or “Much Ballyhoo About A Molehill In A Teacup”.
I’ve been meaning to write about this one for a long time but never really got around to it until I got an e-mail from a listener asking about it. So let’s wade into the murky waters of Sensor Croppery.
This topic inspires a whole lot more confusion and argument than it really should. It’s both simple and kind of confusing simultaneously. Maybe because there are a lot of different misinterpretations floating around the web and people have dug their heels in on what they think is going on. On that note, I’ll do the same.
Keep in mind I am not a Camera Designer, nor a Sensor Engineer. Aside from the time me and a buddy created Kelly LeBrock I am not really a scientist. Weird. So what follows is MY UNDERSTANDING of what crop sensor is vs full frame.
Why The Difference?
(NOTE- Aside from mentioning it right now, we will not talk about megapixels in any of these posts. It is irrelevant to this discussion.)
Traditional 35mm film got it’s name from the fact that it is 35mm wide. Almost. In truth it is 36mm wide by 24 mm high. When the transition to digital was made that physical sensor size was mimicked. Really awesome, very expensive. But smaller sensors are cheaper so they started making those in order to make DSLRs available to more people. Different camera makers opted for different sizes (slight variables) but since I shoot Canon I’ll refer to those.
The so called “crop sensor” cameras feature a physical sensor 22.2mm by 14.8mm. These also became known as 1.6 sensors since 36/22.2 is approx 1.6. (And by extension the “true” focal length of lenses on a crop camera could be calculated by multiplying by 1.6. Thus, a 50mm lens is the equivalent of an 80mm on a full frame camera. Or is it? More on that in a later post.)
Before we dive too far into all the math involved let’s have a quick look at what is physically happening here through the use of a couple of diagrams. In the first one we see an approximation of the image your lens registers. Since your lens is circular, so is the resulting image.
The only thing is, we don’t capture the whole thing since we deal with rectangles. So when we employ a full frame (36mm x 24mm) sensor we capture this portion of the image.
And when we employ a cropped sensor (22.2mm x 14.8mm on the Canon) we capture this much of the image.
As you can see the smaller sensor captures what appears to be a crop of the larger image, hence the term “Crop Sensor” or “Crop Factor”.
So, does it matter? Well that depends. Some people say it matters very much and others insist it is entirely irrelevant. Good news is that both camps are right. I’ll explore how this all affects our image making (especially DEPTH OF FIELD) in the next few posts.