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.

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

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.

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”.

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!

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.

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!

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.

By calculating the ratio of the intensity of the red, green, and blue light received, it is possible to distinguish differences in the colour or appearance of the object.

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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.

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.

For a white object, all three colours of red, blue, and green are reflected.* The white circle in the diagram represents a white light source.

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.

If light containing the red, blue, and green wavelengths is shown on a red object, only red light will be reflected.* The white circle in the diagram represents a white light source.

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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.

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!

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.

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

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.

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.

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.

There are two types of colour sensors. One illuminates the object with broad wavelength light and differentiates the three types of colour in the receiver. The other type illuminates the object with the three types of light (red, blue, and green) independently.In both scenarios, the received light intensity of red, blue and green are detected, and the ratio of light received is calculated.

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.

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.

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.

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.

Sensors come in a wide variety, and each type has strengths and weaknesses. This section provides a detailed look at colour sensors.

A colour sensor is a type of "photoelectric sensor" which emits light from a transmitter, and then detects the light reflected back from the detection object with a receiver.A colour sensor can detect the received light intensity for red, blue and green respectively, making it possible to determine the colour of the target object.

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