The incident meter sees the light directly (meter aimed from subject toward the camera instead of vice versa), and then the light reading and specified ISO compute the EV. you might limit the range to show only maybe f/2.8 to f/16 (which chart is half the width of f/1 to f/32). Meters for photography show the "EV reading" of the scene computed for the ISO specified, which varies, so if for a standard comparison, the term Light Value is converted to ISO 100. On this one standard EV chart. The energy E in electron-volts (eV) is equal to the voltage V in volts (V), times the electrical charge Q in coulombs (C) divided by 1.602176565×10-19: © 32 1/6 *½ 256" 1/8000 The point is, ISO certainly does affect the EV number. 640 How? Camera S mode: We set a preferred shutter speed, and the meter shows f/stop, and etc. Or look up the settings to find the EV (for the ISO that causes those settings). 1/1600 Again, the EV formula and the EV chart are NOT about any specific ISO value (and certainly NOT only about ISO 100). f/3.5 A light meter reads a higher EV reading to mean a brighter light requiring less exposure. That can at times improve search results. Hand-held incident light meters often do have a mode to meter an EV value (representing a row of equivalent settings in the chart), as an exposure for the ISO value you select. 250 Yes, there's an excellent EV performance calculator here at EV Convert. However, it is common practice for camera manufacturers to specify a certain luminance as an EV at ISO 100, as when specifying metering range or auto focus sensitivity. In the EV Chart at bottom of this page, the highest EV numbers use the least exposures. We normally don't even need to know EV number. ISO 400 will meter 2 EV higher than ISO 100 (so we move down two rows in the chart). If you're just starting your electric vehicle conversion journey, you might be saying to yourself: “You know what I need? 12 f/45 where L is the scene luminance, S is the ISO sensitivity, and K is a constant typically 12.5. BTW, in "things we need to know", if the Google search terms are actually a known phrase, like "Exposure Triangle" or "Field of View" or "Extension Tube Formulas", then add the quotes around your search phrase so Google will search for it as a combined phrase. by Andy 8800 *½ 1/2500 3" 1/20 But in the absolute sense (the EV chart), EV technically does just compute f/stop and shutter speed, but it computes with those values that were selected for the specific ISO you are using. f/36 But today, it is more usual for the light meter to have a mode to directly report the f/stop and shutter speed values to us, instead of a EV value. In normal usage, if your light meter meters bright sun to be EV 18 at ISO 800, then you look up EV 18 in the chart, which row gives the Equivalent Exposure settings for use to give a correct exposure at ISO 800. f/16 at 1/1000 second for example. Change ISO and the EV changes (different settings are required). If Auto ISO, both A and P modes try to observe a Minimum Shutter Speed setting, if possible, but can go slower if necessary for a proper exposure (so we watch first to see what we're doing). ISO 100 is a nice arbitrary standard choice, convenient maybe, and very popular but not special in any way. The camera then normally provides a metered ± indication of over or under exposure, which we can zero manually by changing settings. Any one setting combination is on only one row of the EV Chart, and those Equivalent Exposures make up that one row. If using ISO 100 and the light meters as EV 15, the correct camera settings are on the EV 15 row. The EV chart is about the numerical combinations of the shutter speed and f/stop values, and the resulting exposure at some ISO. And this separation of ISO is in fact how the actual exposure formula works too (next). Use this page to learn how to convert between hartrees and electronvolts. An absolute value of EV is quite meaningless without a specific associated ISO, because of course any camera exposure setting numbers of interest to us were determined by the ISO choice. Down the right side of the page, you'll find your car's make and model from the drop down box, then your electric motor type in the second drop down box, your batteries in the next, and so forth. To provide comparisons, A light meter just measures the intensity of a blob of light, but it has no human brain to recognize the scene situations to know which Equivalent Exposure combination is best. You can select limits to anything you may desire (and change table font size too), but the top and bottom EV extents will be rounded to the appropriate values to fit the chart, and will stop at the last rows with visible data. The chart is appropriate for any ISO. An Exposure calculator to compare EV value and stops difference for any two camera or meter exposures is on the previous page. ISO 100 is simply just another number, special only because our memory may be conditioned to think of it first. |

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