Nikon Coolpix A Optics

Fixed 18.5mm lens
Very good far-field performance from the Nikkor 18.5mm f/2.8 fixed lens.

The Nikon Coolpix A is equipped with a fixed Nikkor 18.5mm f/2.8 lens, with a 35mm-equivalent focal length of about 28mm. Construction consists of 7 elements in 5 groups, with a 7-bladed diaphragm providing an aperture range of f/2.8 to f/22.

Sharpness and contrast are very good at f/8 across the frame, and chromatic aberration isn't an issue (see below for more on that). Performance in the corners looks to be very good (but a little difficult to evaluate in this image), with just a hint of softening and very little coma distortion. Corner shading ("vignetting") is noticeable, but is fairly gradual so it's not too objectionable. See below for comments on macro, geometric distortion, performance wide open, chromatic aberration, etc.

The Nikon Coolpix A does not offer digital zoom, which is a bit odd for a fixed wide-angle lens camera, though you can usually do better by cropping and resizing as needed in post.

Macro
A larger-than-average minimum coverage area, with excellent detail. Flash exposure is uneven and overexposed in the center.

The Nikon Coolpix A captures a fairly large minimum area measuring 5.06 x 3.35 inches (129 x 85 millimeters) in Macro mode. Detail is excellent over most of the frame at f/8, though corners are quite soft. (Most lenses have some softening in the corners at macro distances.) Flash coverage is not very even, overexposing the center while leaving the bottom and right corners quite dim, so plan on using external lighting for macro shots at closest distance.

Geometric Distortion
Low geometric distortion.

The Nikon Coolpix A's lens produces only about 0.2 percent of complex barrel distortion, which is quite low, especially for a wide-angle lens. Uncorrected RAW files exhibit the same low distortion, which is a pleasant surprise. This is the tendency for the lens to bend straight lines outward (like a barrel -- usually at wide-angle) or inward (like a pincushion -- usually at telephoto).

Chromatic Aberration and Corner Sharpness
Low levels of C.A. (the camera suppresses it). The lens produces soft corners when wide open.

Chromatic Aberration. Chromatic aberration in the corners of in-camera JPEGs is low when wide open, exacerbated somewhat by softening, while the center of the image shows almost no CA. Stopping-down to f/5.6 or f/8 reduces the number of colored pixels, but they are more distinct. Still, C.A. is quite low in JPEGs.

Corner Softness. Wide open at f/2.8, the Coolpix A's lens exhibits strong blurring in the upper corners, though lower ones are sharper. The blurring doesn't extend too far into the frame, though, and the center is quite sharp. When stopped down to f/5.6 or f/8, all four corners exhibit good sharpness; almost as sharp as the center.

Corner Shading. The Nikon A's lens shows significant corner shading ("vignetting"), even when stopped-down to f/8, though it's fairly gradual as distance is increased from the center. Oddly, the Coolpix A does not offer any shading correction.

Lens Corrections

The only lens correction the Nikon Coolpix A seems to apply is chromatic aberration suppression, as geometric distortion and corner shading appear to be the same in uncorrected RAW files.

Chromatic Aberration Suppression

As you can see, lateral chromatic aberration is noticeably higher and brighter with in uncorrected RAW files, however it's still fairly low.


Overall, a very good lens when stopped down from maximum aperture. It's quite impressive that the Coolpix A is only suppressing chromatic aberration (as Nikon does in all its current DSLRs), and doesn't need to apply any distortion correction, though some (optional) corner shading correction would have been a nice feature.

Coverage
Excellent accuracy from the LCD monitor.

The Nikon Coolpix A's LCD monitor shows essentially 100% coverage in record mode. This is excellent performance, though not a surprise given its image is derived from the imaging sensor.