Camera Light meter

blade_922

blade_922

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Name
Omar
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Hey,

Had the DSLR a few weeks now, been taking photos in the hope of improving everytime. Im trying to understand the light meter in the camera, as i keep on reading in alot of threads the importance of it in taking the best picture possible.

So my camera has

-2 -1 0 1 2

I take it thats the light meter?

So have some questions hoping someone has a few minutes to help, even with just short answers. :D

Now what exactly is this telling me when i aim the camera at a particular object? What causes it to change up and down? What can i do to control it? And how by controlling it can i improve the photo im taking? What influence does what the meter says have an influence of the image?

I know i have alot to learn, so understanding the above should help me.

Thank you. :thumbs:
 
Your camera will have several metering modes, evaluative (matrix), centre weighted, spot, or something similar. These determine the area that the meter considers when calcualting light levels. It then tries to get to 18% grey value. Now if using spot for example and point at a black car the meter is going to give a different reading than if you chose a white swan. So you need to think about what is in the viewfinder as well as the metering mode.

Shooting a snow scene for example the meter will underexpose as everything is white and overwhelms the reading and it's trying to get it back to 18% grey. The Mk1 brain is a great instrument and needs to be implemented when using the camera, because it is stupid. The scale is for + and - stop values, so for the snow scene just adjust to overexpose by an extra stop to compensate the meters underexposure. The thing is don't be fooled by dark and light objects, the light on the scene is still the same whether it's white or black, it's just that the meter is seeing it as greater or less light and hence gets the exposure wrong.

Having said all that, you may of course still want to expose for the black say if you really need the detail in that part of the shot at the expense of overexp[osing any light parts of the scene. Hope that helps.
 
artyman said:
Your camera will have several metering modes, evaluative (matrix), centre weighted, spot, or something similar. These determine the area that the meter considers when calcualting light levels. It then tries to get to 18% grey value. Now if using spot for example and point at a black car the meter is going to give a different reading than if you chose a white swan. So you need to think about what is in the viewfinder as well as the metering mode.

Shooting a snow scene for example the meter will underexpose as everything is white and overwhelms the reading and it's trying to get it back to 18% grey. The Mk1 brain is a great instrument and needs to be implemented when using the camera, because it is stupid. The scale is for + and - stop values, so for the snow scene just adjust to overexpose by an extra stop to compensate the meters underexposure. The thing is don't be fooled by dark and light objects, the light on the scene is still the same whether it's white or black, it's just that the meter is seeing it as greater or less light and hence gets the exposure wrong.

Having said all that, you may of course still want to expose for the black say if you really need the detail in that part of the shot at the expense of overexp[osing any light parts of the scene. Hope that helps.
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Hi Ken,

Yes that did help. Thank you. So the camera has several metering modes, as you said these all determine the area that the meter considers when calculating light levels. Now when you say this, are you talking about the area that we see through the viewfinder, ie the object and area around the object? What are the particular purposes we would use the metering modes? Like should one be used over the other for portraits, one over the rest for landscapes? Or does the metering mode depend on the colours and lighting when shooting? Like use one mode for say a landscape photo in the sun during the day, and another mode in low light say just right after sunset?

You said

"It then tries to get to 18% grey value."

Am i right in thinking the camera adjusts what we see say on the liveview lcd screen to get to 18% grey value?

The 18% grey value, is there an explanation to this anywhere to get a better understanding?

Like you said with snow, everything will be underexposed, now to adjust and slightly overexpose to compensate, how do i adjust it? Do you mean by adjusting the aperature/shutterspeed? Or can i adjust the setting of the light meter?

Thank you once again.
 
There is no adjustment of the light meter it just tells you the amount of light that is going to hit the sensor when you open the shutter. It's just a tool to help you get the right exposure. Normally you have to half press the shutter to get a reading.

You need to understand the relationship between ISO, shutter speed and aperture. If you set the camera on full manual you can try the following.

The larger the aperture (smaller number) the more light hits the sensor so opening the aperture further will make the reading go up and closing it will make it go down. I.E. set your aperture to say f/8 and look at the reading, now set it to f/5.6, point it at the same subject and look at the reading, it will have gone up.

The slower the shutter speed the more light will hit the sensor so you can try a similar experiment again. Try raising and lowering the shutter speed to see what it does to the meter reading.

Finally you can look at the ISO as being how sensitive to light the sensor is. The higher the ISO the more sensitive it is so you can get away with shooting in lower light conditions. Setting a higher ISO will cause the reading to go up.

Once you understand all that, as has been mentioned above, you can then look at whether you want to stick with the exposure the camera is recommending or alter to suit the subject.

Now you need to understand why you want to choose certain apertures or shutter speeds.

Have look through the tutorials section for some good information.
 
As above, plus:
Changing the aperture or shutter speed in an auto mode will just give the same exposure: the camera will alter the other to maintain it's target of 18% grey.
 
At the moment I would just use evaluative metering until you get a greater understanding of what you are doing. Reading a good book on the basics of photography exposure is recommended, a visit to your local library should give you plenty to choose from, and read your camera manual so you know how it works, and what buttons do what.
 
Hi,

So the light meter is just to ensure you dont overexpose or underexpose? I understand the relationship between ISO, SS and Aperature no problem and why you would choose certain SS and Aperature.

I also understand what you mean when you talk about the light meter going up and down according to the aperature and SS. Now ideally when taking photos, should you adjust aperature and SS so that you always try to have the light meter sitting at 0? So its not underexposed or overexposed?
 
Blade, may I suggest you have a look at this thread - http://www.talkphotography.co.uk/forums/showthread.php?t=309227 - and pay particular attention to post #41.

Just to provide a brief answer, it is often not the objective to have the meter needle centred. That is a huge misunderstanding that is frequently perpetuated on forums by people who mean well but evidently do not understand what they are talking about. If all you plan to do is to get the meter needled centred then just let autoexposure get you there. It can do it in the blink of an eye, far quicker than you can set an exposure manually, but the odds are that it will not be the best exposure possible.

When the meter needle is at the centre, either whilst metering manually, or when you have exposure compensation set to zero, the camera is telling you that it expects to render the metered part of the scene (once averaged out) as a mid tone equivalent to "middle grey" in brightness.

That's perfect if your scene, or the metered part of it happens to be a mid tone, or averages out to a mid tone. It would be a bit of a disaster if your subject and scene was anything but a mid tone. For a subject/scene that is brighter than a mid tone the meter needle (or EC indicator) should be somewhere towards the positive. For a subject/scene which is dimmer than a mid tone the meter needle (or EC indicator) should be towards the negative side. Quite how far it should be positioned away from 0 depends on the subject/scene and how much brighter or dimmer it is than a standard "middle grey". Knowledge and experience will steer you towards the amounts required.

The metering pattern selected will also influence results. Spot metering allows you to select a very specific part of the subject/scene from which to meter. Partial metering expands the size of that area. Centre weighted average exapnds it almost to the whole frame, but pays more attention to the tones towards the centre of the frame, where the camera assumes your subject to be. Evaluative metering is much more complex. It attempts to determine the type of scene content you have and what sort of exposure would work best. Trying to second guess how the camera thinks whilst in evaluative metering mode is problematic. A lot of people avoid that metering mode altogether because they cannot predict what the camera will make of the scene. If you are trying to learn about metering and setting exposure it is probably the worst metering mode of all to choose. If you are more interested in usable results, rather than learning, then by all means use evaluative metering, but don't expect the results to be optimum. They will usually be a "safe" compromise as best the camera can determine. I only use evaluative metering when I am in a lazy mood and can't be bothered to meter and set exposure accurately. For many people it works well (enough). I tend to avoid it for the most part.
 
I think you have failed to grasp what I said earlier, if you point your camera so a black dog fills the frame, and set up so the meter is at 0 then the camera will make your dog grey as it tries to get to 18% grey. If you want the dog to be black you would need to go towards the minus side to get it looking the correct tonal value.

I suggest you go and shoot some black and white stuff keeping a record of what the camera recommends as an exposure and what you actually give it, then look at the results. Shoot as it recomends and with compensation that way you gain a better understanding.
 
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To simplify things, try this. Meter on either grass or a concrete pathway. Set your camera to these readings, and then take a photo of the scene you wanted to picture. My bet is that your exposure won't be a million miles out....
 
artyman said:
I think you have failed to grasp what I said earlier, if you point your camera so a black dog fills the frame, and set up so the meter is at 0 then the camera will make your dog grey as it tries to get to 18% grey. If you want the dog to be black you would need to go towards the minus side to get it looking the correct tonal value.

I suggest you go and shoot some black and white stuff keeping a record of what the camera recommends as an exposure and what you actually give it, then look at the results. Shoot as it recomends and with compensation that way you gain a better understanding.
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Hi,

Im beginning to understand, obviously just asking what to do wont make me fully understand, so im going to go and shoot some black and white objects as you have said. Understanding from my own experience will hopefully make me understand it more. I will get back to you on my thoughts after trying.

Can i just check, say im going to take a photo of a black object against a beige background. Should i use spot metering so it gets the reading off the black object instead of it as a whole just to understand the black and white difference on the meter?
 
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I would use evaluative, you should still see a difference when you replace the black object for a white one. A couple of props with a constant background is going to provide the best thing to learn from, the neighbours might think you are a bit odd swapping differnt coloured soft toys in the garden, but hey, the whole world is weird, I'm saving up to be eccentric :D
 
Let me just get this right, white will underexpose and black will overexpose right?

I tried it indoors, just got a black salad box and a white tissue. When i pointed the camera and half pressed shutter it dropped to -2, which means it has underexposed right.
When i did the same with the tissue it went to +2 which means it has overexposed. Without changing any of the ISO, Aperature or SS that is.

Now when i was pointing at the tissue, i thought when i stepped the aperature up a bit, higher f number, the tissue looked alot easier on the eye i.e was not overexposed as much and looked much more like in natural light.

With keeping the aperature the same, i then pointed back and half pressed the shutter on the black salad box and it was showing as underexposed, the picture i was seeing on the liveview lcd looked really dull, even though the lighting stayed the same. I had to step down the aperature, smaller f number, to make it look not so underexposed. And just checked that was all on evaluative metering mode.

Am i right in what im saying above?

Now that i have got my head round this, if im right in thinking what i did and why, are there any other test experiments anyone can personally recommend.

I hope you dont mind, but i have a weird method of learning, i like to think ahead before i carry out an experiment/test to think why something will happen and for what reason even though what im thinking may be wrong. It helps me understand that when i do carry out the test, i understand why i thought what i did before hand and why its wrong, and what im doing is right. Weird huh? But it works wonders, we should all try this :D

The whole world is weird and different Ken, thats what makes it a wonderful place :D You dont have to save up to be eccentric, all you have to do is what pleases you and forget the rest. If you live life worrying about what other people think of you, then i think those type of people live a lie.
 
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blade_922 said:
Let me just get this right, white will underexpose and black will overexpose right?

I tried it indoors, just got a black salad box and a white tissue. When i pointed the camera and half pressed shutter it dropped to -2, which means it has underexposed right.
When i did the same with the tissue it went to +2 which means it has overexposed. Without changing any of the ISO, Aperature or SS that is.

Now when i was pointing at the tissue, i thought when i stepped the aperature up a bit, higher f number, the tissue looked alot easier on the eye i.e was not overexposed as much and looked much more like in natural light.

With keeping the aperature the same, i then pointed back and half pressed the shutter on the black salad box and it was showing as underexposed, the picture i was seeing on the liveview lcd looked really dull, even though the lighting stayed the same. I had to step down the aperature, smaller f number, to make it look not so underexposed. And just checked that was all on evaluative metering mode.

Am i right in what im saying above?

Now that i have got my head round this, if im right in thinking what i did and why, are there any other test experiments anyone can personally recommend.

I hope you dont mind, but i have a weird method of learning, i like to think ahead before i carry out an experiment/test to think why something will happen and for what reason even though what im thinking may be wrong. It helps me understand that when i do carry out the test, i understand why i thought what i did before hand and why its wrong, and what im doing is right. Weird huh? But it works wonders, we should all try this :D

The whole world is weird and different Ken, thats what makes it a wonderful place :D You dont have to save up to be eccentric, all you have to do is what pleases you and forget the rest. If you live life worrying about what other people think of you, then i think those type of people live a lie.
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Yeah I would recommend you get out and take some bloody pictures.
;)

Don't try to understand everything too quickly, forget about metering modes for a minute and stick the camera on evaluative, aperture priority and ride the exposure compensation dial to get your pics how you want them. Look at your pics on the computer and note how adjusting the comp. Changes things. BTW EC will change the shutter speed in aperture priority, you select the aperture, camera selects shutter speed for what its metered with that aperture and EC adjusts that shutter speed.

When you understand what's going on you can try the other metering modes and full manual control. Aperture priority isn't less of a professional way to use the camera, its just another way.
 
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