Understanding your camera's metering

10th August 2015
There's been a few good posts on local Facebook photography pages about learning the 3 main aspects of photography in respect of exposure.

The 3 things that always have to be balanced out are...

1) Shutter Speed, a fast one such as 1/500 to freeze sport action, or several seconds for that smooth water effect in a long exposure.
2) Aperture (F-Stop), a large aperture (confusingly a small number) such as F2.8 will only have your target in focus, everything else will be blurry - good for portraits... or F22 to get almost everything sharp - within reason.
3) ISO (in the old days film speed). ISO 100 is ideal if you can get away with it, but as the ambient light drops, you have to increase your ISO to something like 1600.

But that's all covered in many good web pages, and I wanted to touch on something else.
If you can get a basic grasp of the 3 things above ^^^ and then also learn this next "lesson" then you'll have a good understanding of what your camera is trying to produce.

We've all taken photos of wonderful sunsets with a golden ball of fire for the sun and fantastic red clouds - but if we are to be honest a lot of the times we take those, it was nothing like what you were seeing with your own eye.

Every camera in any of the fully or semi-automatic modes (Full Auto , Programme, AV, TV etc) will try to give you a photograph of what it thinks it is looking at. Camera sensors are many years away from being as good as the human eye for being able to see dark shadow areas, and bright skies at the same time.
What a every camera does is gives you an estimated photo of the scene it has been shown.
In essence it will look at everything in the frame and average all the brightness levels out to a mid grey.

If you were to take a photo of a full black card your camera will think "ooo that's a bit dark , I'll adjust the exposure to make it a bit lighter".
Likewise if you take a photo of a full white card your camera will think "crikey that's bright, must darken that down a bit".
Yes - that IS how cameras talk :)

I just ran out to my garden and did just that.
These are straight out the camera jpegs from a Canon DSLR on Av mode.

The first one is of a pure black card - apart from the scuffs. It shows up as grey.



The second is the backside of the card - white. It shows up grey.



The third is a black piece and a white piece together. The average of the scene is ok here, as there is a 50/50 split so the camera thinks "ahhh spot on".




And here's the bits of card on the table in the garden.




Now you can start to understand when you take a photo of someone against a bright window, they come out as dark - almost silhouettes.
Likewise you try to take a picture of the moon in auto mode, with your eye you can see craters, shapes and texture, but your camera gives you a bright blob .

This is where you have to use exposure compensation.
If you're taking that photo of your pal in front of a bright window or a bright sky behind them, dial up exposure compensation by maybe 2 stops (+2).

I have to admit, I often have fun with folk at weddings with this principle. Knowing that as I'm setting up photos of the groups , or the bride & groom, and there will be loads of folk with cameras behind me... I'll put the sun right behind the subjects, in full on view of everyone's cameras and their auto mode cameras and phones will take a brain-flap and adjust the photo all wrong :)

Now this is the real basic simplified version of this.
Cameras are more complex with choices of metering modes, some will only meter from the centre spot, others will be heavily weighted to the middle 40% and so on... but the principle is the same. The metered section is going to be made grey by the camera.

Now think of poor me when I have a bride in a bright white dress... if she was in front of a white wall the dress would come out grey... if she was against a black wall, the dress would be blown out.
Now I'm a bit of a smart arse here as I shoot mostly manual with a light meter, or adjust with exposure compensation... but hopefully you can see what I'm on about.

And now we all know how everyone gets fantastic, colour sunset shots when you were with them and the sky was bright blue at the time :)

If you have any questions about this or anything else... gimme a shout.


G.x

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