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How do you know what to meter befor taking a photo?

  • How do you know what to meter be for taking a photo, im reading a book and he is panning a car in a field of yellow flowers and he said he metered the blue sky in the photo there is no blue sky so why did he meter the sky (if this make sense) another one is i took a photo of the outside of a church the sky was dull grey and someone said should of metered the grass. How do you know what to meter ?

  • Answer:

    To answer your question we need to know what the metering system in all cameras is actually doing. The first thing is the meter sees the world in B&W, it sees a series of grey tones from white to black. What the meter does then is to read the scene in front of it and finds the average, it then sets the camera so that average is exposed for 18% grey. In other words that average will be mid grey. Cameras usually have 3 modes for taking the average reading, zonal, centre weighted and spot. The zonal reads all scene by independently reading the all the zones and works out 18% grey for the overall image from that. Centre weighted biases the exposure to the centre of the scene, and spot metering reads a small spot usually in the centre of the scene, but you can also tell your camera to take a spot reading at the same place in the scene that the Auto Focus is using. The subject you meter on is the thing you want to be correctly(ish) exposed. If there is a person in the picture you can spot meter on their face so that will be exposed as the mid grey (18% grey), the rest of the scene takes pot luck. If you meter the sky the for-ground will be under-exposed even to silhouette, which may be what you want to do. The problem with this 'reflected light' exposure is it makes no allowance for the tone of the subject, so if your scene is predominately white (a snow scene for instance) then it will set the camera to make that 18% grey, you'll get grey snow, it will under expose usually by around 1 f stop. This is why your camera will have exposure compensation so you can, in this case, force the camera to expose the shot 1 stop more than the metering system is telling it to. The opposite is also true, if the scene is predominantly dark tones, a black cat on coal for instance, it will set the camera to make the subject a mid grey, it will over-expose. This is why I used the term correct(ish) as reflected light meter reading can be (and often are) incorrect. You can get around this by point your camera at something that is mid grey (18% grey) and you can buy grey cards for doing just this. You would use spot metering and take the exposure off the grey card, then your overall exposure will be more correct. The reason why the person said to meter off the grass is that grass is often (but not always) a mid grey to the metering system. There are separate 'incident' meters that meters the light falling onto your subject you can buy, with these you set the shutter speed and ISO your camera is using, go to the subject, point the meter back at the camera, press the 'take a reading' button and it will tell you the correct f number to use accurate to 1/10th of a stop. These are always spot on. Flash meters can do this too as well as trigger any flash you might be using and give you the correct f number incorporating the light from the flash as well as the ambient light. Chris

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When we look at a scene we see it differently than our camera does. The light meter in our camera uses 18% gray as its basis for setting exposure. 18% gray is the reflectance of an average scene such as a horse in a green pasture under a blue sky on a sunny day. Under these conditions the camera's meter does a good job of giving us a good exposure. When conditions are less than ideal the camera's meter can often be fooled. Suppose we have a subject in bright light standing against a dark background. If we depend on the meter, our subject will be overexposed since the meter sets exposure based on 18% gray. In this situation we'd have to take corrective action. 1) Zoom in on the subject, meter, lock that exposure, zoom out, compose and shoot. 2) Walk closer to the subject, meter, lock that exposure, walk back, compose and shoot. 3) If the camera has a spot meter setting switch to it and meter the subject. 4) Use -1 or -2 EV (Exposure Compensation), compose and shoot. Now suppose we had the opposite situation - a subject against a bright background. Here again depending on the camera's meter will not give us the desired results unless we want the subject to be a silhouette - very underexposed. If we want detail in the subject we can try 1, 2 and 3 above but our 4th. option will be to use +1 or +2 EV. I've no idea what book you've been reading but I suggest Bryan Peterson's book "Understanding Exposure". These sites will also help you: http://www.digital-photography-school.com http://www.photonhead.com http://www.kamerasimulator.se/eng/?page_id=2 http://www.illustratedphotography.com/photography-tips/basic

EDWIN

When you have time to, you cannot beat Ansel Adams Zone Method which account for all sections of a scene. Of course this is done in an entirely manual situation, and is most suited for black and white film but it's nonetheless applicable for other situations. Obviously this isn't really practical in all situations, even in landscape photography it is often too slow in a dynamic situation. So you can reduce the number of readings you take. Take one of the highlights and one of the shadows that will provide you with a ballpark within which you can work. Think what details you want to capture, and what detail you have to/can sacrifice. Lets use one of my photos for example, http://www.flickr.com/photos/ciao_chao/5340464975/ this is a good one because there is a lot of variation in light. The annotations on this image explain a what I've written below. I wanted to capture detail in the right, but if I exposed that as my main subject I'd lose the rest of the scene. So I brought that to -1.7 EV on the meter, even then the sky was showing a reading of above +2 EV, but I accepted that I was inevitably going to get small areas of blown highlights, but if I shot in RAW most of it would still be there. Now lets look at a cloudy situation, here I wanted to make the most of the texture in the cloud (I'll admit it's enhanced a little). So I had to make sure that there was plenty of detail in the highlights, and I don't get nasty bits of white in the middle of the cloud. So I had to choose to underexpose the mountain in the background, though that has turned out to compliment the image quite well. http://www.flickr.com/photos/ciao_chao/4917619893/

CiaoChao

You don't ever "know" what to meter - it will depend on the lighting conditions. If the sky is bright, and you don't want to burn it out - meter the sky (but anything in the shadows will be under exposed). If you want the subject fully exposed, meter the subject - but then the highlights might get blown. If you want both subject and background half decent, meter something in the mid range in the scene (ideally an 18% grey card) or just compensate by tweaking the exposure by one stop. There is no right and wrong in this - you need to use your creativity and skill. If you are having problems with exposure try shooting in RAW then fix in post processing, or use exposure bracketing. If you want more accuracy get an exposure meter.

B K

Blue sky and green grass are mid-tones - the author was metering on these to tell the light meter what a mid-tone looks like under these lighting conditions. As long as the exposure is then 'locked' using the AEL button OR the setting he got were dialled in on manual exposure, the actual things he metered on do not have to be in the scene. You meter what's important in the scene (by spot metering) and then deciding where on a tonal scale (mid-tone, highlight with detail or shadow with detail) you wish to place that subject.

deep blue2

For metering exposure: I assume you are a dSLR user? Shoot raw not jpeg for starters, it is vitally important for post-processing. Does your body have an AEL button? If so, learn how to use it! Meter the highlights, such as the sky, not the darker areas. Using raw in post-processing, you can lighten the darker areas using fill for example and keep the detail, but you can not undo a white blown-out sky that should have been blue, the detail has already been lost. :D See what I mean?

Jack F

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