Sunset in Kruger

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The focal length of a modern zoom lens isn't something that is nice and easy to work with a lens equation to get the answer. From hyperphysics on the true zoom telephoto lens, the lens can be thought of as a few different elements: The problem is, these elements keep moving around: which makes the entire system a bit more complex to calculate for. ...


Here are some possible sources of error: Manufacturer stated focal lengths are often rounded favorably or sometimes plain exaggerated (e.g. a 200mm might well be only 190mm). Focal lengths are also stated at infinity focus, lenses change focal length when focusing (though it is more common for a lens to get wider as you focus closer not narrower). Sensor ...


You can use the guide number system (see How can I calculate the effect of non-TTL flash on exposure?), possibly in combination with your camera's meter or a separate incident flash meter. But if you have several lights, modifiers, and are trying different poses and positions, trial and error is probably actually easier and faster. As you practice, it'll ...


The ratio of subject width to distance corresponds to the ratio of sensor (or film) width to focal length. Thus, for portrait orientation, you may estimate the focal length as follows: horizontal: 24 mm · 5.0 m / 0.8 m = 150 mm vertical: 36 mm · 5.0 m / 1.2 m = 150 mm

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