Why less pixels can be better.

Aaaah melted snow freezing during the night...I dedicate this one to everyone who'll break a leg today in Dublin :)

Anyway, today's post is to mention a trick when picking a digital camera: if you care about ISO noise (you want less), avoid sensor with too many megapixels. But why?

In order to shoot in low light, you increase the ISO number on your camera. On film cameras, it used to be the ASA number of the film, i.e. the amount of light sensitive chemicals put on the film. On a digital camera, photons don't hit a film, they hit a pixel sensor. If they deliver the sufficient amount of energy, it triggers that pixel to send a message to the camera "hey, I received a blue photon, I'm a blue pixel!"

In order to make higher ISO, we just tell the pixel to trigger a signal even when receiving very little photons. And there comes the noise: at high ISO, the sensing pixel is asked to be very "trigger happy", and sometimes sends a message even though it did not receive the corresponding photon. Therefore you have digital noise : a blue, red or green pixel where there shouldn't be.

Digital noise at ISO 52000 on a D3S.

Now look at those 2 schematics to understand why less pixels can mean less noise too:

Given that most sensors are the same size, if you have less pixels, the surface per pixel is larger, allowing the pixel to receive more photons and therefore, be less likely to make a mistake.

So this is how you should make your final choice:
  • if you care about max printing size go for more pixels
  • if you care about low light photography, go for less pixels.
This is why Nikon's top range cameras consists of the D3X and the D3S: same cameras, one for low light junkies, the other one for printing junkies :)

Would I recommend a compact /DSLR that his performing well in higher ISO? Yes indeed!
  • Canon's S90 and S95 have a larger sensor than most compact and limit themselves to 10MP (trust me, you will never print something that requires 10MP if you own a compact).
  • On the DSLR side: Nikon rules the high ISO world/ D7000 and D700 perform the best, and then of course the D3S...if you can afford it.
  • Finally in the world of rangefinder yet unaffordable cameras, the Leica M9 is exceptional in the high ISOs.

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