What is the focal length conversion ratio (or crop factor) on a digital SLR?
Unless it’s a very expensive full-frame model, all digital SLRs will have a focal length conversion (also called a field-of-view crop factor) to deal with. Basically you have to re-train your mind to think in digital SLR, rather than 35mm terms. Let’s imagine this scenario. You grab your old Canon Rebel film camera and take a picture with an 18mm lens. The picture comes out like so: What an 18mm lens looks like on a 35mm camera Now move that same lens over to the Digital Rebel. Due to the difference in size between the CMOS sensor in the Digital Rebel and 35mm film (that the film Rebel uses), the digital camera captures a smaller area using that same lens than on the film camera: What an 18mm lens looks like on a D-SLR (such as the Digital Rebel) Thus, the image is cropped in the center of the frame. The 18mm lens on the Digital Rebel has the same field-of-view as a 28.8 mm lens on the film Rebel (1.6X conversion ratio).
Unless it’s a very expensive full-frame model, all digital SLRs will have a focal length conversion (also called a field-of-view crop factor) to deal with. Basically you have to re-train your mind to think in digital SLR, rather than 35mm terms. Let’s imagine this scenario. You grab your old Canon Rebel film camera and take a picture with an 18mm lens. The picture comes out like so: What an 18mm lens looks like on a 35mm camera Now move that same lens over to the Digital Rebel. Due to the difference in size between the CMOS sensor in the Digital Rebel and 35mm film (that the film Rebel uses), the digital camera captures a smaller area using that same lens than on the film camera: What an 18mm lens looks like on a D-SLR (such as the Digital Rebel) Thus, the image is cropped in the center of the frame. The 18mm lens on the Digital Rebel has the same field-of-view as a 28.8 mm lens on the film Rebel (1.6X conversion ratio). That means that a lens that was wide-angle on your film camera is
