Equivalency is one of those topics that not only confuses a lot of people but also turns into some pretty heated arguments. It’s why people think that a lens of one focal length “turns” into another when you put it on a camera with a differently sized sensor. It’s why your depth of field both does and doesn’t change at the same time.
The video above was made as a follow-up to a video recently published by The Slanted Lens to ask does size really matter?. Naturally, when comparing medium format, full-frame, APS-C and Micro Four Thirds cameras, each with their own unique sensor sizes, it raises a lot of questions. And it did. So, this video is designed to answer them.
Equivalency in this context is essentially what you’d need to do in order to get the same (or at least, largely comparable) shots on cameras with different sized sensors. When you change that one thing, you have to change other things, which causes other things to need to change as well.
In short, when the sensor size changes, you need to change your lens in order to get the same field of view. That, in turn, means you need to shoot at a different aperture in order to get the same depth of field relative to that field of view (relativity is important). This means you might need to change your shutter speed to bring the exposure under control. Or, change your ISO if the shutter speed is a vital factor for capturing motion blur.
But that’s about as far as I’m going to try to break things down with equivalency in this post because it’s all laid out in the video, and trying to write it would just make it sound even more complex – especially when I would have to preemptively counter every troll argument in the comments.
I shoot full-frame, 1.5x crop APS-C and Micro Four Thirds (which drops to a 2.2x crop when shooting 4K). I also shoot 35mm and medium format film in various aspect ratios. Equivalency is something that I’ve had to keep in my mind for a long time when picking one camera over another to shoot photos or video. And once you understand it, it’s pretty easy to work out in your head – even if it’s difficult to explain to somebody else.
But if you’re confused about crop factors, how they affect the field of view and depth of field, and how you can get pretty much the same exact shot on multiple cameras with different sensor sizes, have a watch. Maybe you’ll realise that for a lot of what most people shoot, sensor size should be the least of real and practical concerns.