Studio Tests (DX format)

The Nikon 58mm F1.4 gives somewhat mixed results in the lab tests. It's not very sharp at all wide open, and needs to be stopped down to F5.6 - F8 to get really good results across the frame. But in all other respects (chromatic aberration, vignetting and distortion) it performs extremely well. From these tests alone, though, it's difficult to see much obvious advantage when comparing it to the AF-S Nikkor 50mm f/1.4G.

Sharpness Sharpness is unimpressive at F1.4. The centre of the frame improves quickly on stopping down, though, giving excellent results at F2.8. However the corners lag somewhat behind, and only really sharpen up fully at F8.
Chromatic Aberration Lateral chromatic aberration is very low, and unlikely to be very visible in normal use.
Vignetting Vignetting is negligible, as usual for a full-frame lens used on DX format.
Distortion Distortion is extremely low, with just a little barrel-type visible if you look closely. It's unlikely ever to be a problem in real-world shooting.

Macro Focus

Macro (DX) - 170 x 113 mm coverage
Measured magnification: 0.14x
Distortion: Slight barrel

Minimum focus distance*: 54cm
Working distance**: 34cm
Focal length: 58mm (87mm equiv)
* Minimum focus is defined as the distance from the camera's sensor to the subject
** Working distance is measured from the front of the lens to the subject

The 58mm wouldn't be our first choice for close-up work. It offers a maximum measured magnification of 0.14x, which isn't atypical for a fast prime, but is distinctly unremarkable in the grand scheme of things. To be fair, though, this isn't really what the lens is designed for anyway.

As tends to to be the case with fast primes, image quality wide open at minimum focus is nothing to write home about, and the lens has to be stopped down to F2.8 to get decent sharpness even in the centre of the frame. At this point the corners in our flat-field chart test are still extremely soft, and the lens has to be stopped down to F8 for them to sharpen up properly. This likely reflects curvature of field as much as anything else. Even so, if you're looking for a lens to shoot close-ups, this isn't it.

Specific image quality issues

As always, our studio tests are backed up by taking hundreds of photographs with the lens across a range of subjects, and examining them in detail. This allows us to confirm our studio observations, and identify any other issues which don't show up in the tests. Here we're looking at issues specific to DX users; for a fuller picture, be sure to read the next page too.

Sharpness at large apertures

The test data shows that the 58mm isn't especially sharp wide open, and needs stopping down to give best results. This isn't unusual for a fast prime, but it comes as something of a surprise from such an expensive lens. However the graphs alone don't tell you how your pictures will actually look, so here we'll show what you can get from real-world images.

The rollover below shows how image quality progresses through the aperture range, using the Nikon D7100 as the test body. The camera was placed on a tripod, and the lens was focused using magnified live view. We can't stress enough how absolutely critical correct focusing is in getting properly-sharp results from this lens - at 58mm F1.8 on DX, depth of field is vanishingly slim. Images were shot in Raw, and processed using Adobe Camera Raw with lens corrections disabled. We're showing 100% crops from the centre and edge of the frame, upper and lower right respectively. Click on any image tow download the full-size version.

F1.4
F2
F2.8
F4
F5.6
F8
F11
F16

At F1.4, the 58mm is visibly 'soft' even in the centre of the frame, with the hard edges of the 'M' looking somewhat ill-defined and the overall image appearing just slightly 'hazy'. Technically, this is most likely due to residual spherical aberration. However the lens is still resolving a lot of fine detail and texture, just at rather low contrast. The image sharpens up quickly on stopping down, and the very best overall sharpness comes from F4 to F8. Diffraction softening starts to become visible at F11, and becomes quite visible at F16 if you look this closely.

Most subjects are rather more three-dimensional than this, of course. In practical use, F1.4 is also much more likely to be used either for shallow depth of field, or shooting in low light. Absolute pixel-level sharpness isn't necessarily the only consideration for either, in terms of overall image quality (or even necessarily the most important one). For selective focus work, the main pictorial impact comes not from how sharp the in-focus regions are, but from the contrast between them and the out-of-focus areas of the frame. Meanwhile at high ISO, you'll probably just as much detail to noise as to lens aberrations - and a fast lens lets you keep noise ISO speeds, and hence noise levels, down.

Below we show a selection of real-world examples taken wide open on the D7100, with 100% crops taken from the point of focus. In the selective focus shots, the lens is resolving fine detail in the focus plane, but again at distinctly low contrast. But the overall image quality is dominated by lens's beautiful rendition of the out-of-focus areas of the frame.

D7100, 1/160sec F1.4 ISO 140 100% crop (camera JPEG)
D7100, 1/200sec F1.4 ISO 100 100% crop (camera JPEG)
D7100, 1/160sec F1.4 ISO 2000 100% crop (RAW + ACR)

In the third example at high ISO, the camera and lens have between them given a quite usable image when shooting handheld in very low light, but any really fine detail gets swamped by noise. In this particular scenario you'd quite possibly get better results shooting with an image-stabilised 17-50mm F2.8 zoom, relying on image stabilisation to shoot with a slow shutter speed - but that wouldn't work with a moving subject.

Autofocus accuracy

The bigger problem we had when using the 58mm on the DX format D7100 was with autofocus accuracy. Out of the box, the lens focused reasonably accurately at the kind of 'portrait' distances (~2 - 3m) that we'd most commonly use an 85mm-equivalent lens for, and with AF Fine-Tune to correct for slight front-focusing (correction value -2), it was essentially spot on. So far, so good.

The problem came when focusing on more distant subjects, where we consistently experienced significant front focus. This could in principle be corrected with a larger AF Fine-Tune correction, but then close focusing was thrown out. So we ended up having to choose one distance range for which the lens could focus accurately wide open, and accept inaccuracy at longer distances. This misfocusing could be eliminated by switching the camera to live view and using sensor-based contrast detection AF - but this is slow and hesitant at best, so it's far from ideal for frequent use.

D7100, F1.4, ~ 3m 100% crop at point of focus
D7100, F1.4, ~ 50m 100% crop at point of focus

In these examples, the camera has focused accurately on the relatively close fountain (and did so consistently across five replicate shots). But switch to a more distant subject and the camera consistently misfocused - the AF point was placed on the sculpture's head, but the tail has ended up in sharpest focus.

To be fair we didn't see this kind of behaviour on the full frame D800, which (after AF Fine-Tune) could focus the 58mm accurately at all distances. It's impossible to say whether this problem would affect anyone else using this camera / lens combination, either. But it does highlight the fact that the phase detection AF systems used by SLRs for normal shooting just aren't sufficiently reliable with fast lenses. This is now a pretty stark disadvantage in comparison to mirrorless cameras, which have no such problems as they focus using the main image sensor.