How to buy a camera: how many megapixels do you need?
The megapixel count is often the first thing consumers consider when deciding to buy a camera. But are high sensor resolutions really that important, and is there a catch?
How much resolution is desirable? The first consumer-level DSLRs had sensors capable of producing images of about 6Mp in size. This seems tiny by today’s standards, but even this was plenty for producing decent A3-sized prints.
The smallest pixel count you can expect from a current DSLR is 12.1Mp. Nikon, in particular, is pushing the boundaries with its new entry-level DSLR, the Nikon D3200, which boasts a class-leading 24.2Mp; and its latest full-frame offering, the D800, which weighs in at a whopping 36.3Mp.
After years at the top of the pixel charts, Canon is now playing catch-up, with its APS-C range offering pixel counts from 12.2Mp (for the 1100D) to 18Mp (for the 600D, 60D and 7D); and its full-frame cameras offering 16.1 pixels (for the 1D Mk IV) to 22.3Mp (for the new 5D Mk III).
That said, Nikon’s flagship full-frame DSLR, the D4, which retails for a cool £5k and change, offers just 16.6Mp, which suggests that size isn’t everything.
Images with higher resolutions enable tighter cropping, so for example, if the lens you’re using won’t give you enough telephoto reach, you can take your shot anyway and cut out just the section you need.
Even so, there are dangers with this, as very tight cropping places much greater demands on lens quality. This is because any lack in sharpness or the presence of chromatic aberration (colour fringing) will become more noticeable.
Higher resolution photos inevitably mean bigger file sizes, especially if you shoot in raw quality mode to enable corrections to exposure, white balance and picture style (colour and contrast options) at the editing stage. For example, a typical raw file from an EOS 600D or 7D can be around 25Mb in size, whereas the same image might only be about 10Mb from a Nikon D90 or D300S.
This not only means that your memory cards will fill up faster, but also that the camera can slow down in a shorter space of time when shooting in continuous drive mode. This is because you’ll have to wait for the camera’s internal memory buffer to clear to the memory card.
To squeeze more pixels onto a sensor that has the same physical dimensions, each ‘photo site’ needs to be smaller, and can therefore capture less light. The trade-off for higher resolutions is often an increase in digital image noise, which gives pictures a grainy appearance, especially when shooting at medium to high ISO settings.
The latest sensor designs aim to minimise the gaps between adjacent pixels, coupled with advanced in-camera image processing to smooth out the noise.
PAGE 1: Overview of how to buy a camera
PAGE 2: Body design and new DSLR features
PAGE 3: How many megapixels do you need?
PAGE 4: DSLR video options
PAGE 5: What you want in a viewfinder
PAGE 6: How fast should your new DSLR be?
Bracketing Explained: what you need to know about maximising detail in your photos
Don’t bide the dust: a perfectly safe guide to sensor cleaning
Manual focus: what you need to know to get sharp pictures