From selecting the right lens, to getting those picture-perfect shots, read on to learn more about focal length and how it impacts photography. Most DSLR lenses will not include an "X" number for a zoom measurement. The camera’s viewfinder displays this information along with the light meter, and note how the triangle has moved all the way over to -3 EV. The larger the distance, the stronger the magnification factor of the lens. The ‘mm’ stands for millimeter, and this is the distance between your camera’s sensor, and the point of convergence in the lens. Reading the camera histogram is an important skill to learn as it gives you complete control over exposure. Numbers and Letters on Lenses What does 18-55mm mean? 18mm is wide angle, and 55mm is more zoomed. The non-technical definition of the focal length of a digital camera lens is the distance between the lens surface and the image sensor. The focal length of a lens determines what your camera can focus on, and how your images are going to turn out. Understanding focal length is key to understanding how your camera works. EV stands for Exposure Value, and technically this image is underexposed by three stops. What Is MTF Testing? Instead, the focal length will only be listed, often as part of the name of the DSLR lens. DIL (digital interchangeable lens) cameras, which are mirrorless interchangeable lens cameras (ILC), also use lenses that are listed by their focal length, rather than an X zoom number. On a standard full-frame camera body, the distance from the center to the edge of the sensor is around 21.6mm. The focal length of a lens determines what your camera can … Camera lenses explained: Focal length. When a lens is measured for a … Camera manufacturers use MTF charts to see how their lenses capture and reproduce patterns, such as repeating fine lines. This refers to the focal length of your lens. You can still use an MTF chart for a full frame lens to make a comparison to an APS-C only lens. Focal length is the distance in millimetres from the imaging surface (film or sensor) and the optical centre of the lens when it is focused at infinity. Focal length is measured in millimeters (mm), and as we mentioned, typically rated to a 35 mm equivalent. When you zoom your lens in, you’re zooming between 18mm and 55mm. The better the performance of a lens, the better it can reproduce these fine lines. If you plan on shooting with an APS-C camera for the foreseeable future, there’s a good chance that you won’t just be looking at lenses that only work on crop cameras. Read on to find out what an MTF chart is, and how to use an MTF chart to understand the optimal performance of your glass. By the end of this lesson you will know how to view your camera’s histogram and, more importantly, interpret the information it gives you so that you can make decisions about exposure. 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