Understanding how the innards of your camera function can help you understand how or why your photo is coming out under or overexposed on any given day.

You sensor is the most important part of your camera…yes I know – the sensor would be nothing without the rest of the team – but your sensor is the bit that catches the light and turns it into a picture.

Think of your sensor like this:

Picture in your head – your photograph lying on a table. Your photograph represents your cameras sensor. Now on top of each pixel that makes up your picture, put a tiny bucket. When you cameras shutter opens – these buckets (which are real little buckets on your sensor that are called Photosites) start to fill up with light (photons).

Some areas, in the scene you are photographing, have more light than other areas so the buckets capturing those areas will fill up with a lot light and might even start to overflow!


Any bucket that fills up with no light (or not enough light to reach the threshold) will be black on your photo and a bucket that is full to the top will be white on your photo. All the colours in between are different full levels in your bucket. (representing darker or lighter versions of that colour in between black and white).

What happens when one of your buckets (photosites) overflow with light (photons)? Well obviously the pixel that is represented by that bucket can’t get anymore white than it is (white is white), but the light carries on trying to collect in that bucket and the bucket ends up overflowing and splashing into the buckets around it and messing up their correct ‘level’ of the colour light they are collecting. The more the buckets overflow the more chance you have of an overexposed picture.

Now that your sensor has collected all the photons into the photosites and the shutter is closed – What happens to these buckets (photosites) full of light? The information collected by the photosites is converted from analogue information to digital information so that your camera can understand it.

… (a simple way of explaining…) the buckets of light are ‘weighed’ and each weight is converted into bits and bytes. (0’s and 1’s) Like your computers binary code.

Those bits and bytes are then saved to your memory card and you camera is then ready to take the next photo.

Now think about this: how many photos can your camera take per second? So how fast is this entire process? Incredibly fast!