Camera Light Metre

This is a had topic to grasp but understanding how your light meter works is fundamental to getting exposures.

It’s important to know that your camera’s light metre is calibrated to whats known as middle grey. In short your camera wants to turn everything you point it at, to a middle grey.

Now for a lot of scenes this is generally ok, but as you get better and more familiar with your camera, you will also want to make artistic decisions for your self. So instead of the camera telling you what you want, you have to know what adjustments are necessary to achieve your vision of what the image should be.

If you point your camera at a white wall you would reasonably expect to get a white image on your LCD. But thats not the case. Your camera wants to take that white wall and make it middle grey. so to realise your vision you need to make adjustments that tell the camera to make the image white.


The target above is a calibrated to middle grey and very useful as a reference.

If we look at a chart showing tones going from black to white, we can see that white with detail is +2 stops from middle grey. Conversely if we look at -2 stops we have black but wuth some detail.

We can use this information to help us get the correct exposure for a given scene.

Say we are going to take a photo of a white swan, then its important that we retain detail on the bird. We know the bird is not pure white, so we can asume +2 stops will give us white with detail. With me so far?

Next we zoom in and fill the view finder with the bird and dial in the correct exposure +2 stops.

spot metre ref.png

Now take a test shot. If the image is to light adjust, to dark adjust.

Next up The Histogram, your best friend…

The exposure triangle

Getting the correct exposure is crucial to getting good images.  So the question must be how to get the best exposure. Well some help is at hand.  You camera has a built in meter, it also has a Histogram which is a representation of the tones in your image and can be the source of great feedback.  Then lastly and perhaps less reliable is the LCD on the back of your camera. (use with caution)

So where to start.  Well you have to know from the get go, that everything in photography is a compromise.  The start ing point is what do you want to achieve and what is your priority.

Assuming we are in good light for this example, ie day light. the first question to answer is what is priority, is it everything in focus, is it freeze the action. is it picture quality?

Lets say its freeze the action, I want the subject tack sharp, so what shutter speed do I need to achieve that.  Lets say 1/1000. so dial that in.  ok so whats the next priority, is it quality or depth of field?  Lets say its quality so set the ISO as low as possible.  The remaining variable would be to set the aperture.

Setting the aperture is a matter of adjusting the aperture control until the light meter in the camera is at the centre as below.

Now take a test shot as decide if you think the image is just right, dark or light.

If necessary adjust the aperture to either let in more or less light.

Thats your camera locked in and as long as the light doesn’t change, you can then concentrate on taking good photos.



ISO adjusts the sensitivity of your camera to light.  As in all photography there are compromises.  As you increase the ISO to make your camera more sensitive, there is a slight loss in quality (noise).  The higher you go the more you loose.

But modern cameras can work at high ISO values not imaginable only a few years ago.  Modern cameras can create very clean images at even 1600 ISO and higher.

I would rather have a image that has slight noise but is sharp, rather than an image that had camera shake, just because I didn’t want to put the ISO up and loose some quality.

Noise in an image can usually be dealt with in Postproduction, a unsharp image is much more difficult to save.

Next up Aperature….

So you got a camera What next.

Your new camera no matter how fancy captures data. Its our job to capture as much data as possible.

You camera is a machine and will get you to a great starting place. But you are the artist and you need to make the creative decisions.

The best way to capture the maximum data is to get the exposure correct.

ISO Aperture and shutter speed are the three controls that make up your exposure. This is comonly known as the exposure triangle

We will look at these one at a time, but before we do, we will be using the word “stop’s” a lot so let me explain.

Each of the above controls mentioned are divided by one stop. A stop of light is either 1/2 as much light or twice as much light. From f8 to f16 lets in 1/2 as much light. Or 1/60 to 1/30 lets in twice the amount of light.

Stops can be further divided by 3 clicks known as 1/3 of a stop.

So in the next post we will look at the first of these controls. ISO