Sensor Sizes and Focal Lengths
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Hey folks. This is our next article in our series to simplify things for newer photographers. This time I am going to tackle two subjects that are related and cause some confusion.
Sensor Size
There are many different sensor sizes but at this point in time (2022), sensor size choice is less an issue than ever before. The three most popular options are full frame, micro four thirds and APS-C.
Full frame comes from the dimensions of the film gate on 35mm film cameras, basically 36mm wide by 24mm tall. Micro four thirds was implemented by Panasonic and Olympus based on an open standard. The sensor size is 17.4mm x 13mm. This produces a diagonal measurement of roughly half that of the full frame sensor.
APS-C was first designed when it was challenging to build consistency larger sensors. Different makers use different fractional measurements, either dividing the full frame diagonal by 1.5 or 1.6 APS-C has fallen in demand in recent times but is still a perfectly viable sensor size.
When we talk about sensors, inevitably someone wants to drag you into the megapixel hole. A megapixel is simply a measurement of the number of photo receptors on a sensor. This creates the incorrect and invalid perception that more megapixels are better. Megapixel count really only starts to matter when one is talking about making really big prints.
A print has more than just a print size, it also has a proper viewing distance. As there are tons of very large prints made from very old low megapixel sensors that look terrific at proper viewing distances, you are perfectly safe not to care about megapixel counts. In general, the only people who care are professionals doing massive prints, and insecure folks who believe that more is always better. The rest of us can ignore this marketing hype and spend time finding a camera that fits our hands well and is easy to use.
A smaller sensor would imply a smaller and lighter camera and this is why micro four thirds is growing so fast. As we get older, we tend to choose lighter and more convenient over bulk and weight. For similar reasons, a company like Fujifilm started with APS-C and never changed because they believe that their sensor is an ideal midpoint between full frame and micro four thirds. You’re the buyer, you get to choose and whatever you choose is going to deliver high quality images if you the photographer do your job.
Focal Length and the More Important Angle of View
The focal length of a lens is often measured in millimetres and indicates the relative distance of the focal point in the lens to the sensor. A higher number simply means more apparent magnification. This is a linear math equation. A 100mm lens will provide about twice the magnification or one half the coverage of a 50mm lens.
Therefore if the subject is small and far away and you wish to make it appear closer you will choose a larger focal length. if your goals is to make a photograph of a wider area, such as an expansive landscape, you will choose a shorter focal length.
Thus a 24mm focal length shows more than a 50mm focal length which shows more than a 200mm focal length. It’s really that simple.
Where this gets confusing is when people try to compare focal lengths across different sensors. Some makers who do both full frame and APS-C sensors name their lenses in accordance with full frame focal lengths. This alone accounts for most of the confusion. Fortunately other makers are much clearer. Fujifilm uses the actual focal length in their measurements. Micro four thirds makers use the actual focal length in their measurements.
To make this simple, think less about focal length and more about angle of view. The diagonal angle of view is the measure of how wide an angle of the scene gets to the sensor. A large angle of view means more of the scene at a given distance. A smaller angle of view means less of the scene at a given distance. If you can get your head around this and not get caught up in the full frame equivalent nonsense, you will be both happier and less likely to get confused. Most makers will document the angle of view somewhere in their specification tables.
The Normal Lens
This is an old term, from before the industry decided that calling fixed focal length lenses primes for no good reason. A normal lens ostensibly provides an angle of view close to what the human eye sees. More correctly, it is representative of how far away or how close things look when compared to the human eye. While the math to do this is complex, we are long past this and there are plenty of good guidelines for photographers. For those using a camera with a full frame sensor, that angle of view is found in lenses of about 50mm focal length. If you are using a camera with a micro four thirds sensor, that angle of view is found in lenses of about 25mm focal length. This makes sense when we remember that the diagonal measurement of the micro four thirds sensor is about half that of a full frame sensor. If we have a camera with an APS-C sensor, that “normal” angle of view is found in lenses of about 32mm focal length, with cameras such as Canon with the 1.6 factor closer to 31 mm and cameras such as Nikon and Fujifilm with the 1.5 factor closer to 33mm. Since you will be hard pressed to easily detect a 1mm focal length difference, we can think of the 32mm focal length as a generalization for APS-C sensors.
These focal lengths are often referred to as have a full frame equivalent of some other focal length. This implies that full frame is preferred. That is not so, it is simply a reference for those who came from the days of film.
Summary
The sensor size matters less than ever now. Pick the camera that fits your hands, is easy to use and comfortable to carry around. The focal length is only really relevant in the context of whatever sensor is in your camera and its relationship to other sensor sizes does not matter at all. You look through the lens and determine if it delivers the angle of view that you desire. Zoom lenses offer different angles of view in a single lens and are often found to be more flexible for most photographers. This is proven by how popular they are. Keep your focus on your own needs and don’t worry about nonsense that doesn’t help you.
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I'm Ross Chevalier, thanks for reading, watching and listening and until next time, peace.
