| Joined: | Sun Apr 1st, 2012 |
| Location: | Carthew, Cornwall, United Kingdom |
| Posts: | 6827 |
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If you use a reflected meter reading e.g. TTL then your camera will see a large black area with two small areas that are lighter. If you use Nikon matrix metering it does some clever metering so we will assume instead it is a dumb meter.
So the meter sees the black ground mostly and thinks that correct exposure for this is for a mid-grey (Kodak Grey card or 18% grey card) so it gives say 1/15 at f8 for your ISO200 setting. However in reality it is a black background which is about 3-4 stops less exposure! So your exposure should be (3stops less) so 1/125 @f8 with ISO200.
Now swap the black background for a white one. The meter sees it as a mid-grey again, not white (3-4stops more exposure is required), so gives you an reading of 1/1000 @f8 with ISO200. But the correct reading is 1/125@f8 with ISO200.
Now swap the background for a mid-grey one. The meter sees a mid-grey again, so gives you a reading of 1/125@f8 with ISO200.
If you had used incident metering then since the light falling on the subject is constant the correct exposure 1/125@f8 with ISO200 is always indicated, (for a mid-grey exposure) is shown whether or not the background is white, black or grey!
That is the simple story.
Then it is complicated by shiny or matt black, white grey.
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Still learning after all these years!
https://nikondslr.uk/gallery_view.php?user=2&folderid=none