JimBart wrote:
Need a little help… seems like I’ve forgotten something Tell me if I’m correct and if not please set me straight
Attempting to get the detail of the subject against the background
1. Light (white, creme etc) subject against a dark background equal a negative ex comp
2. Light subject against light background equal a zero or plus exp comp
3. Dark subject against dark background equals plus exp comp
4. Dark subject against lighter or bright background equals a zero or minus exp comp
5. Subject in front of a bright or dark no curtained window equals a negative exp comp.
Thanks for setting me straight
Need a little help… seems like I’ve forgotten some... (
show quote)
Your light meter assumes all subjects are of an average brightness. It doesn’t know that they are black or white, light or dark.
An 18% reflectance target (gray card) is used as a standard reference.
With all the scenes you mention the exposure would be the same if your lighting was identical. Changing subject and background color has a small effect, though.
Many people use an incident light meter to measure the light falling on their scene. When they use that, darker objects record darker ( as they should), and lighter object record lighter ( as they should). If you are using a camera’s built in meter, rather than an incident light meter, you can get your exposure by metering a gray card placed near the subject.
Failing that: you have to figure your corrections in your head.
1) light against dark background. If most of the area is dark then the camera will want to slow the shutter or open the aperture to let in more light. It assumes that black mass is a gray mass with little light falling on it. That leads to over exposure, so your light subject would loos highlight details.
The correction would be typically under exposing (based on the camera’s suggested exposure) by 2 to 3 f/stops.
Number 4, dark against light back ground is exactly the opposite. Over expose 2 to 3 stops more than the meter suggests.
The reason: the light background is interpreted by the camera as an overly lit gray area. It wants to record that as a gray. But if your highlights are grey ( not white) then your shadows will be so underexposed that there will be no details captured. With film you are stuck. With digital you can boost the image somewhat in post processing, but you’ll see increased degradation in the shadow areas.
2 and 3 light against light and the opposite, dark against dark. Again opposites. The meter thinks they are overlit gray subjects, or underlit gray subjects, and opens or closes the aperture accordingly.
To avoid underexposing light subjects, open the lens 2 to 3 stops. Give the film or digital sensor more light to play with. With dark scenes the camera is already getting too much light coming in—enough to make black look gray. Close the lens 2-3 stops to keep put the excess.
5 if your subject is a person, just move in close enough to meter off their face and lock in that exposure. It isn’t perfect. Some faces are brighter or darker than a gray card—and you can compensate based on your observation—adding more light if the face is brighter and restricting some light if the face is darker than a gray card. Usually faces are within 1 stop of ‘average’ though, which is well within the acceptable exposure range, so just metering the face should be close enough to tweek in post processing.
There is however a second problem in question 5 which is implied: how much light is falling on the front of the subject? If all the light ( from a bright window) is behind the subject then will there be any on the other side, or is this just going to be a silhouette? Without a fill-in flash, or some well placed reflectors, you could get a technically acceptable exposure but still have an awful picture. You usually need some kind of directional light to cast some shadows that our brains can interpret as depth.