Spend a few minutes perusing the technical corners of the photo internet and you’ll undoubtedly encounter the name Roger Cicala. The LensRentals.com founder has become something of a photo nerd rock star for his exhaustive technical analysis of lenses, his gear tear downs and his general erudition on all things optics (not surprisingly, he was an optometrist before founding the company). We caught up with Cicala to pick his brain about prime lenses. Here’s what we learned.
Great Prime Lenses Are Big Prime Lenses
One of Cicala’s favorite families of prime lenses is the pricey Zeiss Otus models, one of the very few lenses he’s tested that can resolve 250 line pairs (where 50 line pairs is considered high). Cicala says the engineers working on Otus were not constrained by price or, crucially, size. “You can only curve [lens elements] so much,” he says, and the imperative to make lenses small forces more pronounced curvature, which makes incoming light harder to control. “Larger lenses have a gentler curve” and the result is an incredibly sharp, high quality image.
It’s Not Just About Bokeh
Lens makers love to tout the beautiful bokeh produced by their lenses but Cicala says field curvature (i.e. how focus falls off) plays an equally important role in the look of your image. The plane of focus may cut straight across the image but may also curve toward or away from you, which affects not simply what’s in focus but how bokeh is reproduced, Cicala says. Unfortunately, a lens’s field curvature isn’t a spec you can check, like aperture or focusing distance. You’ll just need to shoot it to see how it performs.
Fast Primes Are Hard to Build Well
“The aperture is an integral part of lens design and it’s the place to cut off aberrant light rays that cause problems,” Cicala says. Fast primes (think f/1.4 and wider) let in a lot more light and introduce a lot more optical maladies that need to be corrected for.
More Lens Elements Doesn’t Necessarily Mean Better Quality
Adding more lens elements is the “ultimate double-edged sword” in lens design, Cicala says. On the one hand, more elements help you remove optical aberrations. On the other, the more lens elements you add, the greater the chance that they’ll be misaligned during assembly. “The misalignment of each piece is additive,” creating a cascade of errors as you pack in more glass elements, he says. Lenses with many elements will also show a greater variance between identical copies, Cicala adds.
Why Manufacturer’s MTF Charts Aren’t Always Accurate
“The MTF curve that the lens manufacturers put out tells you how the lens should be when it’s perfect,” Cicala says. But in the real world, imperfection is the rule. “I sometimes find a big deviation between what [lens makers] publish on their MTT charts. One thing you pay for [with expensive lenses] is less variation lens-to-lens,” he adds.
Some Outstanding Primes
So what prime lenses would Cicala recommend? Here are a few of his favorites:
18 Optimal Prime Lenses