Looking at the World through Fish Eyes
Professional photographers often spend a premium to get lenses free of distortion in order to get the best images possible. The unique curved perspective created by fisheye lenses is a notable exception. That curved perspective can also be a lot of fun to play with and is the subject of this week's PhotoTip.
All fisheye lenses produce a round image, as do all lenses of other types. The only issue is how much of that resulting image circle fits within the frame. With most lenses, this circle is cropped on all sides and we end up with a rectangular image. Not necessarily so with a fisheye lens. Based on how much of the frame they fill, there are two basic types of fisheye lenses.
Circular fisheyes create a circular image. They have an angle of view around 180 degrees across the width of the frame and don't crop at all across the length of the frame. The full image circle thus fits within the area captured by the camera's sensor. The use of a circular fisheye results in a round image floating in the middle of a black rectangular frame. A typical circular fisheye will have a focal length of about 8mm for a full 35mm format (film, Nikon FX and similar). In the Nikon DX format, you'd need something around 5.5mmm focal length if you could find it.
By contrast, a full frame fisheye has an angle of view slightly less than a circular fisheye. They still cover around 180 degrees, but only when measured diagonally across the frame. They average only around 140 degrees when measured across the frame width. Thus, the round shape is just barely cropped out of the frame all the way around, resulting in a rectangular image. This will take a lens with a focal length around 16mm for full frame, or 10.5mm for a Nikon DX sensor.
So what do you do with a fisheye lens? Well, basically anything you want to. A fisheye can be great fun if you are a creative type. I have the Nikon 10.5mm DX fisheye and love it.
When you first get a fisheye you will probably find it difficult to get images that don't look like they were taken in an amusement park fun house or all of mirrors, but things will improve with a bit of practice. The basic problem is that everything is curved. Yes, that's partially the attraction of getting a fisheye in the first place, but too much of a good thing can be, well... too much. If everything in the frame is bizarrely curved, the image may perhaps be humorous, but it is unlikely to be all that compelling. What you want is an image that looks almost normal, but a bit exaggerated.
Since you can see the fisheye effect in the viewfinder, it can be fun to explore the world while looking through the camera and see what you can find. The closer you get to something the more pronounced the effect will be but I should warn you not to bump into your subject. A fisheye will focus down to just a few inches so be careful out there. The curved effect will also be more pronounced the closer something is to the edge of the frame. A straight line such as the horizon will remain straight so long as it bisects the image right down the middle, parallel to the frame edges. But the moment you pan the camera up or down it will start to bend. Place the horizon near the top of the frame and it will curve as if you have somehow captured the curvature of the earth itself. But the same is also true for other lines that we normally perceive as straight. If that horizontal line were a fence rail instead of the horizon, it will look mighty strange curved so drastically. Trees can also be problematic since we normally see them as straight up and down rather than curved. Thankfully, some of these issues aren't unsolvable with a bit of thought and a small movement of the camera. The closer your subject is to the front of the lens, the smaller the movement needed to shift what you see in the viewfinder one direction or another. Work slowly and methodically and the rewards will be evident in your images.
One problem that can be hard to deal with though is your own shadow or that of your tripod and camera. If the sun is behind you anywhere, it will likely be casting a shadow into the frame. The angle of view captured by a fisheye is so large, that outdoor photography with one can create frustrations that indoor photographers just don't have to contend with. A bit of ingenuity with your tripod position together with the use of a long cable release can help, but sometimes you'll just need to come back at a better time of day when the sun has moved to another part of the sky. It is also entirely possible to hand hold a fisheye since the standard guideline of one-over-focal-length yields surprisingly long maximum shutter speeds for sharp images.
Plenty of software exists to correct fisheye images to produce straight lines instead of curves but I personally don't see much point in this approach. If someone wanted a rectilinear image, they are probably better off using a rectilinear lens in the first place, not a fisheye. All such software works by appropriately stretching out and flattening the captured image and crop the result back to a standard rectangle. As such, a portion of what you originally captured (in some cases a substantial portion) is lost in the process. Your resulting image will therefore have been captured using fewer megapixels than your camera natively has, and will have a lower resolution than would be the case had you used an equivalent rectilinear lens. Composition gets more difficult if you intend to "correct" your fisheye images in post processing as well since there's no easy way to know where the final edges of the frame will be.
The bottom line is that a fisheye lens can be a lot of fun, and since they don't take up much space in your camera bag it can be worthwhile taking one with you just in case the mood strikes.