Cropped Sensors Explained
You're going to hear this term getting tossed around a lot. Cropped frame refers to the frame size of the sensor. Sensors come in a few sizes, but are generally sorted into two main categories; cropped frame and full frame.
A full frame sensor is usually about 35mm wide, the same size as what most of us think of when we picture an old school film frame. A cropped frame would refer to any sensor smaller than 35mm. From there, the cropped frame can be divided into a few even smaller subcategories, since cropped frame sensors are available in a variety of sizes. The most common cropped frame size in a DSLR or mirrorless camera is APS-C.
While APS-C is the most popular crop size, as we mentioned it's certainly not the only one. Panasonic and Olympus both released a four thirds size sensor, which is about 17mm wide. The nickname 'four thirds' originated from the aspect ratio, 4:3, which differs from the traditional 3:2 aspect ratio present in most cameras. After the four thirds size, even smaller sensors exist, but they are less commonly used in DSLR cameras, and are generally reserved for smartphones.
Which sensor is right for you always depends on what you intend to do with your camera, and the photos afterwards. All sensors will take a photo, but how they perform in different conditions and the amount of space required to house them differs greatly. Smaller sensors means the camera body, and it's lenses, can be considerably smaller too. These smaller, lighter cameras are perfect for street photography, and long adventures when you don't have a lot of space for heavy gear. Larger sensors require a larger body, especially in DSLRs, but often perform better, especially in low light conditions. Larger sensors mean more surface area to capture light, thus better low light shooting performance.
You should keep lenses in mind when deciding whether to go with a full frame or cropped sensor. Due to the prevalence of cropped frame sensors, specifically APS-C, there's quite a wide variety of lenses, often at reasonable prices. That's not to say that full frame sensors don't have the same variety, they certainly do, but the lenses tend to carry a higher cost.
Both cropped frame and full frame sensors offer great performance. There are many instances that professionals use cropped frame sensors, and many using full frame; remember there are some great photographers out there shooting with iPhones. It comes down to a matter of preference, a little bit of finesse, and perhaps most importantly, what you intend to do with the image afterwards.