I'm always amused when I see someone photographing with a lens hood reversed on the lens (disclosure: I’ve done it on occasion myself). Obviously, they valued having a lens hood enough to buy and carry it. On the other hand, they don't value it all because they're not using it.
Why do you use a lens hood?
Two basic reasons:
- Flare control. In particular, strong light at or just off the edge of the frame. While lenses have gotten better coatings and internal flare control over the years, there's still some veiling flare that will happen in most conditions. Sure, crank the Dehaze and Clarity sliders up on your post processing software and maybe that disappears, but why start with a defect in your image data? Moreover, light at edges cases still triggers strong flare production in most lenses. The wider the lens, the less useful the hood is in such cases, but again, why start with a defect in your image data?
- Glass protection. I tell a story about how a lens hood saved the front element of an expensive lens once, because it hit the rock first and the plastic absorbed the impact and broke first. Simply put, a lens hood is often a bumper. When you're peering through the camera with a wide angle lens, your sense of distance is off, too, making it more likely you'll poke the camera forward into something. Again, on really wide angle lenses the hood is less useful here, but a little protection is better than no protection. In light rain or misty conditions, a hood—particularly the deeper ones on telephoto lenses—can protect the front element from getting water drops on it. The lens makers have tried to help keep front elements clean of moisture by adding a fluorine treatment to the front element, but that's not at all a perfect solution. On the sidelines of wet outdoor games, that lens hood also gives me something on which to attach my rain cover.
Why don't we just use a protective filter for #2? Don’t get me started ;~). I'm not convinced that a clear (or UV or Skylight) filter actually provides any useful protection. Moreover, it impacts #1, because it increases the likelihood of flare.
