Light Metering

[FotoPhreak]

"If there is a lit object that you care about in the scene, take your meter reading from that." - quote from www.betterphoto.com

Quick question relating to the above quote:

* Is the quote referring to a light reading being taken by a light meter, or is it possible to do this through the 300D itself??

* Can someone please explain how metering actually works.

More specifically ... in different posts I have read peoples comments (particularly for music concerts) saying that to get the best exposure meter off the musician ... or in the above quotes case (which is referring to a fireworks shot) meter off a different subject (i.e. building) and then recompose to include the fireworks -> what essentially is this doing?!?!

[robertwgross]

What is metering? Wow! (That was about an hour or more of photography class).

If you were trying to take a picture of a black cat eating licorice in a coal bin at midnight, can you accept it that the camera would have to be set for either a wide open aperture, or a very slow shutter time, or both?

If you were trying to take a picture directly at the sun (not recommended) at high noon, can you accept it that the camera would have to be set for either a closed down aperture, or a very fast shutter time, or both?

I will conveniently ignore ISO sensitivity for the moment and assume it to be constant.

Inside virtually every modern camera, there is a light meter. Possibly, it could measure light and give you a light gauge number of some sort, but then the human user would have to translate that into some sort of aperture and shutter settings that will produce a good result. Most human users find that translation to be messy, at best.

So, the meter inside is coupled to a very simple computer. In some cases, the user sets the lens aperture, and then the meter/computer will choose the correct shutter time to make the metered target appear normally exposed. In other cases, the user sets the shutter time and the meter/computer will choose the correct lens aperture to do the same thing. In more complicated situations, the silly user will leave the camera in Green Box mode, and that forces the meter/computer to make all of the decisions by average guesswork.

If your overall subject has pieces of black, gray, and white, you could aim the light meter at the black piece and get one solution for aperture and shutter. Then you could move it slightly to point more at the gray piece, and you would get a completely different solution. Then you could move it slightly to point more at the white piece, and you would get something different yet.

Which solution (aperture, shutter, etc.) would be correct? [Hard to answer]. So, if the metering pattern in your camera is set widely, it will average all three pieces together and come up with an answer that is good, on the average, but it might be wrong for what the user really intended. If the metering pattern is more of a point, then it will not average much, and it will read only that one point. If that one point happens to be unusually bright or dark, then the user just shot himself in the foot for average subjects.

That is where the mastery of photographic exposure is valuable. A really experienced photographer can almost "eyeball meter" the subject. He can pick out what parts of the subject are bright or dark, and he can avoid letting his camera's meter/computer be too far fooled. That gets into Exposure Compensation.

Your assignment is to learn the different meter patterns that your camera has, and then practice using them until you choose one or the other instinctively.

---Bob Gross---

[scottbergerphoto]

I suggest you read and memorize this article from Kodak:
http://www.kodak.com/global/en/consumer/products/techInfo/af9/
Scott

[PacAce]

If you were trying to take a picture of a black cat eating licorice in a coal bin at midnight, can you accept it that the camera would have to be set for either a wide open aperture, or a very slow shutter time, or both?


And what make it even more confusing is that you have to just ignore the meter recommendation and close the aperture down or increase the shutter speed by about 1 or 1.5 stops to get the exposure about right. :?

That is, of course, if you don't want a gray cat eating gray licorice in a gray coal bin. :mrgreen:

[robertwgross]

And what make it even more confusing is that you have to just ignore the meter recommendation and close the aperture down or increase the shutter speed by about 1 or 1.5 stops to get the exposure about right.


However, that gets us into Exposure Compensation. I always like to wait until the second class session to spring that on 'em.

---Bob Gross---

[DaveG]

"If there is a lit object that you care about in the scene, take your meter reading from that." - quote from www.betterphoto.com

Quick question relating to the above quote:

* Is the quote referring to a light reading being taken by a light meter, or is it possible to do this through the 300D itself??

* Can someone please explain how metering actually works.

More specifically ... in different posts I have read peoples comments (particularly for music concerts) saying that to get the best exposure meter off the musician ... or in the above quotes case (which is referring to a fireworks shot) meter off a different subject (i.e. building) and then recompose to include the fireworks -> what essentially is this doing?!?!

The meter in your camera thinks that the world is 18% grey. Take a meter reading of a black door and change the aperture and shutterspeed until the needle in your camera is centered. Then do a meter reading of a white door and make the same aperture/shutterspeed changes until once again the needle is centered. If you use those two indicated exposures, instead of ending up with a white door and a black door, you will end up with two 18% grey doors. That's because the meter sees the white door and thinks "This is an 18% grey door with LOTS of light on it." or the meter sees the black door and thinks, "This is an 18% grey door with very little light on it."

That in a nutshell is what the meter thinks and how very easily fooled it can be. The "... a lit object that you care about ..." statement means that you go up close to the "lit object" and do the reading off of that since I'm infering that the rest of the seen isn't lit and will fool your meter. Most scenes are around 18% grey and are "average"; and that's why the in-meter works well most of the time. But you will have to be careful if you shoot with a lot of snow on the ground because the meter will want to give you an exposure that will turn the white snow into 18% grey.

Oh a point, light meters USED to think that the world was 18% grey. The manufacturers may have changed that to another percentage. Rest assured that EVERYONE changed and that if the 18% grey is now 14% (or whatever) the same principles hold true.

Fireworks are one of those "unmeterable" subjects. I go to the Kodak Professional Photoguide and look it up on the "Existing Light Dial". You will find your subject on a table on top of the page. "Aerial display of fireworks" indicates a letter F. You set the ISO of your film or capture next to the letter F on the dial and get an aperture reading. In this case an ISO of 100 suggests an aperture to use of f8 and a shutterspeed of at least four seconds to capture multiple fireworks bursts. I usually use eight seconds at the same f8. There are other "pretty much impossible to meter" situations on this dial and you might want to have a look at a copy of this invaluable publication.

[scottbergerphoto]

Another Kodak Publication available for retail sale, not on the Kodak website is "Existing Light Photography", part of the Kodak Workshop series. It has a number of tables for unmeasureable lighting situations.
http://www.amazon.com/exec/obidos/tg/detail/-/0879857447/qid=1076961970//ref=sr_8_xs_ap_i1_xgl14/103-9770805-4111009?v=glance&s=books&n=507846
Scott

[robertwgross]

Here is food for thought:

Some meters have the ability to measure color. Why couldn't they use that to do automatic exposure compensation to the normal metering?

In other words, if the normal metering suggested X aperture and Y shutter, why couldn't the color be read and used to tweak the normal settings, just the way that an experienced photographer will twist the exposure compensation dial?

Or, are we trying to gild the lily here?

---Bob Gross---

[scottbergerphoto]

Here is food for thought:

Some meters have the ability to measure color. Why couldn't they use that to do automatic exposure compensation to the normal metering?

In other words, if the normal metering suggested X aperture and Y shutter, why couldn't the color be read and used to tweak the normal settings, just the way that an experienced photographer will twist the exposure compensation dial?

Or, are we trying to gild the lily here?

---Bob Gross---
As a matter of fact, the Nikon F5's meter does take into account color in it's matrix metering mode. Since I bought the 10D, it mostly sits on my shelf.
Scott

[PacAce]

And what make it even more confusing is that you have to just ignore the meter recommendation and close the aperture down or increase the shutter speed by about 1 or 1.5 stops to get the exposure about right.


However, that gets us into Exposure Compensation. I always like to wait until the second class session to spring that on 'em.

---Bob Gross---

Bob, you sly fox you! :mrgreen:

[robertwgross]

Bob, you sly fox you!

No fox here. Although I have been accused of looking like a marmot.

---Bob Gross---

[DaveG]

Here is food for thought:

Some meters have the ability to measure color. Why couldn't they use that to do automatic exposure compensation to the normal metering?

In other words, if the normal metering suggested X aperture and Y shutter, why couldn't the color be read and used to tweak the normal settings, just the way that an experienced photographer will twist the exposure compensation dial?

Or, are we trying to gild the lily here?

---Bob Gross---

Those colour meters will just tell you what the colour temperture is. Useful in the old days when you were trying to figure out filtration to take a colour cast out of a room. But they never gave you an exposure read out but information in colour temperture measured (I seem to remember) in mireds, or mired shift.

I know that black and white films have a different ISO depending on whether the exposure is with daylight or incandescent light, but almost no one pays (or paid) any attention. In any case I don't see how the colour temperture would make an exposure any more precise than just using the histogram.

[PacAce]

Bob, you sly fox you!

No fox here. Although I have been accused of looking like a marmot.

---Bob Gross---

Marmot????

<looking up the word in the dictionary...>

Ok, got it... :lol:

That's what's so great about this forum...you learn something new all the time. :mrgreen:

[robertwgross]

Marmot????


From time to time, I have been accused of being a nature photographer. If you get up high into the mountains, the furry little creature running around in the rocks is a marmot. That is closely related to the groundhog, so think: mammal, furry, bigger than a squirrel, smaller than a dog.

They are quite photogenic with different shades of brown fur and a noble pose.

---Bob Gross---

[Onwuma]

"If there is a lit object that you care about in the scene, take your meter reading from that." - quote from www.betterphoto.com (http://www.betterphoto.com)

Quick question relating to the above quote:

* Is the quote referring to a light reading being taken by a light meter, or is it possible to do this through the 300D itself??

* Can someone please explain how metering actually works.

More specifically ... in different posts I have read peoples comments (particularly for music concerts) saying that to get the best exposure meter off the musician ... or in the above quotes case (which is referring to a fireworks shot) meter off a different subject (i.e. building) and then recompose to include the fireworks -> what essentially is this doing?!?!
I recommend you pick up and read "The Photographic guide to exposure" by Chris Weston. The simple answer to your question is that Digital SLRs like the 300D contains a meter inside. Just set the camera to manual mode and adjust your aperture and shutter rate until the light meter says the scene is properly exposed.

The problem with in camera light meters is that they average the entire scene to middle gray. So a picture of white snow will not be exposed long enough to look white, instead it will appear middle gray. The same applies with a dark object, like a black bear. The camera will think that black is supposed to appear middle gray and the reading it gives could actually over expose the shot.