We’ve become used to Nikon DX (APS-C) format DSLRs having 24 million pixels so some photographers may be asking why the D7500 has just 20.9 million pixels. However, this is the same pixel count as the D500 announced back in January 2016 (in fact it has the same sensor) and it’s done to boost speed and low-light capability.
It’s interesting to note that the Nikon D5, which was announced at the same time as the D500 and is a full-frame or FX format camera, has an effective pixel count of 20.8 million. If the D500 and D7500 sensors were scaled up to match the physical size of of the D5’s sensor they would have an effective pixel count of around 48.6 million. So actually a 20Mp APS-C format sensor is quite densely populated.
The key reason that Nikon has restricted the D500 and D7500 sensor to 20.9 million is to enable the photoreceptors, often called pixels, to be larger than they would be on the 24 million pixel sensor. Having larger receptors enables them to be receive more light so they generate a stronger image signal than a higher-resolution sensor.
Weak image signals require more amplification, and just as when you turn the tv or music player volume up high, this introduces distortion or noise. A strong signal requires less amplification and is therefore cleaner, in other words, the images from the the D7500’s sensor should have less noise than those from higher resolution cameras like the D7200.
I spoke to Jeremy Gilbert, Marketing Director for Nikon Northern Europe, about the D7500’s pixel count and he said, ‘people asked the same question about the D500, it’s to be expected, but the D500 answered those questions through the image quality that it produces and all the awards that it has won’. It’s a very fair point, as our Nikon D500 review explains, the D500 produces very high quality images.
Enabling the D7500 to produce a cleaner signal than the D7200 means that Nikon has pushed the standard sensitivity (ISO) range up one stop further, while the expanded range peaks at the same ISO 1,640,000 high as the D500. This upper value may largely be for attention-grabbing purposes, but the important thing is that the images a lower down the ISO range are better quality with lower noise. Settings such as ISO 3200, 6400 and 12,800, which are useful in everyday situation produce more usable images.
Another advantage of using a lower pixel count sensor for the D7500 is that there’s less data for the processing engine to handle and this will be a contributing factor to the 8fps (frames per second) maximum continuous shooting rate.
It also means that the buffer doesn’t fill up quite as quickly and hence the D7500 can shoot at 8fps for up to 100 Large Fine jpegs or 50 14-bit uncompressed raw files.