WHAT DOES THAT MEAN?
Most photographs will have areas of dark and light, with shades in between. A wine bottle on a white background. A person sitting in the garden with blue sky, fluffy white clouds and dark shade under trees and bushes. Staff at their desk with white paperwork, dark chair, green foliage.
Digital sensors have limited latitude. A photo of a landscape may have a brightness range of 10 to 20 stops but can only correctly expose around seven stops (this changes with every camera and is getting better). In auto the camera chooses to 'throw away' what it thinks we don't want, in Manual, we choose what we want to keep or 'throw away' in detail.
Is it important to have a sky with detail?
Is it necessary to see what is in the shadows?
What is the most important thing in the photo? Correctly expose for that.
There is three exposure values in most images - black, white and middle grey. The colour of an image is categorised into these three areas. Middle grey is important - this is how your camera measures the light in a scene and then works out the settings. It will take all the values of the scene and average them out, ending up with middle grey. But obviously, not all scenes work this way. Snow scenes are mostly white. Night skies have a lot of dark. If you were to average these sort of scenes out to middle grey, the images would end up looking grey and murky.
One way of fixing this, in Manual or Auto, is by using centre-weighted or spot metering instead of matrix.
Centre-weighted - more emphasis on the middle of the scene
Spot metering - measures light in a certain spot. You need to know what you want to measure and make sure the highlighted focus area on your screen is on that spot.
Matrix - takes a reading from many different areas of the image and then compares with previous results.
These can work well most of the time, but in some instances, you need to take control. For example, if you are trying to photograph a glittering diamond on a bed of black felt, the camera will have trouble picking up that you want to focus and expose for the speck amongst all the black.
The sensitivity of the sensor to light. As you increase the ISO (higher number), the sensor becomes more sensitive to light. This means you can capture more light in your image.
Noise is the digital equivalent of grain in film. It appears as colour and luminance - speckles of colour (or white) and a gritty look. It increases as you increase your ISO or long exposures. DSLR cameras cope with noise the best due to their larger sensor.
File Quality - JPG or RAW
JPG is good if
you don't want to enhance further your photos
personal use where quality isn't as important
you want to get as many photos on the memory card as possible
you don't want to print (which I don't agree with)
RAW is good if
you want the best results
you are willing to do some post production on them
you want to use them in a commercial form
you intend to print images larger than 8 inches
You need to process RAW files on a computer with specific software. Creative decisions are made at this point to tone, contrast, colour temperature and exposure. Although I use Lightroom and Photoshop, cameras with RAW capability are normally sold with software for this.
Colour and White Balance
Each camera produces slightly different colours. No camera (or printer) can see the wide range of colours the human eye can see. If you capture RAW files, you retain the widest gamut of colours that your camera can record. If you save as JPG or TIFF, the camera will apply a colour space, usually sRGB (good for the web) or Adobe RGB (good for printing). During this process, colours outside the gamut will be changed to similar colours that are inside the colour space.
The colour of light changes throughout the day. Fluorescent and tungsten also have different colour temperatures. On a clear early morning and later afternoon, the light is warm. In the middle of the day, it is cooler - more neutral. If it is overcast, or there are heavy clouds, it is cooler still. Cooler light will be recorded as blue. Warmer light will be recorded as yellow/orange. Our eyes and brain adjust to the colour changes, and so does the camera. We have to either change it manually or let the camera decide what colour light it is (sometimes a fun idea to see what happens). Most cameras including the compact cameras have a range of settings for different light temperatures.