Canon’s 8-15mm f4L fisheye is an unusual lens, the only fisheye zoom that I know of. Most fisheye lenses are primes.
Following on from my article A Concise Guide to Choosing a New Lens I thought it would be interesting to go a little deeper into the question of whether to buy a prime lens or a zoom.
First, the definitions:
Prime lenses have a fixed focal length. There is no zoom ring and no way to magnify the subject other than moving closer. There are two settings to adjust: aperture (often handled by the camera) and focusing distance.
Zoom lenses have a variable focal length. There are three settings to adjust: aperture, focusing distance and focal length.
Both primes and zooms have benefits. I’m not going to try and persuade you one way or the other. Rather, the goal is to explore the benefits of both to help you decide which is the best for you.
Benefits of prime lenses
Image quality
Generally speaking, prime lenses have better image quality. It is easier to make a lens with good optical performance at a single focal length than it is to make one that performs well through the entire range of a zoom lens. This is especially true with wide-angle lenses where zooms tend to suffer from barrel distortion at the shortest focal lengths. With longer focal lengths (ie. 50mm plus), there is less difference in the performance between zooms and primes.
This photo shows the barrel distortion of an 18-135mm zoom lens set to 18mm. The curved lines in the frame should be straight.
Size and weight
Prime lenses tend to be smaller and lighter than zooms covering the same focal length range. This isn’t true all the time, high end primes are bigger because they have wider maximum apertures, which need larger lens elements to let the light in. Anyone who has used Canon’s 85mm f/1.2L prime lens knows what I mean – it’s a monster.
Don’t forget that the size and weight advantage is quickly lost if you end up buying two or more primes to cover the same focal range as a zoom. But if your aim is to use your camera with a single, lightweight lens then primes are the way to go.
An advantage of smaller lenses is that they are less obtrusive for portrait and street photography. It’s interesting how lens size affects the dynamics of a portrait shoot. In my experience models, even experienced ones, are much more relaxed in front of the camera when I use a smaller lens.
The Canon 40mm f/2.8 pancake lens is about as small and light as you can get. Pancake lenses are the ultimate in unobtrusive lenses.
Wide maximum apertures
The wider maximum apertures of prime lenses are useful for taking photos in low light or for creating beautiful bokeh. They also let more light into the lens, giving you a brighter image on cameras with optical viewfinders. However, if you have a camera with good high ISO performance you may not be so bothered about the advantages of using primes in low light.
You can only take portraits like this one that have very little depth of field with prime lenses. Shot at f/1.8 with an 85mm lens.
Value for money
Prime lenses often give really good value for money, especially at the lower end of the price range. Most manufacturers have inexpensive prime lenses in their range that give superb image quality, much better than you would get from a zoom lens costing the same.
Benefits of zoom lenses
There was a time when the quality of zoom lenses was so poor that most photographers didn’t use them. Thankfully, things have changed and they have become more popular as the quality has improved. These are the main benefits of zoom lenses:
Convenience
The main benefit of zooms is the convenience arising from covering a range of focal lengths in one lens. This can save you time (swapping lenses) and money (being cheaper to buy one zoom than two or more primes). Zooms are useful as walkabout lenses, or if you are working in dusty or damp conditions where you don’t really want to take the lens off the camera.
With so many benefits, are there any disadvantages? Unfortunately the answer is yes. Here are some things to bear in mind:
The trade-offs for convenience are image quality and size. Zooms tend to be bigger than primes, and if you want one that has good image quality throughout the entire focal length range then you will need to spend some money. One tip is to go for lenses that cover a shorter focal length range, such as a 24-70mm rather than 18-200mm.
A kit lens with variable maximum aperture. Avoid these types of zooms if you can.
Another thing to watch out for on cheaper zoom lenses is variable aperture. An example: an 18-55mm f/3.5-5.6 kit lens has a maximum aperture of f/3.5 at the 18mm end but only f/5.6 at 55mm. This makes it harder to work in manual mode (what if you have the aperture set to f/4 at 18mm and then zoom in to 55mm?) and is a general hassle all-round. Pay a bit more and get a fixed aperture zoom.
Saves you having to move
While some people will tell you that a benefit of prime lenses is that they make you zoom with your feet (ie. move closer to or further from the subject to change the composition) there are times when this isn’t possible. You may be at a sporting event, and unable to get any closer to the athletes involved. Or you may be standing near the edge of a cliff taking a landscape photo, unable to move further forward because you would fall off. Zoom lenses are invaluable in situations such as these.
I took this photo standing near the edge of a cliff. I couldn’t move any further forwards, but was able to frame the image precisely using a 17-40mm zoom lens.
Your view
Now it’s your turn. What lenses do you prefer to use – zooms or primes? Have you bought any lenses recently and why did you decide to buy them? I’m looking forward to reading what you have to say.
Understanding Lenses ebooks
My ebooks Understanding Lenses Part I and Understanding Lenses Part II will help Canon EOS owners decide what lenses to buy for their cameras. They are both filled with lots of tips to getting the most out of your Canon lenses. Click the links to learn more.
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