Monday, May 19, 2014

Bokeh Shootout: Nikon AF-S 58mm f/1.4G vs 50 mm f/1.4G



The Nikon 58m f/1.4G was an immediately controversial lens when it was released at the end of 2013. Even though it is the dream of every enthusiast photographer, there are fewer opportunities to shoot wide-open at night than in more reasonable lighting conditions during the daytime. Thus, the 58mm lens immediately developed a reputation for under-performing relative to its price tag. That in itself is not new; none of the Nikon f/1.4 primes are truly justifiable if you aren't shooting for a living. However if there is one malady that gear-heads suffer from (just one?) it is that many fall into the trap of thinking that if something is not good for them, then its also not useful for others.... and so, vast quantities of forum chatter are generated based on this logical fallacy.

For examples of what the 58mm as a NOCT lens is good for, have a look at these nighttime shots. Otherwise, read on for what this lens does under daylight conditions. As with all good stories, there's nuance to this one:


(Updated May 2014: Additional bokeh samples by aperture.)

At The Same Focal Distance


Here are back to back JPEG shots with the two primes as shot on a Nikon D800 with the focus subject (terracotta warrior figurine) placed four feet away from the camera focal plane. (Matrix mode, aperture priority, Live view, aimed on the chest armor) Naturally, the 58mm  produces more image magnification, which is beneficial to generating bokeh because the background blur gets magnified relative to the subject.


50mm, 1/80s
58mm, 1/60s
Immediately, some subjective differences are apparent. The 58mm does indeed produce smoother-looking backgrounds, but the 50mm gives the scene more overall contrast. Note the lesser amount of vignetting on the 58mm; this is quite low for a prime shot wide-open. Compared to the 50mm, the light falloff from center to corner is less and also occurs in a smoother manner.

Also note the difference in exposure; the camera picked a shorter shutter speed for the 50mm image to compensate for the inclusion of some of the lights. (Yes, that's a testing goof, but when the equipment is not yours and the camera store is not your personal studio you do what you can with limited time. Otherwise....whoops)

Click below for a 100% crop of the center of the image:

Center
Here's where the asterisks start start popping up. There's a difference between detail and contrast. Generally speaking, the 58mm is not a "sharp" lens when shot wide-open. However, it is still picking up detail that can have contrast added back in during post-processing. Otherwise, because of the difference in exposure (albeit slight), not a lot can be said conclusively about the differences between these two lenses when you look at it at this level of detail. By f/2.8, the situation improves and the overall sharpness of the 58mm is more in line with the other nifty-fifties. If there is a stand-out weakness to the 58mm, it is with longitudinal chromatic aberration, which the in-camera JPEG engine doesn't correct for (unlike lateral CA).  

There is a verifiable difference in bokeh... not just the amount but also the quality. Looking at the back wall where the Leica display is, you can see that the 58mm almost completely obliterates the silver boxes into an even blur. The 50mm does a competent job, but the highlights are a bit more fringed than with the 58mm.

Middle left

At the Same Subject Magnification


The following is a set of images from f/1.4 to f/5.6 with the camera and lenses positioned so that the figurine is (approximately) the same size within the picture frame, which only equates to a change in position of a few inches/centimeters. Exposure is by spot meter on the figurine, with the same exposure used at each aperture.

This set of images is more helpful for evaluating center sharpness than above, as the the exposures are equalized. However, the same trends are present; wide open the 58mm does not give the same visual impression of sharpness as does the 50mm, and you can see the same fringing around the figurine as in the first set of images. However, the center portion of the frame sharpens up quickly by f/2.8, and from here it's arguable that the 58mm is actually a bit more contrasty than the 50mm.

The 58mm does not perform well on most published tests because it has a fair amount of field curvature. What this means is that if you are shooting at a flat test target, when the center is in focus, the corners will be unsharp because the plane of focus curves away in three dimensional space. This is less important in real-world shooting, and especially people and portrait photography.

When comparing bokeh, the 58mm produced smoother looking background bokeh than the 50mm up until f/5.6. There is less highlight fringing throughout the aperture range. In fact, it's remarkable how much blur retention there is despite the lens being stopped down.Click on the images to see the 100% crops at proper size.

 At f/1.4


Nikon 58mm
Nikon 50mm
Center Crop
Far Right Crop

At f/2.0


Nikon 58mm
Nikon 50mm
Center Crop
Far Right Crop

At f/2.8


Nikon 58mm
Nikon 50mm
Center Crop
Far Right Crop

At f/4.0


Nikon 58mm
Nikon 50mm
Center Crop
Far Right Crop

At f/5.6


Nikon 58mm
Nikon 50mm
Center Crop
Far Right Crop



Concluding Thoughts


Nikon 58mm on D800 and 50mm on D610

The 58mm lives up to its billing as a Noct lens, but outside of that application it is also an impressive lens for generating bokeh in daylight conditions. There are two caveats with that: the first is that the price makes this lens economically unfeasible for most DX users. Having this amount of bokeh for a 58mm DX portrait lens sounds like a good idea, but there other other cheaper alternatives like the 50mm f/1.4G or the 85mm f/1.8G. On an FX camera, having this amount of bokeh at the 50-58mm focal length sounds like a street-shooter/documentary photographer's dream, but the subjective appearance of the images doesn't live up to that billing.

Even though the Leica Summilux 50mm isn't a perfect lens, it's a lens that produces gorgeous images; the Nikon 58mm is similar to the  Summilux in this regards. It's got creamy bokeh like the Leica,and so long as you you don't open it up all of the way, it will also generate sharp and contrasty looking centers as well. In fact, with the quality of the bokeh with the lens stopped down, there is less need to shoot the 58mm wide-open, as it is possible to take advantage of it its contrasty center rendion and increased depth of field while retaining the ultra-smooth background rendition. In this regards, it's not quite up to what the Summilux does, as the lack of contrasty and longitudinal chromatic aberrations wide open give the Nikon 58mm images something of a veiled look. However, the AF-S 58mm is like the Leica in that it it is not a perfect lens, but it is a lens that produces a distinctive look.

In other words, if you want this lens and are a little bit unsure about how you will be using it, its imperative to try before buying. Most shoppers simply looking for "the best" would be better served by the Sigma 50mm F1.4 DG HSM Art.  The Nikon 58mm is good at what it does, but as a specialist lens it is the kind of optic that might not produce instant agreement between photographers with differing usage requirements.  The more you shoot with this lens, and the better you know its ins and outs, the more distinctive the images that you can pull out of it. However, if you are looking for extremely good wide-open nighttime shooting, go right ahead... so long as your wallet is willing. 



With thanks to Broadway Camera.

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