Lenses: Primes vs. Zooms
As someone who has used both types of lenses extensively over the years, I will offer my views both for and against both types.
Let me preface by saying that I made a conscious choice to use prime lenses only; but before explaining why, this article will examine the strengths and weaknesses of both lens types.
Photography is all about trade-offs, and it is no different with lenses.
A prime lens, otherwise known as a fixed focal lens, is a lens which has only one focal length.
Advantages of Prime Lenses
Because a prime lens is optically designed for a specific focal length, it is therefore specialised. It does one thing, and it does that one thing well.
With a prime lens, it can be the case that the optical formula is simpler, and therefore the types of adverse optical effects the optical design needs to counter, are reduced in both number and nature. The use of less lens elements or groups of lens elements contributes to this ability.
Prime lenses are generally (but not always) sharper than their zoom lens counterparts at equivalent focal lengths. Depending on the lenses compared, the sharpness difference can be substantial, or barely noticeable.
Newer lenses may introduce optical designs and lens coating processes which are superior to those of older lenses.
On the other hand, some quite old lenses are legendary for their sharpness despite substantial development as digital photography has become widespread.
Prime lenses tend to be available in wider apertures than zoom lenses, with f/2.8 commonly being the widest aperture in which zoom lenses have been available. In recent years, zoom lenses have become available with maximum apertures of f/2 and even f/1.8. Sigma in particular has been at the forefront of lens innovation and breaking of traditional boundaries.
In the Canon EOS/EF product lineup, the lens with the widest aperture ever released was the Canon EF 50mm f/1.0L USM, which has long been discontinued, and which is somewhat rare and expensive, earning it a position as a 'cult' lens. Currently, the widest aperture Canon offers is f/1.2, in both a 50mm lens and an 85mm lens.
Incidentally, despite its cult status, the Canon EF 50mm f/1.0L USM is notoriously soft at f/1, and produces a strange rainbow effect in the bokeh in some situations. This lens is more desirable for its specifications than its abilities.
In the 1960s, Canon offered an S-mount 50mm f/0.95 lens.
Generally speaking, lenses with very wide or very long focal lengths tend to be somewhat limited in the widest apertures in which they are available. This limitation is due to physics, in that it requires a lot of glass — particularly with long focal lengths — to produce a lens with a wide aperture. This increases the optical complexity, production cost, size and weight, all of which are inherently negative attributes from both the manufacturer's perspective as well as the end user's perspective.
The first benefit is low light ability. Lenses with wider apertures can more easily capture images in low light. This means that a faster shutter speed and/or lower ISO sensitivity rating can be used, which has the benefit of hand-holdability and a cleaner image.
The ability to use a faster shutter speed is particularly important when capturing movement — specifically when there is the desire to freeze subject movement. It is difficult to achieve this objective by using lenses with narrower apertures. There are ways around this, but there are invariably trade-offs. Increasing the ISO sensitivity rating increases noise, and using artificial lighting is not always practical or even possible.
The second benefit is bokeh, the Japanese word for the quality of the out-of-focus highlights.
A lens with a wider aperture means that it is possible to achieve a narrower depth of field, which obfuscates the background with pleasing blur, and isolates the subject from the background. Both effects are visually appealing, particularly for portraiture.
Depth of field is, of course, affected by not only the aperture, but the focal length and the distance between the camera and the subject. The extent to which the background is blurred is also affected by the distance between the subject and the background.
The third benefit of lenses with wider apertures is the ability to autofocus in low light. Modern lenses with electronic apertures leave the diaphragm wide open when composing and focusing, and then close it down to the user- or camera-specified f/stop when exposing.
While this can be the case, it is not always the case.
The Canon EF 35mm f/1.4L USM lens is physically large and heavy relative to its focal length. It is physically longer than the Canon EF 85mm f/1.2L II USM lens, which itself is a monster of a lens, weighing over 1kg.
So, those are the advantages of prime lenses; but what are the disadvantages?
Disadvantages of Prime Lenses
For all the positive benefits prime lenses provide, they also come with some negative attributes.
This is particularly true with longer lenses, such as those offering the 200mm or 300mm focal lengths. Prime lenses in these focal lengths — even those not offering the widest apertures available in those focal lengths — can be larger and heavier than some zoom lenses which cover those focal lengths, albeit at narrower apertures.
A photographer who makes use of prime lenses may find that the size and weight increases, and this must be considered when travelling, as it does not take much effort to consume a lot of space or exceed airline cabin baggage weight restrictions. Having carried large and heavy prime lenses to far away destinations, I am all too familiar with these challenges.
Some zoom lenses cover a broad range of focal lengths, and to cover a number of those focal lengths with prime lenses can mean not only an increase in the number of lenses one needs, but a higher cost, depending on the specifications of the lenses.
One general-purpose zoom lens can easily cover four, five or even six common focal lengths for which prime lenses are available, in a single package which costs and weighs less than a bag full of prime lenses.
By far the most significant disadvantage of prime lenses is the lack of flexibility to change the framing. With a prime lens, the only way to change the view of a subject is to move — or change lenses. In some cases, this is not particularly problematic; but in other cases, there may be circumstances which limit or eliminate the ability to move.
Someone photographing action, such as wildlife, sports or performances, may not have the time to switch lenses. These subjects are very time-dependent, and a moment missed can never be re-visited.
It may not be possible to move positions to change the view. When photographing any of those above-mentioned subjects, you may be limited to the very position in which you happen to be, as it is not safe, practical or permissible to move closer to the subject, or further from the subject. To that end, prime lenses can be quite limiting.
A zoom lens, otherwise known as a variable focal lens, is a lens which offers a range of focal lengths, which can be changed by rotating a ring on the lens barrel.
Advantages of Zoom Lenses
The most significant is the ability to change focal lengths without moving, or changing lenses. As discussed in the preceding section on prime lenses, sometimes timing may be critical, or the shooting position may be fixed.
In addition to the often highly desired ability to change focal lengths easily, is the reduction in size and weight.
One zoom lens can easily cater for the focal lengths of five or six prime lenses. This means that the size, weight, cost and quantity of lenses is significantly reduced. In some situations, this can be essential, as well as desirable.
This can be advantageous for someone on a budget, or with limited ability or desire to carry a bag full of lenses. Convenience is the result.
One other feature zoom lenses offer is the ability to introduce motion blur by zooming during exposure. Admittedly, in my opinion, it is a gimmicky effect which has limited practical application; but occasionally, if done sparingly and with a suitable subject, the motion blur caused by zooming in or out during exposure can result in an interesting image, which no prime lens can capture.
Some people do not wish to change lenses, which in my own opinion defeats the purpose of investing in a camera system designed for the ability to change lenses; but in some situations, changing lenses is not practical or sensible.
So, what are the disadvantages of zoom lenses?
Disadvantages of Zoom Lenses
Naturally, zoom lenses come with disadvantages, too. Remember, photography is all about trade-offs.
Image quality — particularly sharpness — is one of the attributes often cited as a disadvantage of zoom lenses.
One must be cautious when making claims about the sharpness of images captured with zoom lenses — specifically, less sharpness — as it is not quite so simple.
As described earlier, some zoom lenses can rival or exceed the sharpness provided by zoom lenses at identical focal lengths. Modern zoom lenses have come a long way, and the current generation of professional-grade zoom lenses offers image sharpness which would satisfy all but the most fussy, pixel-peeping photographer.
Of course, not all zoom lenses offer outstanding image quality.
The widest focal lengths tend to experience more pronounced barrel distortion; and conversely, at the longest focal lengths, pincushion distortion is not uncommon.
The broader the range of focal lengths a zoom lens offers, the more challenging it is to avoid adverse optical effects.
This is why professional-grade zoom lenses offer a narrower range of focal lengths than entry-level or mid-range zoom lenses. Professional-grade zoom lenses typically do not exceed a zoom ratio of 3x. Entry-level 'super-zoom' lenses can offer zoom ratios in double-digit territory.
The zoom ratio of a lens is calculated by dividing the longest focal length by the widest focal length.
A 24-70mm lens has a zoom ratio of 2.92 (ie, 70 divided by 24 equals 2.92 with rounding).
An 18-200mm lens has a zoom ratio of 11.1 (ie, 200 divided by 18 equals 11.1).
Until relatively recently, whether the aperture was constant or variable, zoom lenses did not offer a maximum aperture wider than f/2.8, and zoom lenses which could open to f/2.8 were typically professional-grade lenses, which cost a lot more than consumer-grade lenses offering similar focal lengths.
As discussed earlier, some lens manufacturers — notably Sigma — have recently offered zoom lenses with maximum apertures wider than f/2.8. Major camera and lens manufacturers such as Canon and Nikon, at the time of writing, have still not yet offered a zoom lens with a maximum aperture wider than f/2.8. Perhaps the third-party vendors, or even other major players, will challenge that and result in wider-aperture zooms becoming available.
Other than professional-grade zoom lenses, mid-range and entry-level zooms typically have variable apertures (eg, f/4-5.6). This means that as the focal length increases, the maximum aperture decreases. The main problem with this design is that if one is shooting at the widest aperture, and zooms in to a longer focal length, the exposure will need to be adjusted, as the aperture will automatically stop down as the focal length is increased.
With zoom lenses offering narrower apertures than prime lenses of an identical focal length, the ability to isolate the subject from the background is reduced. It should be remembered, as discussed earlier, that depth of field is affected by more than aperture; but all else being equal, a narrower aperture results in a less blurred background. Depending on the focal length, camera-to-subject distance, subject-to-background distance and aperture difference, the resulting background blur and subject isolation may not be substantially different.
My Choice of Lenses and Preference for Prime Lenses
As mentioned briefly in the introduction, I shoot with prime lenses only. I have owned a number of zoom lenses over the years, up to the year 2017, when I offloaded my remaining zoom lens, which a prime lens replaced.
I have had zooms and primes for a long time. When I bought my first SLR, I had a pair of cheap, slow kit zooms. When I bought my first DSLR, I also had a kit zoom, and I bought a number of zooms over the years since.
I also bought and sold a number of prime lenses.
What I observed, and what my focal length usage per lens statistics confirm, is that the 16mm focal length was by far my most used focal length on that lens. I used the lens like it was a prime, and I recall being on one shoot, disliking the composition, and then moving the tripod forward to re-compose. It did not even occur to me to simply rotate the zoom ring!
In early 2017, as much as I liked my Canon EF 16-35mm f/2.8L II USM, I decided that I wanted a wider focal length, and I wanted to move to a prime for my ultra-wide lens, so I replaced this lens with a Canon EF 14mm f/2.8L II USM. More details about this lens change can be read here.
A few months later, I decided to replace my long-serving Canon EF 70-200mm f/2.8L IS USM with a Canon EF 200mm f/2L IS USM. Like my 16-35/2.8L II, my 70-200/2.8L IS had brought me many pleasing images, and had travelled abroad on several occasions; but again, I wanted to move to a prime-only configuration, and gain an extra stop in the form of the lust-worthy 200/2L IS. More details about this lens change can be read here.
Even more recently in 2018, with the addition of a Canon EF 24mm f/1.4L II USM lens (story here) which bridged the significant gap between my 16mm and 35mm lenses, I have covered all focal lengths I want, in prime lenses only.
Why did I do this?
I also like lenses with wide apertures, and primes give me that.
I like the look the use of a wide aperture provides, and I like the ability for low light to be of little or no challenge.
All of my lenses have the widest currently available apertures offered by Canon in those focal lengths.
My photography is mostly planned. I do not carry an SLR rig as a matter of course; I go out specifically to shoot, and I take the lenses I know from years of experience that I will need.
The use of prime lenses suits my planned, controlled and specific photography.
It just works for me, and I am very accustomed to it.
Sure, I sometimes end up with a heavier bag than other photographers may like, but for the images I seek, and the capability I want, I can work with this.
With my current array of primes and telephoto extenders, I now have 14mm at f/2.8, 24mm at f/1.4, 35mm at f/1.4, 85mm at f/1.2, 135mm at f/2, 189mm at f/2.8, 200mm at f/2, 270mm at f/4, 280mm at f/2.8, 300mm at f/2.8, 400mm at f/2.8, 420mm at f/4, 560mm at f/4, 600mm at f/5.6 and 800mm at f/5.6.
I cannot complain!
Both types of lenses have their place.
Some people choose to use zoom lenses only, as they like the flexibility and convenience.
Some people — many, from what I have seen — like to use both, and therefore have the best of both worlds, with more flexibility being the key benefit.
It is all a matter of choice, based on the individual photographer's needs and wants.
Hopefully this article has provided plenty of information about both lens types which will help people decide whether one type of lens, or both, is the most suitable choice for the job.
Published on Friday, 26th January, 2018.