It seems like a no-brainer: a lens protector protects your lens, so of course you want to stick one on the front of your expensive optics. After all, with filters costing as little as 20 bucks, why wouldn't you attach one to protect a lens that may have cost 100 times that amount?
However, a lens protector doesn't just protect your lens; it also adds an extra, much cheaper and non-optimized element to the front of your precision-designed lens – which has been painstakingly designed with a complex optical formula consisting of precisely measured and machined, premium-quality glass elements. A far cry from the 20-buck chunk of protective plastic that you'll slap on the front.
It's for this reason that I've never used lens protectors. Let's take my Canon RF 85mm f/1.2L, for example. This is a lens that contains 13 premium glass elements in 9 groups, with Blue Spectrum Refractive Optics, and Air Sphere and flourine coatings on the front element.
Canon spent years engineering this lens to work within incredibly precise tolerances, based on exact calculations involving these 13 elements and special coatings. So, sticking a lens protector on the front interferes with those tolerances, reduces that precision, and undermines the quality of this sensational lens.
Lens protectors are a waste of money, then, right? Well, that depends. You see, the technician in me really doesn't want to stick a cheap element on the front of a lens that costs three grand. But there's the rub; the lens costs three grand. Which means if you get a scratch, a nick or – god forbid – a crack in the front element due to any kind of accident, you're in for a very steep repair bill.
Here's a thing. When I was doing my photography apprenticeship, my mentor told me that a lens hood was all the protection I needed – because short of something somehow flying directly into the middle of the hood, it would prove just as effective as a protector.
That's true; it's incredibly rare for the front element to take knocks or scrapes with a hood on. However, this advice doesn't account for something else: the expensive, and sometimes delicate, optical lens coatings.
Even the act of overzealous lens clothing can wear away these coatings; add in salt water, sand, dirt, dust, and all the other grime that comes from shooting in different environments, and those coatings may not last long at all.
So then… are lens protectors actually worth it? I never thought so. But upon looking at the sorry state of the coatings on front of some of my lenses, I'm starting to change my mind. Just make sure to buy a good quality filter so that it causes minimal compromise to your image quality.