Dispelling myths on sensor size, crop factor, and depth of field

Nikon & Canon crop cameras have been out for over 15 years now. But different sized frames isn’t new to digital. Even back in the film days, we had 110, 126, 35mm, half a dozen sizes for medium format, and a few for large format. It still always amazes me how much the concept of capture size still confuses some people.

This video from photographer & YouTuber Blake Evans (aka biscuitsalive) hopes to dispel some of those myths and clear up the confusion. It does goes very in-depth into all the ins and outs of sensor size, focal length & field of view, as well as aperture & depth of field. So it may have you asking more questions than it answers!

Blake’s video doesn’t actually show any new information. It’s all been out there on the web before, but this is a good explanation of many of the principles all in one video. The video goes through some of the basic principles of how lenses, focus and depth of field work, and then how it all relates to sensor size.

He also shows some side-by-side comparison to illustrate just how you can achieve similar results on different cameras with differently sized sensors.

For me, personally, the trick to figuring everything out has always just been to approach it in a different way. I don’t care about the sensor size, and I don’t look at the focal length of a lens first, I look at its field of view relative to the size of the sensor I’m using.

Whether it’s Micro Four Thirds, 1.5x Nikon crop, 1.6x Canon crop, so-called “full frame” or one of the several sizes of medium format sensors, a given focal length will offer a different field of view on them all. So, why think in terms of focal length? I look at my scene, and say to myself “Ok, this is what I want on the left side of the shot, and that’s what I want on the right side of my shot”, then figure out what focal length gives me that field of view.

Then I look at depth of field, not aperture. Aperture’s just a number, and what it does for you is, again, relative. I don’t look at a scene and think “Right, I need to shoot f/8, how much depth of field will that give me?”. I look at the scene and figure out what I need my depth of field to be. Then taking sensor size & focal length into account, I can figure out what aperture I need to give me the depth of field I want using an app on my phone.

The above pair of screen grabs from the video are why. It just makes no sense to me to think of it in terms of focal length & aperture first. It’s like planning a trip and thinking “I have $50 worth of gas in the car, where/how far can I get on that?” vs picking a destination and then figuring out how much fuel you’ll need to get there.

I shoot Micro Four Thirds, Nikon DX, “full frame” 35mm and medium format. So, it’s always just been the easiest way for me to tackle it. Far less hassle than trying to figure out a bunch of maths in my head on the fly.

The video does get quite complex, but it’s broken down into simple and practical steps. And it’s good information to understand, even if you don’t want have to keep all the maths and technical bits in your head all the time. Because once you do understand it, properly, it’s easy for you to come up with a system that translates it into a quick method for you to remember while you’re shooting.

Eventually, you’ll just be on auto-pilot and figuring this stuff out without thinking about it at all. So, grab yourself a good drink, and watch the whole thing.

[via No Film School]