APS-C cameras use a smaller sensor format. They're the most popular camera format on the planet for good reasons and we'll cover those points in a minute.
You've read about them, but it's still confusing to understand. This post will try to make it easier for you to understand what an APS-C sensor camera is, the advantages and disadvantages of using an APS-C camera, and a deeper look at why professional photographers would want to use them.
APS-C is the commonly used abbreviation for Advanced Photo System-Classic. You really don't need to remember that. The more important thing to remember is that the letter C in APS-C can be thought of as a Cropped sensor. It's a smaller cropped version of the 36mm x 24mm sensor, which is called a full frame camera sensor.
The physical dimensions of the APS-C are 25.1mm wide by 16.7 mm tall for Canon and all variations (Nikon, Sony, etc.) are a similar size. This format gives you the standard aspect ratio of 3:2, the most common width by height ratio in the world of photography.
An APS-C sensor is about 1 inch wide and about 2/3 inch high. I know what you're thinking. That's pretty small. Yes, it is, but the sensor makers can still squeeze in multiple millions of light sensitive pixels to create large high quality images. The technology that has been developed for APS-C sensors is nothing short of remarkable.
LENS SELECTION. Camera companies offer more quality lens choices for their premium line of cameras, although the full frame lenses will work on the APS-C cameras.
UPGRADING. If you start with an APS-C camera and the associated APS-C lenses, you'll have to upgrade your lenses to full sized lenses in order to fit the full frame cameras if you want to upgrade your camera. It's unlikely that you'll need to upgrade to full frame unless you become a pro photographer.
DIGITAL NOISE. Individual light-collecting pixels are generally smaller on the APS-C sensors. They're not as efficient at collecting light. In low-light situations you're more likely to see digital noise as a result.
DEPTH OF FIELD. With a larger sensor there is no crop factor. You can move closer to your subject with any give lens and intentionally get a shallow depth of field and a more pleasing out of focus background behind your subject.
FASTER. There is less data to process from the smaller sensor. Therefore, you can save images to your emmory card faster and shoot more frames in burst mode.
MEMORY STORAGE. Files are smaller. More will fit on the camera memory card and your computer hard drive.
LENS COMPATIBILITY. You can use APS-C or full frame lenses on the APS-C camera bodies.
COST. Crop sensor cameras are more affordably priced. that gives you money left over to buy another lens, a good tripod, or some other helpful camera accessory.
Yes, there are some professional photographers who shoot with APS-C sensors. Despite the tenet that you should always have the best equipment available, sometimes the top of the line gear isn't necessary to use at all.
My most recent DSLR purchase was ....you guessed it, a Canon APS-C 90D.
BURST RATE. It's easier to get faster burst rates from a smaller camera and shutter. I get 10 frames per second. My full frame 5D mark III only does 6 frames per second.
UNCROPPED VIDEO. I can shoot either 4k or 120 HD without any sensor cropping like some of the full frame DSLRs have to use.
CASH. Rather than buy another full frame, I was able to buy an APS-C "crop" camera for less than half of a new full frame sensor camera.
I really struggled with my personal situation and whether to get another full frame or another APS-C crop camera. In the end I went the cheaper route because the 90D really had everything I wanted.
I hope this post was useful to you and helped you understand more about the APS-C camera format, so that you can do what's best for your situation.
Keep shooting, keep improving!