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04-22-2008, 07:55 AM   #1
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Complete idiot's guide to metering

Hello ,i'm new on the forum here,this is my first post
i would like to learn what metering is for ...can someone help me?

04-22-2008, 08:47 AM   #2
Ash
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Welcome Vlad,
Metering is the term used when the camera's built in light sensor calculates the amount of light needed to fall on the sensor to get an adequately exposed photo. Is the jargon too much? If so, I'll simply say it's how the camera knows how much light it needs to make an image.

It depends on what mode your camera is in as to how the camera will adjust its settings to keep the amount of light falling on the sensor adequate. In auto modes, the camera selects everything. In Av mode you select the aperture, the camera calculates the shutter speed. In Tv, vice versa. It also matters what the sensitivity (ISO value) is, so do read up on this important triad of settings in a book like "Understanding exposure" by Bryan Peterson.

Others on this forum are much more knowledgable than I am, so don't be afraid to ask all the questions you think are silly but many others would be afraid to ask...

Last edited by Ash; 04-22-2008 at 03:45 PM.
04-22-2008, 10:23 AM   #3
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hmmm,so i see,besides the settings of iso,aperture and shutter speed there is this metering thing too...hmm...
04-22-2008, 11:29 AM   #4
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QuoteOriginally posted by Vlad Quote
hmmm,so i see,besides the settings of iso,aperture and shutter speed there is this metering thing too...hmm...
metering is the act of measuring the light the camera sees. The camera has several metering modes ... matrix, center weighted and spot. These select what part of the "image" to evaluate.

What happens after metering is setting the exposure. This is the process of selecting the ISO, Aperture, and shutter speed. The camera has many modes for this. from Bulb, to manual, to Av, Tv, P, Auto, Scene, Hyper-this Hyper-that....

All these really do is select an ISO, aperture and shutter speed. You pick the mode depending on how much input you want to have in this process. In manual, you pick all three. In the Scene modes, you pick nothing (maybe ISO).

When metering, the camera can only guess at what the scene is. I knows how much of the scene is dark, how much is light etc... but it doesnt know if the white part is the brides dress and the dark part is not important, or if the white part is snow, and the dark part is your son's face.

So, the camera has to guess. If you dont like the guess, you can switch from program mode to manual mode and change the settings, or you can stay in program mode and add or subtract "EV compensation". But if you dont like the guess the camera makes, you should tell it what you want it to do.

04-22-2008, 12:02 PM   #5
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A suggestion I was given early in my days of photography (not too long ago!!) was to read Bryan Peterson's book "Understanding Exposure". It does a very good job of explaining aperture, shutter speed, sensitivity (ISO), and lighting. I first got a copy from my local library, liked it so well, I purchased a copy from Amazon.

In the future, I would suggest posting questions like this under either "General Pentax Photography" or "Pentax DSLR Discussion" - you will get move visibility to your questions.
04-22-2008, 12:50 PM   #6
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i see...well i think i will look for the book you gave me...
by the way... i am 20 years old...do you think it's a good age to start being a photographer?
04-22-2008, 01:51 PM   #7
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Sure! Any time from about 13 to 100 would be a good age! I started to get a bit more serious at forty something, which means I will catch on slower than you, but can still eventually get there!
04-23-2008, 07:28 AM   #8
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Just so you really understand metering, as others have mentioned, it is the way the camera calculates the exposure.

The term comes from the fact that origonally, cameras did not do any of this, it was the photographer, who used a hand held light meter, hence the term metering.

A light meter is essentually a meter with a moving needle (or today perhpaps a digital readout) that would measure the absolute amount of light.

It had in addition, a set of circular sliding dials (like a circular slide rule), with markings of F-stops film speeds and shutter speeds. This was used to calculate, with a given film speed, the combination of shutter and apature (f stop) you wanted.

All of this is now done inside the camera automatically but is still called metering.

Some have mentioned different modes, spot, center weighted and matrix metering, all these really mean is whether the camera meters from a very tiny sensor in the middle of the frame (spot), whether it averages the exposure over a broad area, with a sligt preference to the center of the frame (center weighted) or whether using somewhere up to 11 sensors the camera applies a host of calculations (and guesses) how to interpret the scene based upon the internal computer's program.

04-24-2008, 07:32 AM   #9
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QuoteOriginally posted by Vlad Quote
hmmm,so i see,besides the settings of iso,aperture and shutter speed there is this metering thing too...hmm...
Vlad, here's my explanation. Forgive my silly analogies

Exposure= how much light used to create the image. This is controlled by a few variables when the shutter button is pressed which are the following three items Aperture, Shutter Speed, and ISO:

Aperture=size of the variable controlled opening in the lense (think of this as how far open your eyeball is. All the way, half open, etc)

Shutter Speed=time that the shutter in the camera is actually open (think of this as how long your eye is open)

ISO Sensitivity=the sensitivity of the sensor (think of this as how sensitive your eyes are to light)

The camera can automaticall or manually manipulate all three of these variables which effect the overall exposure or brightness / darkness of the image. However....all three of these could be adjusted in multiple ways to get the proper exposure. IE, your eye is wide open, but only for a second...or it's only half open, but for a number of seconds. What you will learn, that changing each one of these has a different effect on the image. For example, using a wide aperture (eye more open) will cause things in the near foreground and far background to be less in focus. Having a long shutter speed (eye open longer) will allow you to catch the movement of objects, which can be desirable or not, depending on the situation. All these variables and effects of each of them is why cameras have automatic and scene modes to freeze action in "sports mode" or focus everything in "landscape mode", etc.

That's exposure and the three controls that set exposure.

Metering is the camera using it's light sensing technology to try to measure the necessary lighting and therefore control or recommend the right exposure. Think of using a computerized light meter so that you could figure out what you will need to do with your eyes (wide open, how long, etc) to be able to see things properly. There are different metering modes, so that you can control at what position in the frame (or picture) the cameras metering sensor will be aimed at. Then you can also do things like lock the metering sensor after you point it at something so that it doesn't automatically change when you point it at something else.

Lots of reading is the best way to understand all of this! Good luck and most of all be patient and have fun!!

Last edited by tbone-ike; 04-24-2008 at 01:25 PM.
04-24-2008, 02:35 PM   #10
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Vlad,

I was in your shoes not too long ago .. these forums are amazingly helpful, and the Pentax community is unlike any other I've seen out there. Ask questions, no matter what - you will learn lots.

With that being said, here are some helpful links I have stumbled across in my journey to understanding all this stuff!

Back to Basics | DIYPhotography.net (there are several links at bottom of this page for Exposure articles)
Digital Photography Composition Tips

And, this last link is for a free, no-obligation online course. It's a trial course, I liked it so much that I signed up for a year of courses!! However, you can just do the free trial and you will learn LOTS about DSLR Photography.

Digital SLR Photography: A FREE Course Preview - See How Our Online Photography Classes Work: Overview

Happy learning!
04-25-2008, 04:16 PM   #11
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is there a consensus on metering time?

3, 10, or 30 seconds.

what is yours set at?
04-25-2008, 04:32 PM   #12
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Metering time doesnt affect the metering per se. It is a usability feature. This is how long the metering function remains active before going into a power save mode.

I've changed mine only a couple of times, I think its on 10 seconds now. I assume the shorter the time, the longer the battery life... but I coudlnt say by how much. And no amount is long enough that I am not tapping the shutter release to "wake up" the camera. I now do this almost absentmindedly. It is most apparent to me (and annoying) when using manual lenses in manual mode. I push the AEL button, push the AEL button... nothing... then I remember to tap the shutter to wake up the camera... then the AEL stops down and sets the exposure.

I wish either would do it. (K100D)
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