The last technical email: metering and putting it all into practise

How did you get on last week shooting on Manual mode? Congratulations if you managed to find Manual mode and worked out how to change the settings independently. 10/10 if you had a go at the homework and got a couple of photos that were broadly what you were aiming for.

If you found it utterly confusing, and are feeling dispirited, you'll be pleased to know that the worst is over. I can't say this too often:

You don't need to shoot on Manual mode all of the time.

You simply need to know:

1. There are 3 settings.

2. They each control the light.

3. They each also have a creative effect (or consequence, for ISO).

Throughout the year, when you have time to concentrate, keep coming back to these first 5 lessons. Try shooting on aperture and shutter priority. Remember to look at the shots you take on auto, and think about whether you could do better if you take control. And at least once a month, have a go on fully auto again.

This week is the last of the technical lessons. Stay with me for one more bumper email, and then you can look forward to the next module which is a creative one: Composition.

METERING

Think back to the first lesson, when you used auto mode and took a photo of something white and another of something black, and they both came out grey.

In the following 3 lessons you learnt how to take control of the 3 settings the camera uses to control the light.

In this lesson you'll learn: "How do I know what the right exposure is?".

You know the camera gets it wrong (it turns everything grey). And you know you can take control. But the final piece of the puzzle is - by exactly how much has the camera got it wrong?

You are not always taking photographs of something that is conveniently all black or all white. Most of the time you are shooting a mix of colours and tones. And it is very difficult to convert a scene into black and white in your head, and then average out all the tones to see how far off the camera is going to be. In the header image for this email for example, the greens and reds of the leaves combine with the sky to create a very difficult image to estimate the correct exposure for. And in fact the camera's auto exposure for that shot underexposed by 3 entire stops.

The good news is that you don't need to constantly convert to black and white in your head and make tone estimates. On the back of every camera there is a display that tells you exactly what the camera is seeing. You can then decide if you and the camera are seeing the same thing, or if the camera is going to get it wrong and expose too dark or too light. The display is called the histogram. It's simply a bar chart of tones, with black tones on the left and white tones on the right, and will look something like this:

Once you know how to interpret the histogram, you can use it to check what the camera is seeing. Then you can either accept that exposure; or override it using any of the priority modes, manual mode, or a great little trick called "exposure compensation" (more on that below).

What is the histogram?

The histogram is just a bar chart showing light values. Imagine a bar chart showing how many apples, pears and oranges a shop sells in a week. If it sells 10 apples, 20 pears and 30 oranges, the bar chart will look like this:

In this image the histogram is showing that there are no black and darker tones at all. Does that look right? It's hard to tell in the reproduction, but that is accurate. In the original image you can still see plenty of detail in the shadows which means they are not completely black.

And at the right hand side, the white bar chart has started to "climb the wall" - it finishes with plenty of white tones showing. This is as sign that the highlights have blown out, and lost all detail - you should be able to see areas of pure white somewhere in the image. Is that correct? Yes - some of the clouds are pure white.

Using the histogram to check exposure

If the histogram in this example had looked like the following diagram, then you would know that the exposure the camera had picked was wrong. Because you can look at the histogram, see that the blacks are touching on the left, and then look at the scene and realise that there are no pure blacks. The histogram is also showing no pure whites - but you know there should be. You would deduce the camera has got the exposure wrong and you can correct it.

A recap:

1. The camera's auto modes and LCD sometimes get the exposure wrong

2. Your eye/brain also sometimes gets things wrong

3. The histogram never gets anything wrong

4. You can see whether the exposure is correct by checking if the histogram looks like it should - you can't rely on your eyes to do this because they often get it wrong

5. If the histogram is not how it should be, you can compensate for the camera's mistake by changing aperture, shutter speed or ISO

Metering

The way that the camera interprets the tones of an image varies depending on which metering mode it is using. To keep this email shorter, I've put Chapter 6 from Workbook 1 as a downloadable pdf over on the AYWMC site. Ch 6 has all the information about histograms and metering, and explains the very very useful trick of using Exposure Compensation to quickly fix exposure errors without shooting fully manual:

RECAP

1. Read this email, and the extra post. Download the pdf.

2. Remember that you don't need to understand histograms at this stage of the course. Like shooting on Manual mode, it's enough that you know that they exist.

3. Work out how to show the histogram on your camera. On most cameras you there is an option to have it showing in the viewfinder before you take the photograph. You can see it changing as you move the camera. On a few cameras you can only see it once you've taken the photograph.

4. Have a go at the homework.

5. Take a deep breath and look forward to the catchup week next week, with an optional fun photo project.