Wetpixel Field Review: Nikon D500

Image Quality

The D500 has a Sony Semiconductor APS Exmor 20.9 MP sensor, which features copper wiring in its data lines, designed to increase readout speeds. However, Nikon seems to have also tweaked the sensor, meaning that it’s performance is better than that of other Sony 20MP sensors. While comparison with other Sony sensors is useful, it is important to note that the D500’s is not an “off the shelf” Sony component.

The actual sensor size is .93” x .61” (23.5 x 15.7mm) with an individual photosite size of 4.22 microns. This is slightly larger than than the D7200 (3.92 microns) and smaller than the D810’s (4.88 microns). Photosites are the actual areas that light strikes and generates image data. In practical terms photosite size is an indication of low light performance. As light photons strike the sensor randomly, larger photosites tend to be more accurate and hence generate less noise. This is why large sensor cameras typically have better low light performance then ones with smaller sensors. However, as Thom Hogan points out:

“Given that the D500 with its smaller photosites performs so well compared to older Nikon DSLRs with larger photosites shows just how fast technology has changed in the sensor world.” (1)

Resolution as a measure of camera performance is also perhaps somewhat redundant. Almost all modern cameras (and many smart phones!) can provide sufficient resolution to capture amazing imagery. In addition, as underwater photographers we cannot often completely control lighting conditions or water clarity. Indeed, the simple fact that we shoot through water limits image quality more than the technology or sensitivity of the sensor.

Very high resolution can also introduce other potential issues, including limiting lens choices and generating very large file sizes.

Hence as underwater photographers, resolution should be seen as a compromise and not a rigid definition of camera suitability.

20MP sensors can deliver an image sized at 30 x 40 inches (76 x 102 cm) in native resolution and software can produce images at pretty much whatever size required.

In common with all cameras, the D500 suffers from diffraction somewhat. Simply put, as the light moves through an aperture ring, some of it “catches” on it and this causes a ripple effect. In turn, this causes some light to fall onto adjacent photosites, which causes image softness. The wider the aperture, the less diffraction occurs. Nikon’s D800 Technical Guide specifically notes that diffraction effects occurs at apertures smaller than f11.

Thom Hogan (3) notes that to get optimum edge sharpness with the D500, f8 is optimal and beyond f11, there is some edge softness that is apparent when images are significantly enlarged. For comparison purposes, Hogan finds that the D800 starts to lose visual acuity at f5.6 (4).

Of course, these numbers have to be balanced against the required depth of field and corner sharpness behind a dome.

Underwater, the D500 produces very pleasing images straight out of the camera, with sharp details and vibrant colors.

Being able to use the Tokina 10-17mm f3.5-4.5 again confirmed just how convenient this lens is for underwater use.

The DX sensor delivers a 1.5 times crop factor which makes wide-angle lenses less wide and macro lenses more magnified. It also means that depth of field is increased by around one stop. The latter makes producing wide angle images with acceptable corner sharpness easier when behind a dome and removes some of the need for high ISO performance.

Dynamic Range

Wide angle underwater scenes often contain a huge number of tones, from bright surface to dark depths. An image of a manta passing overhead, puts the camera in the difficult position of trying to capture the bright sunshine and the creature’s silhouetted shape.

Traditionally, it was widely believed that digital cameras were less capable of capturing scenes with a large dynamic range than film ones. Certainly, careful framing was required to avoid actually seeing the sun in an image. However, sensors have improved and the D800, along with careful technique, allowed the reintroduction of the sun into underwater images.

The D500 is the first Nikon Pro DX camera to have been released since this, so it is interesting to see how it copes with sunballs and other high dynamic range images.

Another important element is the ability to open up parts of the images that are underexposed in post. Recovering detail from the shadow areas of an image is very much a performance enhancement that has accompanied new carmera releases.

1. Introduction and Acknowledgements.
2. Image Quality and Dynamic Range.
3. ISO Performance and Autofocus.
4. XQD Cards, Build, Controls and Power and Speed.
5. Alex Mustard on the D500 and Conclusion.