While the Nikon D800 is a very capable camera, there was one feature that got photographers more excited than any other, its 36-million-pixel sensor. This put it on a par with medium format cameras and even now, over a year and a half after its launch, it is still the highest resolution small format DSLR available.
And when the Canon 5D Mark III was launched a month after the D800, many photographers scoffed at its paltry 22-million-pixel resolution. Some dismissed it out of hand without even considering other aspects of image quality or its superb handling characteristics.
However, while 22 million pixels might be 12 million pixels fewer than the 36 million of the Nikon D800, it's also 6 million more than are found on the Nikon Df's sensor.
A key advantage of a good sensor with a high pixel count is that it can resolve plenty of detail. The D800 and its optical-low-pass-filterless friend the Nikon D800E make this very clear.
The often mentioned downside of having a very high pixel count is that the photoreceptors themselves have to be made smaller than on a sensor with a lower pixel count. This means that they receive less light and generate a smaller signal which needs greater amplification. As a result the images are noisier and it's more important to shoot at lower sensitivity settings.
There's also another drawback to a high pixel count that doesn't get mentioned quite so often. That is that the camera is more susceptible to image blurring from camerashake. Even tiny movements have a significant impact when the photosites are very small.
As a result we've found that if you're handholding the D800 you need to use a shutter speed of 1/125sec or faster to get images that are sharp at 100% on screen. In some instances this may mean that you need to push the sensitivity up a stop or two and accept that the image will be a bit noisier than you might have wished.
Meanwhile if you're using the camera on a tripod, you need to use a remote release and engage mirror lock-up or exposure delay to avoid shake from the mirror blurring the image.
Some may argue that these issues only come to light when you pixel peep, but if you're paying for a 36-miilion-pixel camera you expect to be able to get the full benefit of them.
As well helping to keep noise levels down, having a lower pixel count means that any tiny accidental camera movements are less significant, so the camera produces (smaller) images that look sharper at 100% on-screen.
With many cameras now topping the 20-million pixel mark we have started to use the word 'just' when describing sensors with 16 million pixels. It's a popular count for the Micro Four Thirds format, but we forgive it because it is a little restricted by its smaller sensor size, plus cameras like the Olympus OM-D E-M1 are very capable.
The Nikon Df is a comparatively small and light full-frame camera. It is weatherproof and designed to be used outside on treks and adventures. And while it can be used on a tripod, those who buy it to travel light are less likely to want carry a tripod, so it will probably be used handheld most of the time. Consequently, it needs to offer the ultimate in low light capability and noise control.
By plumping for a sensor and processing engine that is used in its top-of-the-line SLR, the much-respected D4, Nikon has given prospective owners of the Df a clear signal that it is a high quality and capable camera. It should also be a model that can be pushed to the limits of low-light shooting with a top expanded sensitivity setting of ISO 204,800.
There are plenty of valid reasons why the Nikon Df should have a sensor with 16 million pixels. But would most prospective owners like it to have a 24-million pixel sensor like the Nikon D610?