Lens Rentals: That Zoom Lens is Not ‘as Good as a Prime’… Here’s Why

Roger Cicala—the founder of Lens Rentals and one of the most entertaining and informative voices in the world of optical testing—has some news for you: zoom lenses are never as good as primes, and they vary so much from copy to copy that you should probably never trust a zoom lens review.

In an entertaining post packed full of test charts and MTF charts and a few “subliminal” messages of encouragement, Cicala tackles a common statement that annoys him to no end when he sees it online.

This zoom is just as good as a prime.

The reason why this statement is just plain wrong comes down to optical complexity. “A lot of people are aware that while a zoom can be as sharp as a prime in the center of the image, it rarely is in the corners,” writes Cicala. “Few people, though, think about that fact that zooms are far more complex than primes.”

Where a prime might have 6 to 12 lens elements, a high-end zoom frequently doubles that number, adding a ton of variability. So while you can find a great and a crappy copy of a prime lens, the same can’t really be said about a zoom lens—that zoom might be amazing at 200mm and total crap (relatively speaking) at 70mm.

Case in point:

The chart above shows the variability of 8 different 70-200mm zoom lenses tested at 70mm, 135mm, and 200mm. In this case blue = good/sharp, and the amount of variability you see between these 8 lenses is not unusual.

Head over to the Lens Rentals post to dive WAY deeper into this and read Cicala’s full conclusion. And remember, if a reviewer who tested one version of one zoom lens says that lens is “as good as a prime,” don’t believe them.

Image credits: Header image by Carlos Delgado; CC-BY-SA.