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Lenses FAQ: What Does “Magnification Ratio” Mean?

2022-11-14
5
333

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!

In this article:

What is “magnification” in photography?

What is “magnification” in photography?

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.

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.

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.

(In real life, a ladybug is much smaller. But for the sake of convenience, let’s imagine that it’s 1cm across.)

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.


Maximum magnification and macro lenses

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.


Shot at 1.4x magnification

EOS R5 + RF100mm f/2.8mm @ f/5.6, 1/100 sec, ISO 160

At 1.4x magnification on the RF100mm f/2.8mm, the vein structure of this leaf is shown in amazing detail.

Maximum magnification, closest focusing distance, and focal length: How are they related?

The relationship between maximum magnification, closest focusing distance, and focal length

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!

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.

This is because the lenses have different closest focusing distances, also known as minimum shooting distance.


Recap: Closest focusing distance and working distance

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.

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

Relationship with closest focusing distance

Maximum magnification and closest focusing distance

EOS R5 + RF600mm f/4L IS USM

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.


EOS R5 + RF100-500mm f/4.5-7.1L IS STM

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.


Know this: (Physically) closer is not always better

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.


EOS R5 + RF100mm f/2.8 IS STM

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!

Relationship with focal length

Focal length and maximum magnification

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.

RF50mm f/1.8 STM
Max. magnification: approx. 0.25x
Closest focusing distance: 30cm

RF16mm f/2.8 STM
Max. magnification: approx. 0.26x
Closest focusing distance: 13cm

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”.


This is the same flower at around 1.4x magnification. The size difference is amazing, isn’t it!


EOS R6 + RF16mm f/2.8 STM

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


Know this: Lenses with maximum magnification at the wide end

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.

How to measure the magnification ratio?

How do we measure the magnification ratio?

If you’re curious about the magnification ratio of your image, here’s how to measure it on your own.

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.

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.

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.

Summing up + List of lenses with large max. magnification ratios

Summing up

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.

Here are the maximum magnification ratios of some RF lenses with macro or close-to-macro capabilities.

Lens Max. magnification ratio Closest focusing distance
RF14-35mm f/4L IS USM 0.38x (at 35mm) 0.2m
RF15-30mm f/4.5-6.3 IS STM 0.52x (at 15mm, during MF) 0.128m (at 15mm, during MF)
RF24mm f/1.8 Macro IS STM 0.5x 0.14m
RF24-105mm f/4-7.1 IS STM 0.5x (at 24mm, during MF) 0.13m (at 24mm, during MF)
RF35mm f/1.8 Macro IS STM 0.5x 0.17m
RF85mm f/2 Macro IS STM 0.5x 0.35m
RF100mm f/2.8L Macro IS USM 1.4x 0.26m
RF100-400mm f/5.6-8 IS USM 0.41x (at 400mm) 1.05m (at 400mm)

How are you going to use this new knowledge in your compositions today?

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