Huge apologies, for some reason the post about histograms didn't publish and so here it is - thank you to Edward - from one of my training courses at Spetchley gardens for letting me know, much appreciated.
You probably know that you can check the exposure of the shots you have taken simply by reviewing them on your camera’s LCD screen. The problem is that often by looking at the picture alone on your LCD screen you can be mislead and so you may think it looks ok, but there is a better way to check. If you know how to read the Histogram on your camera it is the most important thing you can do to ensure a good exposure.
Your camera gives you the option to show the range of brightness in your image as a graph, which plots the light levels from jet black, on the left, midtones in the middle and pure white, on the right.
A ‘perfect’ histogram rises gently from the left, rises in the middle and drops on the right, indicating a full range of tones but no loss of detail in shadows or highlights.
If shots are too bright, the graph will look all bunched up at the right hand side, suggesting burnt-out highlights.
However, if the shot is underexposed, the graph will be all over to the left. In both cases, such patterns suggest exposure compensation might be necessary.
Remember when you burn out highlights there is no information for that area saved and so this is not something you can pull back in photo shop, and likewise if the image in underexposed there will also be no information to pull out in photoshop. If it is bright sunshine on your camera LCD looking at your histogram can be easier as you will see if there is a nice gentle curve on the histogram or if everything is extreme to one side or the other.
So when you look at your histogram, the left hand third of the graph shows the shadows, the middle third shows your midtones and the right hand third shows your highlights.
Not all scenarios give a histogram that fits perfectly along the width of the graph. With low-contrast scenes, the histogram won’t reach both extremes of the graph.
With high-contrast scenes, the graph will look squashed towards both sides. In these cases, expose so that the right-hand side of the histogram is placed as far right as it can go without being ‘clipped’ – you’ll retain detail in the brightest highlights.