Simply said, your focal length is the physical distance between your image sensor and the point where light converges inside your lens. This distance is measured in millimetres (mm), and is explicitly stated on your lens.
Your lens’ focal length determines your angle of view. As we have mentioned in our camera basics section, your angle of view determines how much of the scene in front of your camera can be seen and captured by your camera. The shorter your focal length, so the lower the number, the larger your angle of view, and the more of the scene you will be able to capture. For example, a lens with a focal length of 24mm is able to capture more of the scene compared to a lens with a focal length of 35mm.
Something that you have to keep in mind, is that for cameras with a smaller sensor, you will have to apply a focal length multiplier. For example, when we compared the full-frame sensor with an APS-C sensor in our ‘Image sensors’ article, you could see that a multiplier of 1.5x needs to be applied. Thus, a focal length of 24mm with the same multiplier applied, would turn out to be a 36mm.
The best way for you to get a better understanding of how various focal lengths work, is by making an L-shape with both your thumbs and index fingers, and align them as a rectangle in front of you. This would simulate your frame. By holding your frame in front of you with both arms stretched out, and by looking through your frame with one eye, this would simulate your longest focal length. If you bend our elbows, and bring your frame closer to your eye, you would simulate a shorter focal length.
Notice how much more of the scene you can see when you bring your frame closer to your eye? This means that your angle of view is widening. This is one of the creative elements that can really make a difference in your photos.
Now you’re slowly grasping the concept of focal length, please have a look at maximum aperture.
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