View single post by jk
 Posted: Sat Mar 27th, 2021 00:57
jk



Joined: Mon Apr 2nd, 2012
Location: Carthew, Cornwall, United Kingdom
Posts: 6601
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OK so you want to shoot a white object and a grey object on a black background.

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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