If you haven’t noticed, I like to know a lot about things that I work with. I thrive off information. I think it makes me better at my job, and also better at my hobbies, but tends mean that my though processes, and as a result my blog posts, tend to be fairly lengthy. So, after 3 massively long posts, I think I may try to make this one a little more succinct. This week’s topic is another one where point and shoot users will likely only find intellectually interesting as there are not a lot of applications for the usual P/S camera. In fact, it may be tough today to find a standard P/S camera today that has anything but a zoom lens on it. Why? Because you only get the one lens, so you might as well build it with versatility. This week’s topic is again for DSLR users and of course mirrorless interchangeable lens cameras (ILCs). So what is it? Well if you are familiar with cameras already, then the title gives it completely away. But, if you are new to the world, you may not know the terms, what they are, how they are different, and which is better. Today’s post is on zoom lenses and prime lenses and the advantages and disadvantages of both. And before I start, I realized when I started writing this one that it may have been a better post for later on after I go through the different focal lengths of lenses, there is some information here which is relevant to those future posts which is why I did it in this order. Also, while I am trying to do some of this in somewhat of a logical order, I do plan on expanding to some slightly more advanced topics in the future and then I’ll come back to some of the basics, and so on, but for now I’m trying to keep many of the basics up front in case you are reading through these chronologically.
For DSLR and ILC camera users, there are effectively two types of lenses to choose from. This is regardless of what brand, mount, image sensor type, etc, that you have chosen. The two types of lenses are zoom lenses and prime lenses. So what am I talking about? Well, most people are probably familiar with the term “zoom” and likely can figure out what a zoom lens can do. A zoom lens is a lens where the user can adjust the focal length, and as a result, the view of the subject as it relates to a wide or narrow area of that subject is hitting the image sensor. What then is a prime lens? As you might guess, it is the opposite of a zoom lens. It is a lens with a fixed focal length. Well, I realize now that anyone new to the world of DSLRs and understanding lens selection may be wondering what exactly is focal length (I promise we’ll get right back to the two types of lenses, their advantages and disadvantages).
**Mild Tangent Alert**
Focal length is technically the distance of the optical center of the lens to the sensor plane (or film plane) when focused to infinity (farthest focus on your lens). So theoretically for a 100mm lens, the optical center of the lens is 100mm away from the sensor when the lens is focused at infinity. This gets a little more complicated as most lenses today and for well before the existence of SLR cameras, have used a retrofocal design. In a symmetrical optical lens setups, there were be roughly an equal number and symmetrical positioning of lens elements, so as light was collected by the front elements, it would be reproduced on the same scale (angle of diffraction) as it was emitted from the back elements. A retrofocal design uses an asymmetrical setup of the lens elements, where there are more elements of narrowing diameter towards the back of the lens as compared to the front. This allows designers to shift the location of the optical center, even to the point of moving behind the last element, or in front of the front element of the lens (essentially the optical center is in the camera body). Without a retrofocal design, it would not be possible to have a lens with a shorter focal length (wide-angle and even normal) as the lens would have to be mounted essentially only a millimeter or two from the sensor in order to get the optical center close enough and to produce an image circle small enough for the image sensor of the SLR. Mounting a lens this close would get in the way of the workings of the camera. As such, the distance between the sensor and the lens on most SLRs is at least 40-50mm and that does not include the distance to the optical center of the lens, making it impossible to get a lens with a shorter focal length than say 75 or 85mm using a symmetrical design. On the flip side, super-telephoto lenses, would be much longer than they already are. And there’s more to it, but basically know that more symmetrical optical lens designs are not compatible with, and thus not used for, SLRs and point and shoot cameras. It should be noted, that symmetrical lenses can be used on some larger format cameras, but never on an SLR, or point and shoot.
Ok, so enough about this for now. I’ll talk more about focal length in upcoming posts on the different groups of focal lengths for lenses: super wide-angle, wide-angle, normal, short telephoto, telephoto and super telephoto. In short, the larger the focal length, usually in mm, the more magnification power you have for distant object, but also a narrower angle of view (of the total 360 degrees around you head as you have camera up to your eye, you may only be able to see a couple of degrees of that). The opposite is true for shorter focal lengths; less magnification and wider angle of view.
**Mild Tangent Over**
After that brief design less, I’m now back on topic. So you have your camera body, and you want to pick a lens. Should you buy primes or zoom lenses? Giving away the punch line, each of the two types has their advantages and disadvantages.
If you have bought a camera kit, body with a lens, chances are that lens is a relatively inexpensive zoom lens. The reason for this is that the zoom lens gives you more versatility, and if you are just buying your first camera and get a kit, chances are you don’t have any other lenses to use. This is the biggest advantage of a zoom lens. (As an aside it should be noted that a true zoom lens is a parfocal zoom which means as you zoom in and out, the focus of the lens should not change. However, due to the expense of producing this style lens, the majority of zooms today are varifocal in type, meaning that you will lose focus as you zoom in and out. While more inconvenient for the photographer, it really is not a huge deal as you just refocus when you get to the zoom you want.) Zoom lenses by their very nature are more versatile than prime lenses, because you essentially get a range of coal length s to use with the twist of the zoom ring, and without having to change lenses. This means you can quickly adjust from one focal length to another without the time and expense changing between multiple primes, while also eliminating the risk of getting dirt and dust inside the cameras as you swap out lenses. I personally own several zoom lenses and this ease of use is exactly why. As an example, the kit lens that comes with my D90 is an 18-105mm zoom lens. This lens allows me to shoot at 18mm which is decently wide and then quickly zoom in on a subject using the telephoto range of the 105mm length, and hit every focal length in between. Nikon also makes a fantastic 18-200mm zoom which has even more versatility (and overall is a better lens, but at twice the price). There is also a class of “super zooms” which essentially is a zoom lens with a range exceeding 6x. Technically the 18-200mm is a super zoom. Sigma makes a lens that ranges from 50mm (a normal focal length) out to 500mm (a super telephoto focal length) all in one lens. This is a lot of flexibility to have and use with the just the twist of a zoom ring.
You may ask then, if you can get all of these focal lengths in one zoom, why in the world would you own a prime lens? Well, the answer is simple. In general, zoom lenses are inferior to prime lenses in almost every other way (with a few exceptions, such as the Nikon Nikkor 14-24mm zoom which many consider to be the gold standard for wide angle zooms, and surpasses most wide angle prime lenses). Zoom lenses typically have a limit of how wide of an aperture that is available, and many have variable maximum aperture sizes depending on the focal length you are using. For example the high end 70-200mm zoom lenses from Nikon can have a constant maximum aperture of f/2.8 across the range, which is decently wide, but is two stops slower than say a Nikon 85mm f/1.4. Constant aperture for a zoom lenses is also typically only found on the high end, professional zooms lenses which usually start above $1500 and can go up to several thousand. Most lower end zooms that most people have the budget for, have a variable aperture across the zoom range. For example, the kit lenses I mentioned is listed as a Nikkor 18-105mm f/3.5-5.6. This means that at 18mm it has a maximum aperture of f/3.5, but at 105mm it has a maximum aperture of f/5.6. In between it will decrease the maximum aperture from f/3.5 to f/5.6 as the focal length is increased from 18mm to 105mm. Either way, these apertures are much slower than the equivalent primes and the high end zooms.
Zoom lenses are also comparably more expensive than a related prime with similar image quality. Because lenses that cover multiple focal lengths need a more complex design, that often means they are more expensive. The flip side of this is a zoom lens of comparable price to a prime will have a lower image quality. Because the manufacturers are trying to maximize image quality at multiple lengths, often times there is a sacrifice for quality at each specific focal length. The saying here goes, “jack of all trades, master at none.” The complex design can often mean that there is additional chromatic aberration or distortion not seen in an equivalent length primes lens. Again, this is not always true, but it is more often than not. As such a zoom lens with comparable image quality as the related prime at a given focal length (for example, a Sigma 50-500mm set at 400mm is going to be nowhere near a Sigma prime lens of 400mm focal length.
Zoom lenses are also heavier and more complicated because they need to contain more glass elements and moving parts to properly focus the light across a range of focal lengths. The weight of a lens at shorter focal length is not often a huge concern, but when you get into longer lenses, the weight can make the difference between being able to handhold a shot, or not. The more glass and moving parts, in addition to increasing cost and weight of the lens, also means that there are more changes for the lens to malfunction or have a design flaw. Again, this is generally speaking.
The biggest benefit of prime lenses is image quality. The lens is designed from scratch to work at one focal length and therefore more fine tuned to product a sharp, rich image. All of the disadvantages of the zoom lens found above are advantages in primes, but on the opposite end, the prime lens is limited to the one focal length.
It should be noted though that lenses of 400mm and up, often carry a very hefty price tag ranging up to and in many cases, exceeding $10,000. These are finally engineered, professional lenses, and are often only found as primes (although Sigma has made a 200-500mm f/2.8 zoom which works really well, but sells for $35,000).
So which should you choose? Do the disadvantages of a zoom outweigh the versatility benefit? Not necessarily. Zoom lenses are great and for most every day photographer, they produce great images. I think the benefit and flexibility of zooms is a huge advantage, but do you research and read reviews. There are a bunch of great review sites out there and people have opinions on whether or not a lens produces good images. And, don’t let price fool you either. Nikon produced a rather pricey 24-120mm which produced junk pictures, but the $150 18-55mm kit lens that came with my D40 produces great images. That being said, there are places for primes. Aside from the long focal lengths is you are into wildlife photography, I think that every photographer should own a 50mm fast ( f/1.4 or f/1.8) prime lens. Ansel Adams was famously known for only using this one lens for all of his shots, and everyone of them is fantastic. This fast primes will give great photos and you can easily make up for the lack of versatility by moving closer and farther away from the subject. The bottom line is, that there is a place for zoom lenses and prime lenses in your photography bag. Do you research on your lens and buy wisely, and you will be happy.
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