Camera sensors explained
This post will demystify all the jargon surrounding sensors for you. If some of the terms like “depth of field” need more explanation, join our online beginner’s course A Year With My Camera which is free by email:
What is a camera sensor made of?
CMOS = “complementary metal–oxide–semiconductor” (more efficient, runs cooler, faster, probably what your camera has)
CCD = “charged coupled device” (older sensors)
Does sensor size matter?
Bigger sensors allow more data to be collected, work better in lower light, have a higher dynamic range and, other things being equal, produce sharper images.
Sensor sizes relative to each other - not actual size
35mm = the standard negative size from the days of film
medium format = larger sized negatives used for higher quality
APS = “advanced photo system”, a negative smaller than 35mm
full frame = a digital sensor size equivalent to the old 35mm
cropped sensor = a digital sensor smaller than full frame
APS-C = a digital sensor size equivalent to the old APS “Classic” format
APS-H = a higher definition APS digital sensor developed by Canon
micro 4/3 = a cropped sensor system used by Panasonic and Olympus named for its aspect ratio (pronounced “micro four-thirds”: most other sensors have an aspect ratio of 3:2)
What is “crop factor”?
All sensor sizes are described in relation to the “full frame” standard. If you are shooting on an APS-C sensor, your crop factor is probably 1.5 (may be 1.6). You can do the maths to find the ratio or you can just Google it. Sensors smaller than full frame will have a crop factor greater than 1, those larger than full frame less than 1.
Why does crop factor matter?
For your day-to-day shooting it doesn’t matter at all. You can use your camera all your life without knowing what the crop factor is. But if you start to read photography tutorials you will start coming across phrases like “50mm equivalent”, and if you’re very unlucky you’ll get sucked into a debate about how crop factor affects depth of field.
Crop factor and focal length
Lenses are described by their focal length, eg. "50mm”. To learn more about focal lengths read this post.
A 50mm lens on a cropped frame camera behaves differently to one on a full frame camera. It acts like something with a longer focal length would. You can find out exactly what the longer focal length is by multiplying 50mm by the crop factor:
50mm x 1.5 = 75mm
Using a lens marked 50mm on a cropped frame camera will give you images that you’d need to use a lens marked 75mm for on a full frame camera. This is described by instructors as “50mm or 75mm equivalent”.
The details don’t matter too much unless you are wondering why your photos look different to someone else’s when you think you’re using the same lens. It is worth bearing in mind it is harder to get wider angle shots with a cropped frame, and easier to get very long telephoto shots.
Crop factor and depth of field
With larger sensors the depth of field will be smaller for any given aperture (if you fill the frame frame with the subject to the same degree). This means it’s easier to get that out-of-focus background with a full frame or larger sensor.
What do the bytes and pixels mean?
MB = “megabyte”: a measure of file size (1MB = 1,024,000 bytes)
MP = “megapixel”: a measure of sensor and display size (1MP = 1,000,000 pixels)
pixel = a digital image is made up of thousands of pixels and each pixel is the smallest unit that can be assigned a colour or tonal value
resolution = the amount of information (measured in pixels) that a digital image contains, affecting how well it displays (more pixels = higher resolution = better quality image)
Which camera sensor is best?
There really isn’t a “best” sensor because you aren’t just buying a sensor: you’re buying a camera system. You need to take into account how much weight you can carry, what you like to photograph and your budget. If all other things are equal then a modern, larger sensor will give you more latitude but it’s not worth breaking the bank just to buy a full frame camera.
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