lightmeter question

[grooski]

I've had this question about the light meter. (Example) Lets say you go to the lake and you take an exposure at medium tone.than you go home then come back at the sunset and take an exposure also at medium tone. Does this mean that there is the same amount of light, or what? How does the light meter knows that this is medium tone with the givin f-stop and shutter? It would be great if you could answer this. Thanks!

 

[ksmattfish]

I'm not sure I understand your question exactly, but here goes...

The light meter tells you what the proper exposure settings are to get middle gray in any given lighting situation. If you meter a white rock, it tells you how to get middle gray. If you meter a black rock, it tells you how to get middle gray.

If you measure the light of a scene at two different times of day, and the readings are the same, then yes, there is the same amount of light. The camera settings would be the same both times.

If one time there is less light than the other, but you exposed the same scene for middle gray both times, then the camera settings would be different, but the negative density should be pretty much the same for both shots (assuming identical developing).

 

[ksmattfish]

Grooski wrote: "How does you light meter know that this (any situation) would be medium ton, over exposed or under exposed"

I assume that this post is part of this thread. Use the "reply" rather than "new topic".

Ah ha!!! :sun: That is the key, your light meter does not know.

The lightmeter can only measure the light falling on it's sensor or reflecting from the subject, and give you an exposure recommendation that will produce middle gray tones. This only works if your scene is either all middle gray, or made up half and half with black and white tones.

For any subject/scene that is primarily darker than middle gray, your light meter will give a recommendation that will over-expose; middle gray is lighter than black.

For any subject/scene that is primarily lighter than middle gray, your light meter will give a recommendation that will under-expose; middle gray is darker than white.

 

[grooski]

I know that the lightmeter doesn't "know". But it just simle just measures the amount of light. But did someone come up with it so this much light and your settings would be medium tone under or over exposed and they just kinove put it in the light meter?

 

[Big Mike]

Someone, somewhere decided that 18% (middle gray) was the best setting for camera meters.

 

[ksmattfish]

Someone, somewhere decided that 18% (middle gray) was the best setting for camera meters.

It's the middle of the scale. The idea is that average out the tones in scenes likely to be photographed, and it would be middle gray. Is this realistic? No, but it works much of the time. A neg that is exposed for middle gray tones will probably always be printable, even if the scene is mostly dark or light; at most you'd probably end up with a 2 stop over or underexposure. While if your meter measured for the ends of the range, there would be a higher chance that the recommended exposure would be wrong. If my meter measures for the dark end of the scale, and I'm metering a light scene, then the meter will tell me how to turn the light subject very dark, which would be a significant underexposure (like 5+ stops).