More Mega Pixels is Not Always Good

Do not fall into the marketing trick of thinking that more mega pixels is better! There is a reason that the Canon’s top model, the Canon 1Dx, “only” has 18 mega pixels.

A lower pixel count gives the following advantages:

  • Better light sensitivity (less noise in images)
  • You can make due with a much less expensive lens with less resolution (if you have less than 16 mp).
  • The ability to burst fire more shots per second (less data to transfer).
  • More images can be stored on your card, and storing them on your PC requires less space.

Lens Resolution (MTF)

At 16 mega pixels you will need an fairly expensive lens to get the images sharp (for an explanation of MTF see here).

The following picture could have been taken with an entry level DSLR if a good enough lens is used. Why? Because in a studio we control the lighting and only need ISO 100, and even entry level DSLR cameras don’t have a lot of noise at ISO 100.

If we crop in at 100% you can still see the details in the hair and skin:

It was taken with a 9 year old Canon EOS 1Ds Mark II with the very impressive “Canon 70-200mm f/4 L IS” lens, but as mentioned you don’t need more than an entry level DSLR to get these results (under these circumstances) if you have a sharp enough lens. If you can’t get these kind of results (or better), then borrow a lens from a friend and be amazed at the difference. Unfortunately this will mean that you will have to pay for an expensive lens instead of a cheaper camera upgrade :-)

  If you don’t have a very good lens you have no reason to go beyond ~8 mega pixels. You will get blurry images anyway.

My Canon 28-105mm all-round lens was great when I had the 8 mp Canon EOS 20D, but it gave stomach turning blurry results on a 16 mp camera. I simply had to give it away! It was even blurry in the center of the lens!

Noise Levels

The bigger the sensor, the easier it is to make it more sensitive. Imagine a sensor that detects a single pixel:

It is like filling buckets with rain water – it goes faster with larger buckets. Because less photons hit the smaller sensor they will have to amplify the signal to get the same amount of light registered. So the noise level will be higher for the small sensor, as the amplification not only amplifies the signal, but also the noise.

This is why full frame sensors, that are just as big as the old 35mm film roll frames were, are much more light sensitive when comparing with sensors that have a crop factor (meaning that they are smaller than the 35mm film roll frames).

It is of course cheaper to have a smaller sensor, as it uses less materials, and it is less prone to errors during manufacturing, which is why you only see full frame sensors on semi-professional cameras and up, like the Canon 5D Mark III or the Nikon D800.

Okay, so what does this have to do with mega pixels? It is quite simple: the more mega pixels the sensor registers, the less area is available for each pixel, meaning that it will not be able to register as much light. See the following illustration:

Both sensors have the same total physical size, but because the one on the right has 4 times less pixels, then each of those pixels are going to get 4 times the amount of light.

They make advances in technology all the time, and this is why you cannot compare directly between cameras and conclude that one camera will be more light sensitive than the other just by looking at the mega pixel count and sensor size alone, but it does give you an indication of the light sensitivity (with the date of the technology in use).

The above is very simplified. The pixel sensors usually sensors Red, Green and Blue sub-components arranged in a pattern where the Green component is most accurately recorded as our eye and brains are more sensitive to green (jungle life adaptation perhaps):

 

But let us not go into too many details here, as we are more interested in the number and size of pixels – not how they are arranged.

So if someone has a smartphone camera with a really tiny sensor and cheap lens that records 40 mega pixels, then you know without a doubt that it will be very difficult to take pictures in low light with it, and it will be difficult to take sharp pictures if you zoom in at pixel level.

Do not get blinded by numbers. Look at sample images in low light conditions. I bet you will prefer 8 mega pixels that are razor sharp rather than a blurry 16 mega pixel image. If you think an iPhone or another smartphone takes great pictures, then take a look at your pictures are 100% – if you still think it is great, then by all means do NOT buy a DSLR – you already have enough quality to satisfy your needs, so there is no need to upgrade.