Give a Man a Fisheye ...
Give a man a fisheye lens and he may take some interesting picture. Teach him to use a fisheye lens and he may take some truly compelling images.
When you first pick one up, a fisheye can seem somewhat overwhelming with its protruding glass front element bulging out almost like the beginnings of a fragile soap bubble. A fisheye lens just looks weird. Whereas most lenses have, more or less, flat front elements, the front element of a typical fisheye lens is very much rounded. You just know it's something different.
Mounting it on your camera and looking through it, your initial assessment is more than confirmed. Looking through a fisheye is even weirder than looking at a fisheye. The whole world wraps around you, presenting itself as in a carnival funhouse mirror. At first it can be almost disorienting. The horizon and everything else becomes wildly curved. How on earth is one supposed to use a fisheye lens effectively? The task seems more than a bit daunting.
Pointing a fisheye lens at various potential subjects reveals even more problems. Your shadow always seems to be in the frame. No matter where you go, there you are. Unless you're attempting to take an unconventional self-portrait, a fisheye can be a challenge. And everything looks so small. That potential subject you thought might look great becomes a tiny speck in a vast frame filled with clutter when viewed through a fisheye lens.
In truth, understanding how to use a fisheye lens isn't really that different from understanding how to use more conventional wide angle lenses. It's just that you can get away without understanding the details until you venture into fisheye territory. Regardless of just how wide the angle of view is, it's all about perspective, and perspective is all about relative distance. I've written about this before. If you aren't yet fully acquainted with what I mean, you can get the full backstory on how perspective works from this article.
Some fisheye lenses produce a round image. Others produce an image circle large enough to cover the entire rectangular frame just as regular lenses do. Of course all lenses create round images. The only issue with all of them is whether the diameter of that circle is greater than the diagonal of the image frame or not. Circular fisheye images have their place, but for my money I greatly prefer full frame fisheye images.
This field of view of a fisheye lens can approach 180 degrees. It doesn't actually shoot what's behind you, but it can seem that way. With such a vast field of view, it can be hard keeping feet, tripod legs, shadows and other unexpected elements from intruding into the frame. When shooting with ordinary lenses it's a recommended practice to scan the edges of the frame looking for intruding elements and other distractions. With a fisheye lens this becomes a requirement rather than a recommendation.
The extreme wide angle is at the root of the odd curvature of otherwise straight lines. Imagine a straight line some distance from a lens pointing perpendicularly towards it. If the angle of view of that lens is narrow enough, every point on that line seen by the lens is still roughly the same distance away. But as the field of view becomes even wider, distance to points on that line towards the edges of the frame will become ever more disproportionate to the straight-line distance to the center. And since objects further away will naturally appear smaller, straight lines get curved to compensate. This would happen to a degree with every lens but can be controlled via the design of the lens. Fisheye lenses generally exceed the bounds of what can be compensated for.
It's important when using a fisheye is to get close — really close — to your subject. Don't be afraid to position the front of the lens just a few inches away from the foreground. Without doing so, you simply won't end up with a foreground. Everything in the frame will be rendered passively far back with little to grab the viewer's attention. There are exceptions to every rule of course, but it takes a mighty big subject work without getting up close.
To downplay the curvature of the horizon, look for compositions that allow you to place the horizon in the middle of the frame. What beginning photographers are told to avoid for normal compositions is exactly the best way to compose many fisheye shots. If the horizon isn't straight to begin with you have less to worry about and can often get away with positioning it higher or lower in the frame without causing distractions. Vertical horizontal lines are less common that horizontal ones in nature but tree trunks can cause problems on occasion too. It's often a matter of juggling alternatives in the quest for the best composition.
If you do decide to go with a horizon that doesn't appear straight, this does give you a tad more leeway on not rendering it straight either. It's far less likely for the viewer to notice a crooked horizon when it isn't straight. This can allow you to slightly tilt the camera on purpose to render trees vertically near the edges of the frame that would otherwise tilt one way or the other.
Sometimes your best bet is say the heck with it can make the horizon curved on purpose. A scene with a natural curve can be accentuated all the more with a fisheye lens.
Regardless, endeavor to keep any vertical lines either completely above the frame's horizontal midline or below it. Lines above the middle will tilt one way. Lines below the middle will tilt the opposite way. Any vertical line that crosses the midpoint will lean both directions, rendering as sickle shaped arcs.
A good way to become more familiar with the quirks of shooting with a fisheye can be spending some time walking around with one. Try carefully moving through a scene while holding a camera mounted fisheye lens to one eye. Keep the other eye open so you can see where you're going so you don't trip. Or stand in one spot with a fisheye while panning up and down, or back and forth across a scene to see what happens. Move in to look up close, and then step backward to observe the effect.
When you find what you're after, the extremely short focal length of a fisheye can work in your favor. Handholding a fisheye is quite practical in most circumstances. If you're shooting in low light though, be sure to get out the tripod just as you would with other lenses.
In the end, my best advice to someone feeling intimidated by the idea of shooting with a fisheye is not to be. Especially in this age of digital, you can look through the lens and learn as you go. You can see the results immediately after each press of the shutter release if you want to. And you can delete whatever you don't like and no one will ever know. Fisheye lenses can be fun to experiment with. And the results can be eye-catching.