The Field of View is what is equivalent on the two cameras. Tall vertical objects will still be foreshortened with angle, but will not tilt back then if the camera is level (if the camera back is perpendicular to the horizontal). What we are told about any camera can be a bit crude. This is saying that using half the focal length doubles the Field of View dimension (dimension is linear), but the new angle is Not precisely double (angles are not linear). This is easy to do when the photo editors tell you the size of the crop box that you mark. Example: The calculator initial defaults match this photo example. Larger cameras normally actually specify the W×H mm sensor size directly, which is a plus (but video formats can still be an issue). It could instead be done with trigonometry, but unless the degrees of angles are to be computed, geometry of similar triangles is the easy way. The manufacturer computed Effective Focal Length from actual sensor size and focal length, so this procedure simply reverses that same calculation, which is very valid. The tape on the floor measures 30 feet, and the calculator computes 30.07 feet (which is within 0.2%). Calculators simply MUST be told accurate focal length and sensor size numbers. But for still images, the image Exif data normally shows lens focal length, for compacts and cell phones too (and is likely about all you will ever know about the cell phone lens). 16:9 in 4:3 camera Convert to mm. If perhaps a compact, your picture may have used one of those end point focal lengths, or used another intermediate one, like 10 mm focal length, and that's the number that the scene description wants (to compute the picture). The pixels determine the percent of sensor height occupied by the Object. Cameras with interchangeable lenses generally specify all the lens and sensor numbers (or Crop Factor), accurately, even if rounded a bit. But that Equivalent focal length is Not even about your camera, it is simply a comparison to another lens that is instead used on another hypothetical 35 mm film camera (for it to then see the same Field of View that your camera sees). The calculator uses those rounded values to compute ratio numbers, and then any input errors are magnified in the external field dimension results. Then the calculators will easily do this for you if you can supply your numbers to use. ${\rm magnification} = \frac{\rm image\,distance}{\rm object\,distance}$ Assuming we know the magnification, in order to calculate distance of object we need to know distance of image in the lens. 1) Give a rule for a function that has it input the real speed of the car and its output the count on the counter each second/speed. Zoom: If the lens zooms, a complication is that actual focal length will be reported in relatively coarse steps (actual may be between steps). But to specify focal length, use only your own cameras real focal length, NEVER specify any Equivalent Focal Length of another camera. to keep from using fractions, and we have 1/20 + 1/di = 1/15. The subject should not be tilted or rotated away from frontal camera view (that shows foreshortened size). It can compute your accurate sensor size, and it may be the only manufacturers specification you can ever find for compacts and phones. However, the Exif data says this Focus distance was 3.76 meters, which is 12.33 feet (but was 30 feet when it was actually measured), so don't trust that number (especially not in zoom lenses. 1/u+1/v=1/f where u is the object distance v is the image distance f is the focal length of the lens. 5:4 4x5 camera, Numbers only. It absolutely does NOT mean THIS phone lens is 26 mm (the phone lenses vary some, but are very roughly around 4+ mm). but larger angles can still cause foreshortening of vertical dimensions. An object is 2.0 cm from a double convex lens, with a focal length of 1.5cm. You must also specify the appropriate Aspect Ratio (normally 4:3 for phones and compacts). It's the same percentage of the distant field. Some phone cameras (iPhones do, but I think Androids may not) show the Equivalent Focal Length in Exif.

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