The maximum magnification ratio is an important specification for macro photographers and photographers who want a lens that allows them to take photos of small objects. It gives us an idea of how much of the frame we can fill with a subject. On most lenses, it occurs at the closest focusing distance and longest focal length, although this depends on lens design.

Working distance: The difference between the tip of the lens and the subject. Also see: What Does “Closest Focusing Distance” Refer To?

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Semiconductor photodetectors for such long wavelengths, corresponding to very low photon energies, have to have a very small bandgap energy. Suitable materials are for example mercury cadmium telluride (HgCdTe, MCT) (suitable even well beyond 10 μm) and indium antimonide (InSb, up to ≈5.5 μm). Similarly, there are focal plane arrays based on quantum well infrared photodetectors (QWIPs). The small bandgap energy also makes them very sensitive to thermal excitation within the sensor itself. Therefore, such infrared detectors often need to be strongly cooled during operation – often to 100 kelvins or even substantially below.

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Closest focusing distance: The shortest distance that must be placed between the image sensor and the plane of focus on the subject for the lens to be able to focus. Longer focal lengths usually involve a longer closer focusing distance.

Most infrared cameras have a two-dimensional image sensor (sometimes called a focal plane array) which delivers digital data through some electronic interface, for example of USB, Camera Link or LAN type. However, some special cameras have a line sensor, i.e., only a one-dimensional image sensor; those are often used for continuous imaging of moving items e.g. in production lines and in laser scanners.

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If you’re getting a macro lens to photograph living things such as insects, there’s another reason you should pay attention to the closest focusing distance: putting your lens too close may disturb your subject and cause it to fly or run away!

Shot on the RF600mm f/4L IS USM at around its closest focusing distance of 4.2m, which also gives the maximum magnification of 0.15x. With its 1.4x maximum magnification, the RF100mm f/2.8L Macro IS USM would have been able to capture the athlete’s foot much larger in the frame, but that’s also because you can shoot physically closer: its closest focusing distance is a much shorter 0.26m.

When a lens has a maximum magnification ratio of 1:1 or 1.0x, it projects onto the image sensor an image of the object that is the same size as the object in real life. We say that this lens is capable of life-size magnification.

Step 3: Calculate the magnification ratio The magnification ratio in this image is the length of the sensor (36mm) divided by the actual size of the subject (76mm), i.e., approx. 0.47x. The coin has therefore been magnified 0.47x, close to the 0.5x maximum magnification of the lens.

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The required imaging optics do not substantially differ from those for visible cameras, since it is not difficult to find optical glasses with high transmittance in that wavelength region. Essentially, one only requires adapted anti-reflection coatings and achromatic lenses.

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Due to the smaller band gap energy of InGaAs, optimum performance in terms of dark current and noise is achieved only at low temperatures; therefore, such as sensor chips are often equipped with a thermoelectric (Peltier) cooler. Unfortunately, that substantially increases the electricity consumption, and the housing often needs to be optimized in terms of heat dissipation, e.g. with cooling fins.

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Magnification ofconvexlens

Near-infrared cameras can also provide night vision in conjunction with some infrared illumination. It can be beneficial for surveillance purposes to work only with invisible illumination light, although that might relatively easily be detected. As long as substantial exposure times are acceptable, such cameras can work with rather low infrared light levels.

For such long wavelengths, special infrared optics are required. Unfortunately, that substantially contributes to the cost of long-wavelength infrared cameras. The imaging performance of such optics is also usually not great, but that may not matter since the resolution of the required image sensors is anyway quite moderate.

Usually, a camera is just considered to be an imaging instrument. The earliest camera – the camera obscura – indeed contained a chamber, which led to the origin of that term. Modern cameras usually use a lens instead of a pinhole, but otherwise also have kind of chamber. I am not sure whether one should prohibit the use of the term camera in the case of any devices not containing such a chamber – or whether some authority has determined to do so. (It happens quite often that such details of the original instrument are not so seriously considered later on.)

One reason why telephoto macro lenses like the RF100mm f/2.8L Macro IS USM are so popular is because the lens doesn’t have to be too close to the subject to achieve the maximum magnification. Here, at the lens’ 23cm closest focusing distance, there is about 9cm from the tip of the lens to the subject—enough to work without the lens casting a shadow on the subject.

Spectral regions of special interest are the atmospheric windows at approximately 3 to 5 μm (the mid-wave infrared window, MWIR) and from 8 to 12 μm (long-wave window, LWIR). Here, atmospheric transmission is relatively high, while there is strong infrared absorption in other wavelength regions.

Infrared cameras may or may not be sensitive to visible and ultraviolet light. Often, they include an optical filter which transmits only infrared light, so that sensitivity to unwanted wavelengths is avoided.

But if that’s the case, why do super telephoto lenses have smaller maximum magnifications than shorter lenses? For example, the maximum magnification of the popular RF100mm f/2.8L Macro IS USM is 1.4x, but that of the RF600mm f/4L IS USM is just 0.15x.

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One thing that the focal length changes is how much context appears in the frame. The following two images were taken near the closest focusing distance of each lens.

You’ve probably seen it in the specifications for lenses: “maximum reproduction ratio” or “maximum magnification ratio”. What does this refer to, and why does it matter? Read on to find out!

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In photography, “magnification” is usually used to refer to the magnification ratio or reproduction ratio of a lens. It can be written as a decimal (for example, “0.5x”) or as a ratio (for example, “1:2”), but the numbers refer to the same thing: the ratio of the size of an object as projected onto the image plane (i.e., the camera’s image sensor) versus the size of the object in the real world.

Their technology with infrared optics, a special long-wavelength image sensor and a cooling arrangement makes cooled infrared cameras quite expensive, but their performance is far better than that of uncooled detectors as described in the following section. The substantial weight, electricity consumption and preparation time are of course practical disadvantages.

Such detectors may still be cooled to some extent in order to improve their noise performance, but fundamentally such cooling is not required. Often, they are temperature-stabilized, i.e., the operation temperature is kept constant, typically with a small Peltier cooler, but not at a particularly low temperature.

As the animated image below shows, anything below 1.0x magnification is actually a form of “reduction”: the image projected on the image sensor is smaller than the actual object.

Even if a telephoto lens is not a macro lens, the magnification effect of its focal length can capture very interesting close-ups of tiny things in places that are otherwise hard to reach. Some photographers call such images “telephoto macro”. This close-up of sakura flowers on a tree branch was shot at 500mm from the lens’ closest focusing distance of around 1.2m—long enough so that you don’t have to climb the tree to get close! The maximum magnification ratio of this lens is around 0.33x.

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You state a gross MISNOMER. There are NO infrared “cameras”. They are “imagers”. Camera implies that there is a chamber (camera in Italian). These imagers do not have a chamber but have a focal point array detector that converts the temperature signals electronically to a colorized map.

The maximum magnification is an important specification for macro photography, as it determines how much of the frame you can fill with a tiny subject.

For thermal imaging around or below room temperature, the near-infrared spectral range is not suitable; for that, one requires mid-infrared cameras (see below), which can register lower-energy photons.

On zoom lenses, the closest focusing and maximum magnification usually (but not always!) occurs on the long (tele) end. However, some lenses like the RF24-105mm f/4-7.1 IS STM and RF15-30mm f/4.5-6.3 IS STM are capable of maximum magnifications of around 0.5x during manual focusing at their wide-angle ends. The result is a unique effect called centre focus macro.

Anyway, many infrared imaging devices do contain some kind of chamber (I mean empty space e.g. between a kind of lens and the detector), even though it might be much smaller than in the original camera obscura. At least for the mentioned near-infrared cameras, there is no doubt that the chamber required by you exists, and in other cases there may be some space at least between a filter or protection glass and the actual sensor.. Therefore, the statement “there are no infrared cameras” is definitely wrong.

Infrared cameras are cameras which are sensitive to infrared light. Cameras for different spectral regions are available, which differ substantially in terms of performance (e.g. image resolution, responsivity and frame rate) and application areas. In the following sections, we distinguish near-infrared cameras and mid- or long-wave infrared cameras.

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The wide-angle macro effect is great for capturing close-ups of small subjects while showing more of the surrounding context.

Cooling to the order of 100 K can be done relatively easily with a Stirling cooler, which is essentially a Stirling engine driven with an electric motor. It may take a couple of minutes after switching the device on until the required operation temperature is achieved. The cooled detector must be well insulated against the environment, also for preventing the deposition of ice, and is often placed in a vacuum-sealed case. Of course, the setup is substantially more bulky and expensive compared with that of a camera having only a Peltier cooler.

Magnification ofmirror

How much a subject is magnified on the image sensor depends on factors like the focal length and shooting distance. You probably know that intuitively —after all, subjects get bigger in the frame when you move closer to them or zoom in!

Near-infrared cameras are often used for inspection purposes. For example, they are used for the inspection of semiconductor wafers, solar cells and various other industrial products, also for agricultural goods like wheat and fruit. Laser beam profilers are another example.

Many long-wavelength infrared cameras do not contain a semiconductor detector based on the internal photo effect, but rather a kind of thermal detector, which responds to a temperature increase caused by absorption of incoming infrared light. Such thermal detectors can be based on different technologies:

A lens is usually considered a macro lens if its maximum magnification ratio is at least 0.5x (or 1:2). However, it must be capable of at least life-size magnification for it to be considered a true macro lens.

Step 2: Measure the length of the image The image below was shot on the EOS R and RF24mm f/1.8 Macro IS STM near the closest focusing distance. The ruler indicates that the image is around 76mm wide. In other words, an object that is around 76mm wide in real life is projected as 36mm wide on the image sensor.

Mostly for thermal imaging (thermography) applications, mid-infrared cameras are used, which can respond to substantially longer optical wavelengths – sometimes well beyond 10 μm – as are relevant for thermal radiation. It is then possible, for example, to obtain temperature maps of buildings in order to identify locations with excessive heat losses; that must work even at winter temperatures of below 0 °C, where thermal emission is rather low. There is a range of other applications, for example involving medical diagnosis, nondestructive testing, fire detection, satellite-based weather profile monitoring, air pollution monitoring and deforestation mapping, apart from military applications like passive infrared surveillance and heat-seeking missiles.

As two lenses are around the same length, we’re essentially shooting further away from the subject on the RF50mm f/1.8 STM. However, notice that although the subject appears slightly bigger in frame (“closer”) on the 16mm lens compared to the 50mm lens, it also captures more background context. This is a unique effect that may be described as “wide-angle macro”.

Typically, infrared cameras do not provide spectral information, but only intensity values for their pixels. This is in contrast to photo cameras, for example. When colorful images from infrared cameras are presented, these usually contain false colors, which only encode intensity values. However, there are also infrared cameras for multispectral imaging or hyperspectral imaging, which typically require a more sophisticated setup, e.g. with dispersive optics and a line scanner.

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The usual type of CCD and CMOS image sensors for visible light are based on silicon, and these have some sensitivity up to optical wavelengths somewhere between 1000 nm and 1100 nm – limited by the band gap energy of silicon. Although this is already in the infrared, a real infrared camera often contains a sensor chip based on a indium gallium arsenide (InGaAs), which provides a good responsivity roughly in the wavelength region from 900 nm to 1700 nm. Compared with silicon-based sensors, these are substantially more expensive and typically provide lower resolution – often only a few hundred pixels in the horizontal and vertical direction, i.e., well below one megapixel overall.

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Step 1: Find out the dimensions of your image sensor The size of the image sensor is approximately 36mm x 24mm on a Canon full-frame camera, and approximately 22.3mm x 14.9mm on a Canon APS-C camera.