A few years ago, just about every Nikon DSLR captured images at around 12 megapixel resolution. The main differences between camera models, then, involved features (speed, AF) and sensor size (FX vs. DX). The biggest advantage of the FX sensor cameras at that time was sheer low-light performance. For the most part, my colleagues and I agreed, the megapixel race seemed over, or at least, diminished as an important feature.
Over the last year, Nikon has been steadily upgrading their entire camera line to 24+ megapixels. Even the low-end Nikon D3200 has a 24MP sensor. In fact, there are only three cameras in Nikon’s current line-up that don’t offer at least 24MP: the D300s (12MP), D7000 (16MP) and D4 (16MP). This had me scratching my head a little, as I certainly know from experience that a 12-16MP camera easily delivers the goods in most situations.
Why those pixels matter
A camera’s megapixel count is a measure of its resolution. However, cameras differ in terms of image quality, and lenses can also impact the ability of a camera to resolve fine details. When most of us think about reasons for why we’d need (or at least, want) more megapixels, the answer is usually:
- I want to print really big
- I want to be able to crop in on my images without losing detail
Ironically, most photographers just aren’t printing that large these days. Most enthusiasts I know are printing 12×18′ (on Super-B paper) at the largest, if they’re even printing at all. So here we are in an age where we can get a 24MP entry-level camera and yet we aren’t using it to print big! The other point, cropping, is certainly valid. However I fail to see the point of using a 24MP camera just so that I can be sloppy with my technique. Besides, the overhead of 24-36MP pixel files is such that in most circumstances, I don’t want to shoot in such a way that I’m just throwing away half the pixels each time. My personal philosophy is that if I’ve got 36MP, I want them to cover the subject as much as possible!
So that brings us back to today’s situation. 24+ megapixel cameras for photographers who generally make small(ish) prints. And here’s where those extra pixels suddenly come into play. If we examine our images at 100% magnification, you can examine fine-grain detail and also noise. The conventional wisdom is that camera sensors with larger photosites (like the Nikon D3s or D4) will have better low-light performance than their high-megapixel cousins. And at 100%, this is pretty much true, as shown in this comparison.
However, things get different when you print. At a typical 240ppi print resolution, a 12×18″ image has pixel dimensions of 4320 x 2880, or about 12.4MP. That means for a 12MP camera, you’d be printing at around 100%, but for cameras with more resolution, you’re actually shrinking the image to print it. The Nikon D800 has a native resolution of 7360 x 4912 pixels. To get a 12×18″ print, you’re shrinking the image by about 42%. The end result is that the final print won’t show as much noise or grain as you’d expect. In fact, you’d be surprised to see how good even high-ISO images can be when printed at “traditional” sizes.
The take-home message is that unless you crop your images severely, a 24 or 36MP image can be just as good at high ISO as images from a camera with fewer but larger photosites. Tone and color transitions can look cleaner, too. The primary reason for a camera like the Nikon D4, then, is to deliver speed when throughput is critical. At 10fps continuous shooting, the Nikon D4 is still the undisputed action camera from Nikon. So if you’ve been hesitant to upgrade to a high megapixel camera because of ISO concerns, don’t worry. Just make sure that you have plenty of memory card space and a fast computer to process those images!