Honestly what is crop factor? Why do I need to know about it, and how does it affect my photography equipment?
Crop factor is one of the most annoying and complex of all of the techy aspects to photography. It can be a small thing, until you run into it and get confused, then it slaps you in the face.
Where this all comes from
We must remember that we never stray too far from our film roots, even with our huge gains in technology, a digital SLR is still built on the same basic layout of a film SLR.
In many respects, the digital sensor of the DSLR is the same as the film of the traditional SLR. In fact a full frame sensor is called “full frame” because it is fully the size of a 35mm frame of film.
So, what does that have to do with crop?
Many DSLRs are designed with what is called a “crop sensor”. This size is called many things (APS-C, DX), but no matter the name the idea is that a smaller sized sensor “crops” into the image further. The effect is that any lens you throw on the camera will look a bit more zoomed in than it would on a full frame camera. The amount of crop is defined by the crop factor of the camera. For a canon APS-C camera (like any of the rebel line) that is 1.6, for nikon DX cameras (like the d5500 for example) that number is 1.5.
That means that a 50mm lens on a canon 70D (cropped) would effectively be an 80mm lens. 100? 160mm! (as compared to a film camera, or a full frame camera like the 5Dm4)
How about on a Nikon? On the d5500 a 50mm lens would feel like 75mm. 85mm? 127.5mm. (when compared to a Nikon D4)
Why does this happen?
It will probably not surprise anyone that a round lens actually produces a circle image … called the “image circle”. Some of the very first cameras actually created circular images, but people wanted to place their photographs in frames, to match the paintings they already had in their homes.
So, rectangular prints were created from those circular images by “cropping” into that circle. Thus creating the modern conception that a photo is a rectangle.
How does that look?
From here we can see where we would “crop” into this circle to create what we know as a modern full frame image.
Let’s look at a crop sensor
We can then take this a step further, and look at the modern “crop sensor”. This term should mean a lot more to us now, that we understand ever the “full frame” is “cropped” into the image circle.
This should give you a sense of how it feels to crop in from image circle > full frame > crop sensor.
Let’s take a look at that in practice.
Without having your hands on both a full frame and a crop body, it can be hard to see the difference. So! Let’s take a look at some examples. For this demo, I setup the 70-200 on a tripod. I used this lens, because the lens has a tripod mount, so I could leave the lens EXACTLY where it was and only change the body. This means that in each side-by-side NOTHING has been changed about the subject, the lens, or the space between them. The only thing changed was between my battered 60D, and my 5Dm3 (and back).
What does that mean for my gear?
There are benefits to a full frame camera, of course: low light capabilities, bokeh, sometimes resolution, etc. But, looking at this, we notice that there isn’t anything “less” about the cropped image, they are just closer.
So, if what you are looking for is a really wide image, then it is much harder (or just more expensive) to get that on a crop body. But, if you are looking for extra reach (to see birds, or get some extra compression out of a portrait) then the extra crop is a pretty welcome feature.
As with all things, there is trade off, and at the end of the day the answer is to find the gear that helps you make the art you see in your mind. Anyone that tells you your gear isn’t good enough is: 1) trying to sell you their old gear, or 2) covering up for the fact that they wish their work looked as good as yours.
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