Published on December 28th, 2010 | by Adam1
Crop Factor Explained
What is Crop Factor?
Something you are bound to come across when researching DSLRs is the term “Crop Factor”? The two questions you probably ask yourself immediately following are what is crop factor? And why do I care?
The good news it Crop Factor is not that hard to understand. Back in the days of film a 35mm camera used 35mm film that had dimensions of 24mm x 36mm. In the days of digital that film has been replaced by a very complicated and expensive light sensor. Sensors that measure 24mm x 36mm are said to be “Full Frame” sensors or “Full Frame” cameras. Camera manufactures have found ways to make that sensor smaller and are called “Crop” sensors, or “Crop” cameras. How much smaller is conveyed in a ratio as it compares to a full frame sensor. So a 1.6x crop sensor is 60% smaller than a full frame, while a 2.0x crop camera has a sensor that is 1/2 the size of a full frame sensor.
So what does that really mean? Even better than trying to put it into words, we can see it in a picture. To the left is an image taken with a full frame sensor, the colored lines indicate what the various size sensors would see. You can see that a crop camera captures a smaller section of the image then you would with a full frame.
Is this a good or bad thing?
Because the sensor in crop camera is only using the center portion of what the lens is seeing there are some nice advantages you can get. First is better image quality. Because of how lenses are designed the best part of an image will be in the center. As you move towards the sides and corners images tend to get softer, have more distortion, and you can sometimes have a vignette or darkening of the edges.
The next advantage is longer focal length. Again because the sensor is only using the center portion of what your lens can “see” it translates into a zooming effect. If you have a x1.6 crop sensor such as the ones found on many Canon digital SLRs your 70-200mm f/2.8L lens now behaves as a 320mm lens. Being able to get a 300+mm f/2.8 lens for the price of a 200mm one is a huge bonus. The downside to this bonus however is the zoom effect applies to both ends. Meaning your 70mm is now 112mm.
Manufacturers have responded to this “zooming effect” by offering a new type of lens specifically designed for crop cameras. Canon calls theirs EF-S lenses while Nikon refers to them as DX lens. In either case they are typically wider to compensate for the effects of the smaller sensor. Lenses such as the Canon 10-22mm would be considered almost a fisheye on a full frame camera, but on the crop camera is equates to 16-35mm or just a wide angle.
The important thing to remember with regards to these new type of lenses is that unlike their full frame counterparts they will only fit on the crop cameras. Meaning that EF-S 10-22mm you used on your Canon 7D will not fit on a Canon 5D MkII. But the “normal” Canon EF 16-35mm will fit on either camera. If you ever intend on moving from a crop camera to a full frame you may not want to invest in an entire line of EF-S or DX lenses. In the mean time having a couple can be very nice as they are the only way to get the field of view you are looking for.
Which one should you get?
This really comes down to personal choice. Crop sensor cameras are cheaper than their full frame brothers, but the full frame sensor can get you better depth of field and bokeh. Crop cameras give you a nice “zoom” boost on the long end, but can require special lenses to get a normal view on the short end. My advice is not to get too hung up on crop vs full. Both work very well and odds are you are going to be happy either way. Buy the camera that fits you and take the sensor into account same as you would frames per second, or low light performance, but don’t let it be more important then it really is.