Lesson 03: APS-C and mirrorless cameras

To throw even more into the mix modern cameras fall into two main categories: cameras with mirror and mirrorless cameras. It is only the APS-C type of cameras that has mirrors. The names describe the biggest technical difference, but that difference affects everything from size and weight to autofocus, battery life, and how you see the scene.

APS-C cameras use a mirror inside the camera body. Light enters the lens → hits the mirror → is reflected up into an optical viewfinder (OVF). When you press the shutter, the mirror flips up, exposing the sensor. You see the scene directly through the lens with zero lag.

Now that I have mentioned DSLR again I want to point out that these camera houses are larger and heavier due to mirror box and prism. This gives a more robust feel, often preferred by some professionals. Mirrorless cameras are smaller, lighter, simpler internal design. As a result, they are easier to carry for travel, hiking, and everyday shooting.

When it comes to autofocus APS-C cameras uses phase‑detect AF through a dedicated AF module. This is excellent for fast action, sports or wildlife. APS-C cameras have something called "live view", that basically lets the camera function like a mirrorless. You watch the image in the back screen of the camera instead of the optical viewfinder. Using this function auto focus (AF) is slower.

On the other hand, mirrorless cameras have no mirror and no optical viewfinder. Light goes straight to the image sensor. The viewfinder (if present) is an electronic viewfinder (EVF) showing a live digital preview from the image sensor. In other words, it is a more accurate presentation on how the image is going to be like with exposure, colour, and effects. If you are inexperienced and use an optical viewfinder your images can become either entirely black or white in worst case scenarios. This is because the image sensor gets too little or too much light.

Mirrorless cameras use on‑sensor phase‑detect or hybrid AF. Advantages of this is faster and more accurate eye/face tracking, better AF in video and better AF in low light. Modern mirrorless AF is generally superior to cameras with mirror.

I mentioned above something called viewfinder, and there are basically two types: optical and digital viewfinder. A viewfinder is basically the "hole" you look through while taking pictures to see what is going on. Optical Viewfinder (only found on APS-C cameras) is in real‑time with zero lag, gives a natural look and is great in bright sunlight. If the sunlight is bright enough, you may not see anything through the back screen on your camera. The downside is that it doesn't preview exposure or colour. You do not have access to histogram or focus peaking. If you are experienced this may not be that important. Electronic Viewfinder (only found in mirrorless cameras) shows exact exposure, white balance, depth of field, but can display histogram, focus peaking, zebra stripes or real‑time effects. But it uses more battery, and some people prefer the natural look of optical. DSLR cameras have much longer battery life as the viewfinder does not consume any power. In mirrorless cameras the electronical viewfinder and sensor always are active.

When it comes to lenses APS-C cameras has a huge selection of native lenses with many affordable used options. Mirrorless cameras have newer lens ecosystems, and the lenses are often sharper, more modern designs. DSLR lenses can usually be adapted (with some limitations).

Summary table for mirrorless and DSLR cameras.