Why you should care about sensor size

A comparison of common camera sensor sizes

This is an illustration of the most commonly used sensor sizes on the market.

 
In my opinion, the technology in the camera is not worth talking about unless you can actually see fairly obviously how it makes a difference. Fortunately, it is quite easy to see the effects of sensor size.
 

There are two very common failings of small, compact camera sensors:

 

Blown highlights
 

Have you ever been annoyed with this in one of your pictures? This is caused by a lack of dynamic range. You see, there is only a certain range of darkness and brightness that a sensor can detect. If the sensor has a smaller dynamic range, it cannot distinguish the very light colors from the very very light colors, and thinks that it is all solid white. You then end up with the ugly complete white sky like the picture above. This is called blown highlights and occurs with small sensors. Larger sensors are much more likely to preserve the highlights, ending up with much nicer skies, as a result of their greater dynamic range.
 
High ISO noise

 
This is the noise pattern caused by the small sensor at high ISO’s. When a higher ISO is set on the camera the sensor is told to produce an image with less light. Go from ISO 100 to 200 and you are telling the sensor that it should produce an image using 50% less light. Guess what? The image it delivers won’t be as good. Now couple this with a sensor that was already receiving only a small amount of light to start with, and the results are not pretty. This is where a full frame DSLR sensor has the advantage, and allows you to increase the ISO massively without seeing too much image quality degradation.
 
But why the difference?


Look at the first picture and compare the size of the sensors. Nowadays, you can find 12Megapixels packed into any one of the sizes illustrated above. So, the sensors have the same amount of pixels, but the largest sensor is 31 times larger (in terms of area) than the smallest one. Of course, since the pixel count is the same (12MP) the individual pixels have the same area ratio.
Think about this.
If one pixel gets 30 times more light than the other, is it surprising that it produces better image quality? That is what it’s all about, the larger the sensor, the more light information it has to play with.
 
It’s not about the number of pixels, it’s about how good each pixel is


A larger sensor with the same number of megapixels will give you better image quality than a smaller sensor. While the wonders of minituarization has allowed us to put a camera in every phone produced these days, there is no getting away from the laws of physics. Even though they may have as many megapixels as their bigger brothers, these small sensors only have a tiny amount of light information to work with. So it’s no wonder that the pixels that they deliver are not as good as real cameras.
 
Which size sensor should you consider?
 
There are mainly two considerations for this:
 
1. Size / Weight
 
The trend is pretty obvious, the larger the sensor, the larger the lens, the larger the whole camera.
If you want to have a camera that you can put in your pocket, you obviously have to go with a small sensor camera since only those are small enough. So no need to think about all this then?
Not exactly. You now know that image quality is primarily a question of sensor size, so at least keep this in mind when you are shopping for a small sensor camera. The manufacturers will try to market things like: “This one with the titanium body, yes, it is sooo much better than that plastic one, yes sir!” Yes, it costs twice as much but if the sensor sizes are the same, maybe you should think twice about whether it really is better.
 
2. Budget
 
Obviously, the larger the sensor, the more expensive it is, etc. etc…
If you don’t mind carrying it around, get the largest sensor you can afford. I personally think that entry level DSLR’s are an excellent compromise in terms of image quality, size and price. The prices have really come down in recent years, and the image quality is on a different planet compared to compact cameras.


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