DxOMark review for the Nikon 24-120, the new constant f/4 aperture on DxOMark.

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DxOMark Lens

Introduction

The construction of the lens has also been improved and refined: if it still counts 13 groups, the number of optical element now reaches 17 (15 on the old model). For this lens, Nikon used its Nano Crystal Coat to reduce or eliminate internal reflections and thus to annihilate parasitic phenomena such as flare or ghosting effects.

To build this zoom, Nikon used two ED (Extra-low Dispersion) and three aspherical lens elements aiming at reducing aberrations. While the previous 24-120mm also used two ED lens elements, it had only two aspherical ones and no Nano Crystal Coat.
 
Combined with the constant f/4 aperture, the use of Nikon’s VR II stabilization technology promises to save up to 4 shutter speeds. So although this is not really a fast lens, the addition of these two features (constant aperture and stabilization) should help you capture sharp pictures in complicated light environments
Let’s jump to the tests.

Much more light

As expected, all these improvements help the lens collect much more light. The T-stop results are far better for this new version. From 24 to 85mm, the results are good (f/4.3); from 85 to 120mm, the T-stop climbs to f/4.3 to f/4.6 on a D3x. This is far better than for the old zoom on the same camera, which was in any event limited by its smaller aperture at longer focal lengths.

24-120mm f/4 (orange) vs 24-120mm f/3.5-5.6 on an APS-C sensor (D300s)

Increased centre resolution…

The other feature that has been improved is the resolution, especially in the center throughout the zoom range. Reading the summary does not really show a tremendous gain: jumping from 58 lp/mm to 59 lp/mm when used on a D3X doesn’t sound so impressive. But a quick look at the graphs shows that things have changed a lot.
The old zoom was much more limited. Between 24mm and 50mm, you had to stay between f/5.6 and f/11 in order to reach the sharpest resolution. Above 50mm, you had to stop down to f/8 and even to f/11 to stay as sharp as possible.

Center resolution map of the 24-120mm f/3.5-5.6 on a D3x

The new 24-120mm, however, has a very good center definition at any focal length between full aperture (f/4) and f/11, except between 85mm and 120mm, where you have to shoot at close to f/5.6 to remain perfect. Overall, the new zoom is much more comfortable for daily use.

Center resolution map of the 24-120mm f/4: easily above 60 lp/mm on a D3x!

… But not very good in the corners

Center resolution is now very comfortable, and remains so for 1/3 of the field. But as soon as you reach 2/3 of the field, it decreases. To remain above 50lp/mm (on a D3X) you have to stick to 24mm f/8, and between 50mm and 85mm you must use apertures between f/8 and f/11. Fully opened, the lens falls under 50 lp/mm, and plunges under 40 at 75mm. In the corners, the situation is roughly the same.
So, in short, if you want your pictures to have as much definition as possible on their whole surface, the best focal length provided by this 24-120mm is between 50 and 85mm, at apertures within f/8 and f/11.

2/3 field resolution map of the 24-120mm f/4: the graph clearly shows the optimal area: 50–85mm at f/8–f/11.

Vignetting at wide apertures

With respect to vignetting, when used on a full frame sensor, the new zoom suffers from a deeper loss of luminosity than its predecessor. The general vignetting score displays minus 1.9 EV for the new 24-120mm versus minus 1.4 for the old version.
If we look at this phenomenon in detail, we notice a pronounced loss of 2 EV at any focal length between f/4 and f/5.6, except at 24 and 28mm, where the loss is present until f/8, and at 85mm where it peaks again at approximately f/6.3.
This all said, between 35mm and 75mm, the lens is almost perfect at wide apertures (between f/4.5 and f/5.6).

24-120mm f/4 vignetting on a Full Frame sensor (D3x): Except between 35 and 75mm, strong vignetting is noticed under f/5.6, and sometimes at f/8.
24-120mm f/3.5-5.6 vignetting on a Full Frame sensor (D3x): the old version of the zoom suffered from significant vignetting only at the beginning and at the end of the zoom range, mostly at wider apertures.

When used with an APS-C sensor, however, the new 24-120 mm shows almost no signs of vignetting throughout the zoom range at any aperture.

24-120mm f/4 vignetting on an APS-C sensor (D300s): “full green”… meaning that everything is perfect!

Lateral chromatic aberration

Better construction enables the new zoom to perform a little bit better than the previous model when dealing with chromatic aberration. But there are still some perturbations, especially between 24 and 35mm at apertures ranging from f/4 to f/11. For the remaining zoom range, the aberrations are still noticeable between 35mm f/8 and 75mm f/5.6. The best performance of the 24-120mm f/4 is obtained between 50 to 120mm when stopping down above f/8.

24-120mm f/4 on a full frame sensor (D3x): lateral chromatic aberrations are stronger at wide aperture and short focal lengths.
24-120mm f/3.5-5.6 on a full frame sensor (D3x): lateral chromatic aberrations are significant at the beginning and at the end of the zoom range, at any aperture.

Used on APS-C sensors, the scenario changes completely once again: the chromatic aberrations are noticeable along the whole zoom range between f/4 and f/5.6. Above f/8, the lens behaves quite well.

24-120mm f/4 on an APS-C sensor (D300s): lateral chromatic aberrations are essentially contained above f/8.

Distortion: the two generations are very alike

The two generations of the 24-120mm have a very close distortion values, but the old one isa little bit better. At 24mm, the 24-120mm f/4 shows signs of barrel distortion (by approximately 1%). Distortion then disappears around 30mm. From 35mm up to the end of the zoom range, distortion is characterized by pincushion verging towards minus 1%.
Used on an APS-C sensor, the phenomenon is once again less visible. If the graph has the same shape, it is contained between +05% and –0.3% on most of the zoom range. This time the distortion disappears at 35mm and remains almost stable from 50mm (oscillating around –0.3%).

24-120mm f/4 (orange) vs 24-120mm f/3.5-5.6 on a full frame sensor (D3x): the new zoom has a little bit more barrel distortion at short focal lengths, and a bit more pincushion distortion above 50mm.
24-120mm f/4 (orange) vs 24-120mm f/3.5-5.6 on an APS-C sensor (D300s): the two lenses behave almost identically.

So… who is this lens good for?

The new version of the 24-120mm Nikkor zoom is certainly better than the previous one. Its constant aperture as well as its interesting focal length makes it a very convenient “everyday lens,” suitable for travel and landscape and even for sports photography (the last was not recommended for the old version).

This said, the behavior of the lens is slightly different depending on the sensor it is coupled with. It will certainly be easier to use on a APS-C body where most of the problems are handled well, especially with respect to vignetting. But an inferior definition on APS-C sensors makes it a less felicitous choice for demanding uses such as sports, for instance.

On a full-frame body, the 24-120mm f/4 can also perform very well. But the photographer will have to stay within an optimal zone, stopping down the lens at f/5.6-8 (depending on the focal length) especially at the shortest focal length, to avoid too much vignetting and too many chromatic aberrations.

Given its price and specs, this lens belongs to the high-end category. As such, one would expect better performance, especially when mounted on full-frame sensors. Indeed, it is a shame that one has to use this lens at 5.6 to keep chromatic aberrations and vignetting low.