Camera selection can affect the focal length (Canon)

It's not just the lens' focal length that affects how large a field of view you can achieve. Different lenses may display different image angles on different cameras. The same goes for brands and camera manufacturers.

Imagine you have the lens Canon EF 50mm f/1,8 II.

This lens has a fixed focal length of 50 mm, ie you can not zoom in or out. We will now do a test on how the choice of camera can affect the focal length.

We use in the test of three different digital system cameras.

Canon EOS 5D Mark II Canon EOS 1D Mark III Canon EOS 40D

We set up some miscellaneous things on a kitchen table, put the camera on a tripod and take some cards.

If we use the lens on your Canon EOS 5D Mark II so it gives the picture below. Note that there is a lot of air around the various objects.

If we now, without moving tripods etc, change camera to your  Canon EOS 1D Mark III we get the picture below. Now one of the dachshund's rear wheels has cut slightly and the air above the clown has shrunk.

If we now, without moving tripods etc, change camera to yours Canon EOS 40D we get the picture below. The air around the various motifs is now completely gone and both the dachshund and the clown have been cut.

By changing the camera, we got the same effect as if we had zoomed in on a lens, a little for each camera change.

Since the lens we used was a fixed optics, without the possibility of zooming back or forth, we wonder - how could it be that we got three different results with three different cameras?

The size of the camera's sensor affects the camera's field of view through the lens

Each digital system camera has an image sensor that digitally detects the image and the flow of light traveling through the lens into the camera. In the older, non-digital, the cameras were, for example, 35 mm film and the digital sensor today fulfills the same function.

The images above could differ depending on how large the digital camera's image sensor is.
An older system camera's classic 35 mm film had the dimensions 36.0 x 24.0 mm, but if you compare with e.g. Canon EOS 40D & so it has an image sensor that measures 22.2 x 14.8 mm. The sensor in the digital system camera Canon EOS 40D has a size equivalent to 60% of its analog predecessor.

Most lenses on the market are adapted for use with both older film cameras and newer digital cameras. Although the lens in its shape is round, it has a rectangular work surface inside. As you can see below, our three different cameras have different sized sensors, all marked in red below. These sensors should be the camera's eyes and look through the lens.

Canon EOS 5D Mark II Canon EOS 1D Mark III Canon EOS 40D

The lens is the same size all the time, of course, but when we move the lens from one camera to another, the camera is what is looking through the lens. The camera's image sensor is the eye and controls how much each camera sees through the lens.

Canon EOS 5D Mark II Canon EOS 1D Mark III Canon EOS 40D

The different sensors in the cameras thus see different amounts of the image, therefore the end result also varies. A smaller sensor sees less of the subject. From what the camera sees, the camera creates its image and the camera does not see the clown's entire hat or tail on the dachshund, well then it is not included in the image either. The images are thus cropped already inside the camera, before they are taken, if the sensor is smaller.

Canon's different sensor types

There are three different sensor types in Canon cameras and the different sensors are different sizes.

Sensor Dimensions Crop factor
FF, Full frame 36 x 24 mm  
APS-H 27.9 x 18.6 mm 1.3x
APS-C 22.2 x 14.8 mm 1.6x

Crop factor

With digital cameras, people talk about something called a crop factor or in English 'crop factor'. The crop factor indicates how much smaller the digital camera image is. In the fall Canon EOS 40D is 1.6x, because the film size of the analog camera is 60% larger than the sensor in Canon EOS 40D.

In the case Canon EOS 1D Mark III where the cropping factor is 1.3x because there it does not differ as much in the size of the sensors (about 30%).

Crop factor = Perceived focal length extension

Since we get the effect of zooming when the sensor becomes smaller, we talk about focal length extension. The image angle and focal length you get with the Canon 5D Mark II and Canon EF 50 mm f / 1.8 will be basically the same as you get with the Canon 40D and Canon 28mm f / 1.8 USM, because you then multiply 28 by 1.6 and gets 45 mm.

Below you can see the focal length extension that applies to these three camera models, which represent Canon's different sensor types.

Canon EOS 5D Mark II Canon EOS 1D Mark III Canon EOS 40D
FF , Full frame APS-H sensor APS-C sensor
No focal length extension Focal length extension 1.3x Focal length extension 1.6x

Why is all this important to me? How does it affect me in practice?

As we talked about earlier, by changing the camera, we got the same effect as zooming. With different cameras, we got a perceived change in focal length. Therefore, the focal length of an objective is not always what it appears to be. A lens and a focal length of 50 mm can suddenly become 65 mm or 80 mm, depending on the camera used.

If in the past you had a Canon analog camera and a wide-angle lens, this lens may not be experienced in the same way when you then use the lens on your newly purchased Canon digital camera. The wide viewing angle may be perceived as narrower and this is not because the lens' properties have changed, but because the cameras work in different ways. You must therefore be aware and prepared for the effect of the choice of camera on the focal length of the lens before buying a new lens or camera.

Lensora will help you

On Lensora.com, we always calculate the perceived focal length for you, so that you can see how much the perceived focal length is on your particular camera when you look closer at a lens.