Choose the Right Lens: Medium Format vs Full Frame – Focal Length Comparison
What is a camera sensor?
A camera sensor is the recording medium in your camera. In a film camera, the recording medium is the film. In a digital camera, the recording medium is the sensor – a piece of hardware that captures light and converts it into signals that create an image. The light projected onto the sensor is known as an ‘image circle’.
The bigger the sensor, the more photosites it contains. Photosites are light-sensitive spots that record whatever image data reaches them through the lens on the camera. This means that a bigger sensor can record more image data than a smaller one, producing higher-quality images.
Simple enough, right? But it gets a little more confusing when you look at the different kinds of sensor. Can a ‘medium format’ sensor really be larger than a ‘full frame’ one? The answer is yes, and here’s why.
The terms small, medium and large format all stem from the days of analog photography. Small format referred to 35mm film, medium to any film 60mm wide, and large to 4x5-inch sheets. When digital photography arrived, the 35mm small format came to be commonly known as ‘full frame’. Why? Because a full frame camera has a sensor that is the same exact size as a full frame of 35mm film.
In digital photography, then, ‘medium format’ doesn’t refer to any one specific sensor size. But medium format sensors are the largest commercially available sensors, and so are always larger than full-frame, 35mm sensors.
There’s one more type of sensor that we haven’t mentioned yet: the crop sensor. In a crop sensor camera, the sensor is much smaller. Exactly how much smaller (known as the 'crop factor') can vary, and depends on the kind of crop sensor camera you’re using.
A common crop sensor format is APS-C, which stands for Advanced Photo System Type C. These sensors are 23.5mm x 15.5mm, much smaller than 35.9mm x 24mm full frame sensors.
Crop sensor cameras are the most affordable, and thus the most accessible to novice photographers. They’re smaller, lighter, and generate smaller image files. But with the lower price tag comes lower image quality and a much tighter focal length.
Crop factors and how to calculate them
Before we move on to equivalent focal length and how to figure out which lens to use on your full-frame camera, let’s make sure we understand crop factor.
The crop factor is a ratio that compares the size of a camera's sensor to a full-frame/35mm sensor. For example, if a camera has an APS-C sensor, it typically has a crop factor of around 1.5 or 1.6. This means that the diagonal measurement of the APS-C sensor is approximately 1.5 or 1.6 times smaller than the diagonal measurement of a full-frame sensor.
It’s also possible to calculate the crop factors of different medium format sensors. Of course, these sensors are larger than full frame/35mm sensors, so the crop factor is always less than 1. For example, the most common medium format sensor is 48mm x 36mm, with a diagonal of 60mm. This has a crop factor of 0.72.
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Calculating equivalent focal length
In photography, the term "equivalent focal length” (or equivalent focal width) is used to compare the field of view produced by a lens on a camera with a specific sensor size to the field of view produced by a lens on a camera with a different sensor size. This comparison is made by considering the crop factor or the focal length multiplier of the camera's sensor.
The focal length of a lens is a measurement of the distance between the lens and the camera's image sensor when the lens is focused at infinity. It determines the lens's magnification and angle of view. A lens with a shorter focal length will have a wider angle of view, allowing you to capture more of the scene in the frame. A lens with a longer focal length will have a narrower angle of view, resulting in a more zoomed-in image.
To determine the equivalent focal length of a lens on a camera with a particular sensor size, you multiply the actual focal length of the lens by the crop factor of the camera. For example, if you have a lens with a focal length of 50mm and you are using it on a camera with a crop factor of 1.5, the equivalent focal length would be 75mm (50mm x 1.5). This means that the lens on the APS-C camera will have a similar field of view to a 75mm lens on a full-frame camera.
Remember that the physical properties of the lens don’t change when you use it on different camera systems. Think of equivalent focal length as a way to describe how the lens's field of view appears when used with different sensor sizes. It allows you to understand and compare the coverage provided by different lenses and cameras.
Use our handy calculator
Now you understand sensors, crop factors and equivalent focal length, you should understand why you’ll need to do some calculations if you want to use your 35mm/full-frame camera to recreate a photo made using a medium format camera.
In other words, when you’re watching a photography class on Visual Education and Karl is shooting with his medium format Hasselblad, you’ll need to use a different lens on your full-frame camera to achieve the equivalent focal length.
But here’s the good news: we’ve created a handy calculator to do all the hard work for you! It’s simple: just select the lens Karl uses on his medium format camera, and the tool will show you which lens to use on your full frame/35mm.
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