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Why are camera lenses so big and heavy?



The mirrorless camera evolution was supposed to produce smaller, lighter camera equipment, but in reality, camera manufacturers have just taken the opportunity to make larger, better lenses. The reason lies in the physics of the lenses.

Manipulating the focal length is complicated

The focal length of a lens ̵

1; which we have previously looked at in detail – is the distance between the rear node and the focal point. For a simple convex lens, this is the distance between the lens center and the focal point. However, no camera lens is a simple convex lens. These are all "compound lenses," which are lenses made up of a combination of individual lenses called "lens elements."

Cameras have a "flange focal length", ie the distance between the lens mount and the sensor. With the DSLRs of Canon it is for example 44 mm. The problem for camera manufacturers is that manipulating the focal length is complicated and generally requires the addition of additional lens elements that make things bigger and heavier. The reason for Canon's EF 40mm lens is that it is so close to the flange focal length that only a few lenses are required.

The further you move away from the flange focal length, the larger a lens will be A 600 mm lens does not have to be 60 cm long, but not 60 cm long – which would be the case with a simple convex lens – the optical design is complicated. It's the same with an 11mm fisheye lens.

There is a small sweetspot between 24mm and 50mm that can make lenses that are not that big, but for anything else, focal length optics is a significant barrier to miniaturization.

Aperture is a hard border

Aperture is a function of the focal length. When we talk about f / 5.6, we say that the lens aperture is open to the focal length divided by 5.6. For example, a 50 mm at f / 2 has a lens iris opening of 25 mm; at f / 8 the iris is open 6.25 mm.

CONNECTED: What Is Aperture

While this is not a problem with wide-angle lenses, this quickly becomes a problem with fast telephoto lenses. Take the incredibly popular Canon 70-200 f / 2.8: At 70 mm, the lens aperture is 25 mm wide, at 200 mm it is 71.5 mm. This means that with infinitely thin materials, the minimum size of the front element of the lens is about 72 mm (in fact, it is 88.8 mm), and it is simply not possible to make it smaller.

No matter what Canon – or Nikon or Sony would like to be able to physically not produce a 200mm 1: 2.8 lens with a front element smaller than 80mm. The laws of physics will not change.

Technical developments are a question

Many old lenses were not very good. They had charm, but the autofocus was off, there was regular heavy vignetting or distortion and the image was not sharp throughout the image. Modern lenses have solved many of these problems by adding more lens elements, which of course add more height and weight.

Similarly, modern developments such as powerful image stabilization add even more weight to heavy lenses.

And let's not forget zoom lenses. A main lens is (almost) always smaller and lighter than a zoom lens that covers the same focal length, as it is much easier. Zoom lenses, as you suspect, need more lens elements and moving parts.

Physics is the Problem

The problem is that the laws of physics are a thrill.

Optics is a well-researched and complicated field. To manipulate light so that objects are closer to each other or objects appear closer, while blurring the background or keeping everything in focus, and maintaining high image quality requires only large, heavy lenses.

For the time being, the dream of professional cameras is just that: a dream.

Photo credits: lightpoet / Shuterstock, LeonRW


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