What is the Crop Factor?
The crop factor is common to most digital SLR cameras these days as they use smaller sensors than the more expensive cameras.
Professional cameras have a sensor the same size as a 35mm piece of film. Any old lenses that worked on film bodies, using the same mount, would still work on digital SLRs.
The problem with this is that the technology was big and expensive, putting the price of cameras up.
To fix this, camera manufacturers started building new cameras with smaller sensors that would take the old lenses, as well as new lenses designed to mimic the same focal length.
As you can see, you’re losing a lot of the image when you use a full frame lens. Let’s look at it from another angle.
A circular lens produces a circular image. Then the sensor crops this depending on its size. Full frame sensors are all the same size. Crop sensor sizes tend to vary between manufacturers. For the sake of this diagram, know that it’s not to scale.
How Much Does it Crop?
There are two main sizes of crop sensors. Those used by Nikon, Sony and Pentax, and the one that’s used by Canon.
The main difference is that Canon’s is slightly smaller and magnifies the image by 1.6 rather than 1.5.
What this means is that, if you put a 50mm lens designed for a full frame camera onto a crop sensor body, the focal length would effectively be 80mm, rather than 75mm.
These magnification differences don’t make a big difference at this end of the scale as the lenses are designed accordingly. All you need to know is which sensor you’re using. Then you can work out the crop factor when you want to buy a full frame lens.
How do I Know if I’m using a Crop Sensor?
This is pretty easy to answer. Simply ask yourself one question.
If you look for your camera body brand new at the moment, can you buy it for less that $2000?
If the answer is yes, you’re using a crop sensor. Full frame cameras are expensive. They aren’t that common when you compare them to amount of crop cameras around. If you walked into a store and paid less than $2000 for it, you’re shooting on a crop sensor.
Another great way of telling is to look at the kit lens that came with your camera.
Why Full Frame Lenses?
If you have only ever bought a prime lens, you’ll know why.
The lenses made for professional, full-frame cameras are usually a lot better quality. You can still buy high-quality lenses for crop sensor cameras. But if you really want to use the best lenses out there, you need to use full body lenses.
These lenses have been around long before digital cameras became popular. They provide us with the speed and accuracy you would expect for the price.
Prime lenses, in particular, are really only made for full frame cameras.
50mm is a great focal length when you’re using a full frame camera but that’s not so good on a crop sensor. It’s unnaturally zoomed. If you’re a Nikon user and want to buy a f/1.8 lens, I would always recommend the 35mm over the 50mm for a much more natural appearance.
The Right Lens For You
The first thing worth mentioning here is a realistic warning. If you’re going to replace your kit lens and you’re not planning on upgrading your body for a few years, buy a crop sensor lens.
The field of view that you lose in the shorter focal lengths is quite big. Have a look at the photos below for comparison.
The first photo was taken at 18mm on a crop sensor and the second was shot at 24mm on a crop sensor. If you shoot wide often, or even at all, you’re going to want to keep the extra few millimeters.
I would thoroughly recommend prime lenses no matter which body you’re using. Just have a look at my gear post for some recommendations.
They’re sharper and better quality for the price than any alternatives such as an all-in-one wide angle to telephoto.