation that will be
recorded from the sensor will be just infrared. Now,
you have the camera, the infrared filter and you are ready to shoot but the
situation is this: you have a filter built-in on your camera which blocks
infrared and you add a filter which blocks visible light...
The problems starts here....
Up to here, I made things easier than what they really are in reality. The quantity of infrared light that reaches the sensor is really poor. This means that the exposure time should be long enough to be recorded by sensor. It is as though you took photos at night. You need a tripod, a remote shutter control to prevent camera shocks while the shutter is opened and a lot of patience. With this configuration, exposure times can increase a lot, in some cases up to 60 or more seconds.
One big problem of digital camera is the digital noise that is produced by sensor when used in long exposures.
This noise appear in the photo as small grain of pixels that are in chaotic distribution, and typically it is a mix of red, green and blue. The size of this grain (fine or coarse) depends on the sensor. Each sensor has it own noise. The same type of sensor of the same brand has a very similar noise, but not Identical. This noise increases with exposure and with the ISO level that the camera is set to.
ISO was introduced with traditional film photography. It is also known as "Film speed". It is a number that indicates how sensitive is the film at a given light. This parameter has been determined by International Organization for Standardization (ISO). It has been kept in modern technologies and is also true for digital cameras. The ISO sets the gain of a special device, called amplifier, which increases the sensivity of the sensor. The higher the sensivity of the camera, the shorter will be the exposure time with the same light conditions. In some conditions, especially when light is poor, the exposure time can be long.
If you haven't got a tripod, your photo could be fuzzy because of the natural movement of your hands, or wind, or because you are moving. If you increase the ISO, the amplifier will increase the gain of the sensor, so you'll need a shorter shutter's time to avoid a fuzzy image.
ISO levels that are common are 100, 200, 400, 800, 1600 and 3200. The higher the ISO, the higher the noise. Each level multiplies by 2 the gain of the amplifier. If the quantity of light is 1 at ISO 100, it will be 2 at ISO 200, 4 at ISO 400, 8 at ISO 800, 16 at ISO 1600 and so on...
In these conditions, you can take infrared pictures, but...
But the quality of the pictures won't be as your everyday visible pictures. Why?
Because of all the problems explained above. Plus other considerations. With long exposure times, it is very hard to find a subject that is completely immobile. Of course buildings are. But usually they are not so interesting when shooting at them with infrared camera.
The most interesting subjects for infrared photography are trees, foliage, grass, lakes surrounded by nature and so on. All this subjects can move with a mere breeze. The results on your photo will be as blurred image or an "out of focus" image.
What about focus?
This is another good question. The auto focusing system of the camera is set for visible light, in fact all the camera systems are set up for the visible range only!
So the auto-focusing system will be inaccurate. Since the wavelength of infrared radiation is different (longer than visible) the system will fail. In infrared, the focus has to be set as if the subject was closer than in visible light. Some lenses, especially the old ones, have two different marks. Green and red marks for focus metering on the body of the lens. Green marks are usually for visible light whereas the red ones are for infrared.
To summarize, it is possible to take photos with a common camera but you need to do thousands of tests and spend a lot of time with different settings. At the end, results will be far from a perfect photo. If you really want to take good infrared pictures in an easy way, there is another choice: Modify your camera.
After all, the only problem is the filter which stands in front of sensor. If you remove it, your camera will not be blind to infrared radiation and the exposure time will be comparable to exposure time for visible shoots. Depending on the camera you own, modifying it, can be easy or not.
In some case you have to disassemble the whole camera. This means you need to be skilled at unscrewing very small screws and be able to reassemble everything without losing any screw. In some case you also need to use a tin solder. If this stuff is not for you, it is possible to buy a camera already modified or a camera that has a poor IR-cut filter. This can be a good compromise.
If you modify a camera, keep in mind you won't be able to take normal visible pictures as you were before modification. Without built-in filter, your camera will work as usual but colors and features will be different. If you remove the built-in filter, you can still use the camera in the visible range but you must add a filter in front of the lens similar to the one you took off.
In practice you restore the initial camera settings. This process could be complicated but not impossible. In both cases, if you do it by yourself or if you buy an already modified camera, you have to spend some money. You could find a modified second-hand camera on markets such as e-Bay or photography magazines.
But...Let’s start from the beginning.
Light, as we perceive it, is an electromagnetic radiation. What our eyes can see is just a tiny part of the whole electromagnetic spectrum.
Ok, but what is an electromagnetic radiation?
Technically an electromagnetic radiation is a self propagating wave in space with two fundamental components: Magnetic and Electric. These components, which are in a fix angle, oscillate and propagate in one direction. The number of oscillations per second is called Frequency and it is measured in Hertz (Hz).
S=W F
where S is speed, W is wavelength and F is frequency.
If s is constant, the higher the frequency, the lower the wavelength and vice-versa.
This speed can be different depending on the material where the radiation is
propagating. In vacuum the speed is maximum, while in other materials such as
glass, speed decreases.Now you understand (at least in a general way) what an electromagnetic radiation is.
Back to visible light: it is possible to fix some boundaries which are the lowest and the highest frequencies (lowest Wavelength) that the human eye can perceive. By the way, this limits are arbitrary, because as for sounds, every different person can have different sensibility.
|
||
| |<- 400 Nanometer | 550 Nanometer | 700 Nanometer ->| |
But... what's beyond these two boundaries?
Over this two boundaries there is different electromagnetic radiation. A radiation that our eyes can't see. Beyond violet, there is a radiation which has higher frequency than the violet color. This radiation is called Ultraviolet. in the same way, the radiation which stands before red is called infrared.
|
|
|
| <- Ultraviolet | Infrared -> |
But... Which objects emit Infrared radiation?
All. In different measure, but all objects, if illuminated by daylight, emit infrared. Hot stuff such as radiators, conductors and so on. Grass, trees and foliage, when illuminated by sun, emit a lot of infrared. Infrared is often used to detect the health of trees or forests. The higher infrared emitted, the higher is the amount of chlorophyll and the healthier is the tree.
Infrared, as mentioned above, is invisible but some devices, such as digital sensors of modern cameras or special camera films can highlight it.
At this point you might think that digital cameras "record" the whole radiation spectrum. It isn't so. The digital sensor has a definite range of perception just as our eyes. Of course, it is wider than the human range but not infinite.This wide range of perception of digital sensors is not always a good improvement to digital photography.
An example of this can be explained this way: what happens if your digital camera records all the radiation that is invisible for us? Try to imagine for a while if you could see X-rays only! You wouldn't be able to recognize your friends because you would only see their bones.
The result would be terrible!
All digital cameras must be as close as possible to reality and to the way our eyes perceive reality. For this reason, camera producers build their sensors with a special filter in front of them. The filter is called visible window filter or IR-cut (Infrared Cutter). This filter has an important role in visible photography; it eliminates all unwanted electromagnetic radiation letting only the visible radiation reach the sensor.
Results are good and photos sharp!
This filter cuts not only infrared but also Ultraviolet. It's very difficult to make a perfect filter which lets only the visible light pass and cuts all the remaining radiation. The edges of the filter are not on/off but they decrease the quantity of transmitted radiation with a curve.
The higher the slope, the better and more precise the filter. At this point, you realize that it is impossible to take Infrared photography with digital cameras. Of course, it is not completely true. The reason is because filters are not perfect, so there is always a very small quantity of infrared light which passes the filter. The better the filter, the less infrared light which passes it. But the better the filter, the higher the price of the camera...!!!
Ok, words words words, but what must I do if I want to take Infrared photography?
Well, it is simple. You have to buy an infrared filter.
This filter looks like a black glass you can't see through (obviously ... It blocks visible light!!) You have to add this filter in front of your lens and click. This filter works in the same way as the original filter inside the camera. The only difference is that the window of radiation which is allowed to pass is just Infrared radiation. It cuts from the red light up to visible and even more over, and from the deep infrared to lower frequencies.
Infrared Filters looks like this.
The glass is dark, completely opaque for visible light.
An explanation of concepts above can be rappresented with following graphs:
click to enlarge picture |
Visible Light Filter This is the standard filter for visible light. Only the visible radiation can pass the filter. Beyond upper and lower boundaries the radiation is cut. The slope of the filter can be different from filter to filter. The higher the slope, the better and more precise the filter. |
click to enlarge picture |
Near Infrared Filter Near Infrared filter shifts the range of radiation allowed to pass towards infrared. Lower boundary overlaps the upper boundary of the visible range of red. Passing radiation is composed by a part of the visible red added with a part of Infrared radiation. |
click to enlarge picture |
Infrared Filter Infrared filter shifts the range of radiation allowed to pass completely out of the visible range. Lower boundary is not overlapping the upper boundary of the visible range of red. Passing radiation is composed only by part of Infrared radiation. |
click to enlarge picture |
Visible Light Filter + Infrared Filter When standard filter and Infrared filter are mounted togheter, there is an overlapping of their effects. The result is that only a very small portion of radiation will pass the two filters. The intensity of passing radiation is dimmed a lot. |
The problems starts here....
Up to here, I made things easier than what they really are in reality. The quantity of infrared light that reaches the sensor is really poor. This means that the exposure time should be long enough to be recorded by sensor. It is as though you took photos at night. You need a tripod, a remote shutter control to prevent camera shocks while the shutter is opened and a lot of patience. With this configuration, exposure times can increase a lot, in some cases up to 60 or more seconds.
One big problem of digital camera is the digital noise that is produced by sensor when used in long exposures.
This noise appear in the photo as small grain of pixels that are in chaotic distribution, and typically it is a mix of red, green and blue. The size of this grain (fine or coarse) depends on the sensor. Each sensor has it own noise. The same type of sensor of the same brand has a very similar noise, but not Identical. This noise increases with exposure and with the ISO level that the camera is set to.
|
|
| Typical sensor's noise on dark zones of the photo at low ISO (eg. 100) | Sensor's noise on same dark zones of the photo but with higher ISO (eg. 1600) |
ISO was introduced with traditional film photography. It is also known as "Film speed". It is a number that indicates how sensitive is the film at a given light. This parameter has been determined by International Organization for Standardization (ISO). It has been kept in modern technologies and is also true for digital cameras. The ISO sets the gain of a special device, called amplifier, which increases the sensivity of the sensor. The higher the sensivity of the camera, the shorter will be the exposure time with the same light conditions. In some conditions, especially when light is poor, the exposure time can be long.
click to enlarge picture |
Light hits the sensor. Sensor splits the light in three channels (Red, Green and Blue).
Each channel is sent to its amplifier. When incoming light is poor, the signal converted by sensor is low. The task of amplifier is to increase the level of incoming signal from sensor. The higher ISO number, the higher gain of amplifier. Amplifier increases incoming signal level and is not able to separate noise from images. Besides, since the amplifiers are three, the gain for each color could be lightly different. |
If you haven't got a tripod, your photo could be fuzzy because of the natural movement of your hands, or wind, or because you are moving. If you increase the ISO, the amplifier will increase the gain of the sensor, so you'll need a shorter shutter's time to avoid a fuzzy image.
ISO levels that are common are 100, 200, 400, 800, 1600 and 3200. The higher the ISO, the higher the noise. Each level multiplies by 2 the gain of the amplifier. If the quantity of light is 1 at ISO 100, it will be 2 at ISO 200, 4 at ISO 400, 8 at ISO 800, 16 at ISO 1600 and so on...
In these conditions, you can take infrared pictures, but...
But the quality of the pictures won't be as your everyday visible pictures. Why?
Because of all the problems explained above. Plus other considerations. With long exposure times, it is very hard to find a subject that is completely immobile. Of course buildings are. But usually they are not so interesting when shooting at them with infrared camera.
The most interesting subjects for infrared photography are trees, foliage, grass, lakes surrounded by nature and so on. All this subjects can move with a mere breeze. The results on your photo will be as blurred image or an "out of focus" image.
What about focus?
This is another good question. The auto focusing system of the camera is set for visible light, in fact all the camera systems are set up for the visible range only!
So the auto-focusing system will be inaccurate. Since the wavelength of infrared radiation is different (longer than visible) the system will fail. In infrared, the focus has to be set as if the subject was closer than in visible light. Some lenses, especially the old ones, have two different marks. Green and red marks for focus metering on the body of the lens. Green marks are usually for visible light whereas the red ones are for infrared.
To summarize, it is possible to take photos with a common camera but you need to do thousands of tests and spend a lot of time with different settings. At the end, results will be far from a perfect photo. If you really want to take good infrared pictures in an easy way, there is another choice: Modify your camera.
After all, the only problem is the filter which stands in front of sensor. If you remove it, your camera will not be blind to infrared radiation and the exposure time will be comparable to exposure time for visible shoots. Depending on the camera you own, modifying it, can be easy or not.
In some case you have to disassemble the whole camera. This means you need to be skilled at unscrewing very small screws and be able to reassemble everything without losing any screw. In some case you also need to use a tin solder. If this stuff is not for you, it is possible to buy a camera already modified or a camera that has a poor IR-cut filter. This can be a good compromise.
If you modify a camera, keep in mind you won't be able to take normal visible pictures as you were before modification. Without built-in filter, your camera will work as usual but colors and features will be different. If you remove the built-in filter, you can still use the camera in the visible range but you must add a filter in front of the lens similar to the one you took off.
In practice you restore the initial camera settings. This process could be complicated but not impossible. In both cases, if you do it by yourself or if you buy an already modified camera, you have to spend some money. You could find a modified second-hand camera on markets such as e-Bay or photography magazines.