The Purpose of a Lens Hood – If you’re not using yours, you’re missing out!
This lens flare was created in GIMP.
The main purpose of a lens hood is to keep stray light out of your lens. Stray light (extra light that doesn’t contribute to the composition of your picture) can cause lens flares. Lens flares reduce image quality, sometimes to the point of completely obscuring the subject of the photo.
Don’t get me wrong, there are times when you might want to cause a lens flare. They can add atmosphere to a photo. You can even add lens flares to your photos after the fact, by using a program like GIMP or Photoshop. But in most cases, lens flares are accidental, and they don’t improve a photo. That’s where the lens hood comes in.
The Anatomy of a Lens Flare
Stray light can come from any source. The light could be from the sun, a strong reflection, artificial light from a lamp or street light, or from a bright white background. The light source can be in the frame (in the picture) or not. Whatever the source, it’s ‘stray light’ because it’s entering the lens in an undesired way.
Normally, we want light to hit a subject and bounce directly back into the camera lens (the actual image light in the diagram above). But when stray light enters the lens at an odd angle, the light can scrape across the optical elements of the lens (AKA the glass) instead of passing directly into the lens. The light bounces around inside the lens, ultimately causing a fog, or colored circles that obscure the subject of the photo. That fog, or the colored circles you see in the final image, are the lens flare.
The Purpose of a Lens Hood
Enter the star of the show. The purpose of the lens hood is to keep stray light out of your camera’s lens. If stray light doesn’t get into the lens, you won’t have lens flares.
Lens hoods work well on telephoto lenses, since the hood can be long, without blocking the field of view.
But, a lens hood will only prevent lens flares from light that’s not in the field of view. In other words, if the sun is causing a lens flare, and you can actually see the glowing ball of the sun through your lens, the lens hood won’t help.
Lens hoods are designed to be just outside of the field of view of the lens. In other words, you won’t actually see the lens hood in your pictures. But, it should be big enough to block out the stray light that would potentially cause lens flares.
When Lens Hoods Don’t Work
Wide angle lenses and zoom lenses can be a bit of a challenge for lens hoods.
Wide angle lenses have a really wide angle of view. The lens hood has to be really short to avoid making a guest appearance in your pictures. Sometimes the hood isn’t long enough to block out all of the stray light. You might see lens flares with wide angle lenses, even though you have the lens hood on. You may be able to solve this problem with the Scott Kelby Hat Trick. (In The Digital Photography Book
On a wide angle lens, the hood can only be so long, otherwise it will block the field of view. Short lens hoods can’t block as much stray light.
The problem with zoom lenses is similar. There’s only one lens hood, but many possible fields of view with a zoom lens. The lens hood can only be as long as the widest filed of view will allow, otherwise, you’ll see the lens hood in your photos. So, there may be zoom levels that allow more stray light in that you might want.
Fortunately, there are lens hoods that are made with a sort of ‘bellows’ design. That just means you can expand or contract them to be longer or shorter, depending on the zoom level of the lens.
One last problem with using a lens hood is possible vignetting. The lens hood may actually shade the corners of the lens enough to cause the edged and corners of the photo to be darker than the center. This won’t happen with all lenses, and all lens hoods. And it’s usually less noticeable with cropped sensor cameras. Full frame cameras will have the most problems with vignetting.
Fortunately, vignetting is pretty easy to correct in photo editing programs like GIMP or Photoshop.
Added Benefit of a Lens Hood
This picture was taken with a lens hood, but since the stray light was within the field of view, the flare happened anyway.
Lens hoods are great for protecting your lens from physical damage.
Many people use clear UV filter on the end of their lenses to help prevent scratched and nicks on the expensive glass. But, cheaper UV filters can actually diminish the quality of your photos.
A long lens hood acts as a physical barrier between the end of the lens and the rest of the world. In the same way the hood blocks stray light from your lens, it can block tree branches, elbows, walls, and other hard objects that could damage you lens. I’ve even heard stories of people dropping their cameras on the hard ground. While that’s a terrifying thought, every story ends with “…the lens hood took the brunt of the force, and my lens was unharmed!”
That alone is a great reason to use your lens hood every single time you use your camera, even when you think there isn’t any stray light.
The Moral of this Story
A lens hood’s job is to keep stray light out of your lens. A lens hood may not block out 100% of the stray light that threatens to cause lens flares in your photos, but the stray light it does block will surely increase the quality of your images. While some lens hood/camera/lens combinations may cause vignetting, this is often an easy problem to fix in a photo editing program like GIMP or Photoshop.
Lens hoods have another hidden purpose. They also serve as a physical barrier between your expensive lens and the sharp, pointy world. This alone is reason enough for me to keep my lens hood on my camera all of the time. Now, this may be a matter of personal taste, and you may decide using a lens hood isn’t right for you. But, if you’re images are suffering from lens flares often, and you’re worried about bumping your lens into things while you’re out and about, a simple lens hood is the perfect solution to your problems.
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