Welcome to the PhotoSkill Digital Photography Guides;

Number 1: Exposure.

                                                                                           


The Black, Grey and White spaces above could represent any subject, Black, Grey and White horses, cats, pieces of card, whatever.

1) Remember: Exposure is determined by the light falling on a subject.

2) BUT!... cameras do not read the light falling on the subject...Cameras read the light reflected from the subject. The maximum - the brightest part of the subject, or highlight -  in a normal subject without a mirror or other highly reflective subject would be about 96% of the light falling on it.

3) Many general subjects reflect an overall average of 12% (often quoted as 18%, but don't worry about this) of the light falling on them, so cameras and their light meters are programmed to give exposure based on this.

4) As the camera is assuming that every scene it 'sees' is reflecting on average 12% of the light falling on it, then the Black 'subject' above left will provoke a long exposure to get enough light in to create 12% grey, the 12% Grey 'subject' will provoke 'correct' exposure and the White 'subject' will provoke a brief exposure as enough light to create 12% Grey will quickly enter.

5) The 'correct' exposure for each is, in fact, the same.

If the camera should read, say, 1 second at f8 for the Grey subject, then as you shoot the black subject at 1 second / f8  much less light comes in as the subject is black and Hey! guess what? ...the image is black. As you shoot the White subject for 1 second / f8, lots of light comes in, and you have a white image, which is, of course, as it should be. When it is on Auto your camera is altering the exposure all the time on the assumption that everything it 'sees' is 12% of the light falling on the subject, remember?.

6) You can easily show this yourself with your digital camera set to Auto or P(rogram) by taking shots (all in the same light) of:
a) a black,
b) a dark-mid grey
and c) a white subject.
Be sure to fill the frame with the subject only and without casting your own shadow on it.

7) What did you get? A black, grey and white image? Or 3 grey images?

8) Then take the reading from the dark-mid grey subject, but this time set the indicated reading manually, that is, with your camera set to Manual. Re-shoot all three subjects, all in the same lighting, and heyyyy!, they appear as they should, black, grey and white.

9) Now you should have the basic mystery of exposure demystified! 

10) You will find a collapsible 30cm grey card/focussing target and white balance/reflector  in the PhotoSkill listings!