The Very Simple Truth About Full-Frame Versus APS-C

I was afraid photography wasn’t confusing enough, but luckily, today, a video came along and made it worse.

I have been studying a lot over the last couple of months, and I have learned a lot. A lot of the facts I have learned contradict other facts I have learned, so clearly, the fact status of some facts has to be called into question. Also, I may have simply misunderstood some things.

Here is one thing I thought I understood: full-frame cameras can be used in lower light than APS-C cameras, because they gather more light. I wasn’t sure why this was true, but whatever. I’m not here to argue with settled knowledge. I just assumed it was true.

Today I saw a video in which an expert showed that if you have an APS-C camera and a full-frame camera side by side, taking the same picture in the same light, they use the same settings. You don’t have to change the exposure.

As he showed, the smaller lens is…smaller…but so is the sensor, so it gets just as much light per unit of sensor area.

If this is true, then how can big cameras do better in low light?

I did what I always do when human beings explain things badly and say things that can’t be true. I asked AI. AI was also confusing and misleading, but as I kept picking at AI’s statements, I finally saw what the issue was. I thought I would publish my conclusion here in case anyone out there is as confused as I was.

Big cameras do not produce better pictures in low light. They just produce bigger pictures of exactly the same quality. When you try to magnify an APS-C image to the same size, you get a grainier result because you are spreading the same finite signal out over a larger area.

Why don’t people just say that?

When you take a picture, your lens projects light onto your sensor. Your sensor collects data and turns it into a raw file. That’s all you get, and you can’t get any more, ever. That is your digital “negative.” If your negative is smaller, and you blow prints up to the same size as prints from a bigger negative, the prints will be grainier.

People like to say full-frame is something like 1.5 stops better in low light, and that is wrong. It makes it sound like you can open the aperture on an APS-C camera up a couple of stops and fix the grain. That does not work. It will overexpose or otherwise change the photo unless you change something else, so it’s a different photo.

In reality, you can’t catch up. If you use APS-C, you will always have more noise for photos that are the same size as full-frame photos. You shouldn’t care, however. You can still get great photos, because noise below a certain threshold is not noticeable, and because noise-reduction software can often kill enough noise to make your grainier shots look about as good as a full-frame shot can look.

So:

1. Small sensors produce photos that are just as nice as full-frame photos, but they are smaller.

2. If you want them to be just as big as full-frame photos, you will always have to blow them up, increasing noise.

3. Noise doesn’t matter if a) it’s slight or b) your software can fix your photos so well no one will ever be able to tell the noise was there.

On the whole, if I had to give up full-frame or APS-C, I would give up full-frame, because the equipment is heavy and expensive, and APS-C equipment produces excellent results. If I thought I always had to have as little noise as humanly possible, which would be a mental illness instead of a smart conclusion, I would buy a medium format camera with a giant sensor, and it would be nearly useless because it would have very few features. I don’t think anyone uses medium format unless there is no choice, and I think full-frame is usually less practical than APS-C.

This stuff shouldn’t concern most of us much. Right now, I have a phone photo above my TV, and the photo is around 26″ wide. It’s a picture of my wife and me in Hong Kong, on Victoria Peak, with the city below us in the background. It looks fantastic. Us, the buildings…everything. You can’t count our eyelashes, but why would you need to?

You don’t stare at big photos from half an inch away. You have to stand back, so whatever pixel-level problems there are will be hard or impossible to see. If I can get a beautiful 26″ print out of a phone, you can do just fine with APS-C. If you plan to keep your prints and displays small, you shouldn’t even be thinking about the full-frame edge.