Primes or Zooms?

 

Nikon Z 50mm f/1.8

The question in the title is a frequent topic in every discussion, all forums, and many videos on photography. Some say it is an out-dated problem pointing to the quality that zooms have reached by now. First there were only prime lenses, zooms being a much later invention. It is therefore no surprise that zooms for a long time were not on par with the much more developed primes. But now, we can optimize lenses on computers and use more modern techniques in fabrication. Zooms have reached very high standards. 

This is a longer text. So it is a good idea to put my main conclusions up front.

• Zoom lenses are for flexibility, lightness and compactness. They are meant to be used when you do not know what to expect, or know that you will have to cope with different kind of scenes. 
• Modern zoom lenses can cope with prime lenses at f/8, and often already at f/5.6. 
• Prime lenses are special lenses and should be used as intended, i.e., wider open. This will isolate your subjects and also help in low light to avoid high ISO or yield a faster shutter speed.
• Another reason to use a prime lens is consistency and speed. Some photographers see the world like their prime does. This eliminates choices and helps to develop a consistent style.

The main problem of zooms is that they have to compromise along the focal range they serve. A 24-200 can impossibly be excellent at 24mm and at 200mm as well. Usually, they are made to work well enough from the short to the long end with some excellence at a particular focal length. But a good prime can beat it even at that focal length. And there it will beat it in almost all areas, such as sharpness, distortion, chromatic aberration, chroma, flare resistance, contrast, prize, size and weight. E.g., the most excellent Nikon Z zoom is the admirable 24-70 f/2.8. One must admit that it beats many of the cheaper primes, but the 50mm or 85mm f/1.8 still are better at their focal length at one third of the price, and in a much more compact format. 

For the amateur or casual shooter, a top lens like the Nikon Z 24-70 f/2.8 is out of question anyway. It is well above 2000€ and a beast to carry around. For travel and street, we all want a compact set which is affordable to replace when it gets damaged or stolen. The question arises weather it is better to take a prime lens or be satisfied with one of the more mediocre zooms.

Nikon Z 35mm f/1.8

In the Nikon Z lineup for full frame cameras, we find the Nikon Z 24-70 f/4, and for the DX line there is the equivalent Nikon Z DX 16-50 f/2.8. Those are reasonable choices because they compare in size, weight and price to prime lenses in their range. They are "kit zooms" bundled with the camera, and you often get them used a lot cheaper. The recent 24-120 f/4 or the 24-200 f/3.5-6.3 VR are similar options.

But how do these lenses compare in practice? There is one truth that you cannot deny:

Modern lenses are almost identical at f/8.

I have shot enough with the Nikon Z 24-70 f/4 now to tell you that you will have a hard time to distinguish the results to one of the excellent primes, even at f/5.6 which is its sweet spot. Closed down, other aspects of lens quality are much more important. One is flare resistance. It is achieved by the coating on the lens elements. That helps to reduce loss of contrast in difficult lighting. All Nikon Z S-line lenses have such a good coating, and the 24-70 f/4 is one of them.

Nikon Z 24-70 f/4

Other aspects of lens quality are the absence of chromatic aberrations. It can be fixed in post to some extent, but in difficult situations, such as branches against a bright sky, it can spoil the image, especially when lens flare adds to the problem. Distortion can also be fixed in post, but the fix might deteriorate the corners. Another aspect is the cooperation of the lens with the autofocus system of the camera. One has to admit that in all these areas, primes are better. But at f/5.6 and above, the differences are very small.

We must also  discuss image stabilization. Of course, it only helps for scenes without object movement. For sports and kids running around, it is more ore less useless. Nevertheless, it is such a helpful feature that I consider myself severely restricted without it. The alternatives, a tripod or high ISO, are usually not available for the kind of photography I do. For videographers, image stabilization is necessary to achieve a professional look and results that are a joy to look at. The problem is that cameras without IBIS can often not provide any image stabilization on primes, but have zoom lenses with VR.

As a summary, we see that a modern zoom can often yield satisfying results with much more flexibility than single prime lens. But there are more arguments to use primes.

Primes are to be used wide open.

That's their intended purpose. It is easier to make a high level f/4 lens than a lens with f/1.8 or f/1.2. Nikon has the small and cheap 28mm f/2.8 and 40mm f/2 lenses which are already very good if you use then at f/4 and above, almost reaching the level of the f/1.8 S-line. But they do not offer the same quality at f/2.8 or f/2. And the f/4 zooms do not even reach that speed.

Besides the normal line of f/1.8 primes, Nikon has high end primes like the 135mm f1.8, or the f/1.2 lenses. Those are very expensive and also not at all compact. What are we to achieve with these lenses? Is it only even more sharpness at f/5.6?

Nikon Z 85mm f/1.

The wide open look is all about object isolation. It generates the one effect that we associate with photography, leading the eye automatically to the sharpest area of the frame. Isolation of a subject can be achieved with other means too, such as contrast, color or light, or even composition. Painters used such tools for centuries. Blurriness is the photographic mean that we have at our disposal.

This is not to say that a photograph with sharpness everywhere is bad. It is just something different. If you are into that kind kind of shooting, go ahead. The skills needed are more to generate layers, use composition, and catch the right moment. That might be even more difficult than to go out with a 85mm f/1.8 lens which shows everything beautifully that you throw at it.

There are different genres of photography.

Wide open, the Nikon Z lenses are made to be sharp in the center, usually reaching a peak sharpness at f/2.8. At that point, the sharpness outside the center is already on a sufficient level, although a lot below the crispiness at the center. To optimize the fast primes in the center makes a lot of sense because they are not meant to achieve a big depth of field.

It would be wrong to ask for much sharpness in the corners wide open, especially not for wide angle lenses. A 15mm lens might deliver sharpness across the scene even at f/5.6. You can also use a 35mm wide open to isolate subjects. But then, you will have to get close to your subject and do really not need a super sharpness in the corner.

Nikon Z 14-30mm f/4 @f5.6

To isolate a subject, a longer lens is better than a wider lens. Although the depth of field will be almost the same at the same aperture when the subject fills the frame at each focal length, the background will look drastically different. It will be softer and there will be less disturbing elements. That is one reason why telephoto lenses are used for portraits. The other reason is the lack of distortion of nearer elements like the nose of a subject. 

There are other arguments pro prime lenses. Photographers who shoot with a specific prime only, often say that they start to see the world like their prime. They instantly know how the picture will look like when they see the scene. It is easier for a human to restrict to a single tool and learn it by heart, than to maneuver through complex options. And it is faster.

Another good argument is consistency of your output. Even between 24mm and 70mm there is a big variety due to the focal length alone. If you mix wide angle with telephoto in a documentation, an outstanding style might be impossible to achieve. For the casual shooter, this argument is probably void.

You might select a prime for consistency and simplicity.

In summary, every lens is made for a specific purpose. Even the zooms are made for flexibility and ease of use. The best use of a lens is following the intended and inherent purpose of this lens. Moreover, if you always just aim for the optimal lens quality, you might be neglecting the importance of all the other factors in photography, like a good eye, technique and good light.

Personally, I do not hesitate to go out with my 24-70 f/4 as the only lens for a walk. Of course, I sometimes want something wider or longer. But each option comes with new compromises and new challenges. E.g., the 24-120 f/4 is heavier and longer, and does not provide the same smooth transitions to the background, due to the more complicated lens design. 

I take a prime lens, usually the 50mm f/18, whenever I am sure to use it in its intended style, like when I visit a museum or also make portraits. If I expect low light, a prime is often the only solution. The 35mm f/1.8 is another option. It is very versatile, but a bid on the boring side. Nevertheless, it is my recommendation for anyone who wants to go prime, but not face too many restrictions.

Nikon Z 35mm f/1.8 @f/2.8