Zoom vs. Fixed Focal Length (Prime) Lenses - Which to Choose?

Dec 23, 2008
Bryan Carnathan

Bryan Carnathan

A question most lens buyers face - Should I buy a zoom lens or one or more fixed focal length (prime) lenses?

Camera manufacturers make both for a reason - and there are good reasons for both. I own and regularly use both (but use the zooms much more).

This article contains many generalizations regarding the differences between Canon's zoom and fixed focal length lenses. There are often specific examples that disprove certain generalizations, so be sure to read the specific Lens Review for the lens(es) you are considering.

My generalizations should also be taken comparatively within Canon's lens series. Canon L Series zoom and fixed focal length lenses should be compared with each other, and Canon's consumer series zoom and fixed focal length lenses should be compared with each other.

I should also note that some of Canon's consumer fixed focal length lenses can equal or better some of Canon's L Series zoom lenses for sharpness at some settings. Sharpness is not everything, but it makes a big difference in image quality. Again, check the specific reviews before making your decision.

The major advantage a zoom lens has is its versatility. A photographer using a zoom lens can quickly and properly frame and capture a fleeting opportunity. They can also capture many different framings of the same subject within seconds. The fixed focal length lens user may still be sneaker-zooming to the right distance when the subject disappears - or is no longer in that cute pose. A subject with a rapidly changing distance also favors a zoom lens.

The fixed focal length lens user may alternatively shoot with the framing they are given. This results in a degraded picture - The photographer is forced to crop the picture in postprocessing or leave potentially important details outside of the frame.

Zoom lenses require fewer sensor-dust-collecting lens changes - and fewer lenses to carry. Lens changes are inconvenient and take time - and allow dust to get to the sensor. On the other hand, some zoom lenses move air in/out and can be a source of dust themselves.

In recent years, the general public has heavily embraced zoom lenses. This is reflected in the new lenses Canon has introduced. Since 1999 (when Canon refreshed its Super Telephoto lens line), zoom lenses have been introduced about 4 or 5x as frequently as fixed focal length lenses.

Pictured above from left to right are three lenses from the Canon L Series - the Canon 24-70mm f/2.8 L USM Lens, the Canon 70-200mm f/4 L USM Lens and the Canon EF 70-200mm f/2.8 L IS USM Lens.

Canon fixed focal length lenses are usually faster (have a wider aperture) than their zoom counterparts. To me personally, this is the greatest value of a fixed focal length lens.

A fast fixed focal length lens allows action-stopping shutter speeds to be used in low-light situations. Fixed focal length lenses are sometimes the only solution for dark indoor sports photography. I should mention that the ever-improving high ISO performance of new DSLRs is making fixed focal length lenses less important in these situations.

A fast lens also allows excellent subject isolation by blurring the distracting background. The results can be beautiful. Conversely, an extremely wide aperture creates a razor-thin depth of field - this is not adequate in many situations.

Canon fixed focal length lenses are smaller than their zoom equivalents. Canon non-L fixed focal length lenses are generally much smaller than Canon L-zooms in the similar focal length range.

Canon fixed focal length lenses are usually sharper than their zoom counterparts - much sharper in the non-L lenses. This difference is much less noticeable in the Canon's L Lens Series, although some non-L fixed focal length lenses can best L-zooms slightly at comparable apertures in this regard. Fewer lens elements contributes to this attribute - as well as a reduced tendancy for contrast-robbing flare.

A very rough generalization: Canon fixed focal length lenses are usually less expensive than their zoom counterparts - if they have comparable wide apertures. When the fixed focal length lens apertures start getting much wider than the comparable zoom's aperture, prices may actually cross over. Canon's non-L fixed focal length lenses are always much cheaper than Canon's L fixed focal length lenses and zooms.

Any cost savings can evaporate when multiple fixed focal length lenses are required to cover the focal length range of one zoom. Having backup lenses available is a nice side effect of multiple fixed focal length lenses.

Some focal lengths are only available from Canon in a fixed focal length lens - such as the Canon EF 500mm f/4L IS USM Lens or the Canon EF 14mm f/2.8 L. Some lens types are not offered in a zoom - Canon does not offer a true 1:1 Macro zoom lens.

I have heard photographers talk about using strictly one fixed focal length lens to spawn creativity. I don't agree with that reasoning as you can just as easily spend a day with your zoom lens set to a single focal length. Then spend the next day at a different one. *If* the basic premise helps you. Of course, when the shot-of-a-lifetime happens upon you, you can break your promise to yourself and zoom to the proper focal length to capture it! Some also say that all images start looking the same when shot with a single prime lens.

Some photographers only need one focal length for most of their work. If this is the case for you, a fixed focal length lens likely makes the most sense. Pick the one that is best for you.

My personal preference is for canon's L-zooms. I will usually pick up an L zoom in the 16-200mm range over my fixed focal length lenses UNLESS I need a higher shutter speed than my zooms' apertures can give me (for shooting a moving subject in low light) or I need the extra background blur one of the fixed focal length lenses will provide. The optical performance of Canon's L zoom lenses is outstanding - they get the job done best for me the most of the time.

There are valid reasons for owning either or both - You ultimately must decide what is best for you.

I hope this article has helped you compare both zoom and fixed focal length lenses. Again, read my individual Canon lens reviews to find out which lens is best for you in the focal length you need.

Bryan Carnathan's passion for photography began at the age of 15, when he was working any job he could find to save for his first SLR. His passion for technology resulted in his pursuit of a degree in computer science, and his subsequent work in the business world related to information services consulting and directing. Carnathan launched The-Digital-Picture.com in November 2003, with an initial purpose to sell stock photos online. Yet his audience was interested in the equipment he used for his images so, after spending time answering gear-related questions on some online forums, he changed the direction of his site to concentrate on equipment selection intermixed with teaching. His present site is a blend of his love for helping people, his love of technology and the Internet, and the passion for photography he has had since childhood.

The latest addition to the PDN family, the PDN Gear Guide in print, has a total circulation of 30,000, and covers the latest and greatest in photographic equipment. Initially created in 2006 to be the official guide to PDN's annual flagship photography event, PDN PhotoPlus International Conference + Expo, the PDN Gear Guide is now also available online for gear news and updates 365 days a year.
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