How to measure your cameras ability to capture different tones.
When you look at the histogram on the back of your camera, can you visualise what those spikes actually mean in terms of relative tone? This simple experiment below will tell you just how dark you can shoot before you lose details in the shadows and just how light you can shoot whilst retaining some texture.
Firstly, find yourself a neutral coloured piece of textured cloth (something like a white or grey fluffy towel will do nicely).
Hang it on a fence/chair or somesuch in constant lighting (sunny days where the towel is evenly lit are perfect).
Spot meter on the towel and set your camera (in manual mode) so that the meter is in the middle, that is will render the towel as middle-grey. Take a shot. The spike from the towel should be in the middle of your histogram (slightly to one side or the other is fine).
Now take a series of shots allowing more light into the camera each time until the towel is completely over-exposed and flashing away like a police car in a high-speed chase.
Reset the camera back so that the meter reads middle-grey. Take a shot and this time take a series of shots allowing less light into the camera each time until the towel looks pitch black and the spike is flat to the left of the histogram.
Upload these shots into Photoshop (or similar) and make a composite (stepwedge) where the middle-grey shot is in the middle and you have a series of darker and lighter shots either side of it. Make a note of:
Where do the highlights start to lose detail
Where is the towel approaching pure white
Where do the shadows start to lose detail
Where is the towel approaching black
You should see something like the following:
+2 stops, white towel still has a hint of detail, +2 2/3rds is white.
-3 stops the dark greys start to lose detail, -4 stops is near-black.
I hope that this helps you pre-visualise the relative difference between tones and that you now know what 2 stops of difference actually looks like in terms of shades of grey. You can make marks on the back of the camera (a sticky label or screen protector with marks on) that will show you where the different tones are relative to the histogram spikes, this is far more accurate than trying to guess from looking at the picture on the screen.
