Of Lenses And Apertures

It's nice to talk about composition in an abstract sense, but you don't take pictures with abstract equipment. As a result, if you want to think about composition in a real-world sense, you have to talk about the way the equipment you use influences and even limits your compositions. That's what this chapter is all about.

Wide vs. Narrow

The most fundamental piece of equipment that affects you composition is your lens. Lenses fall into three categories, roughly. One is "normal," one is "telephoto" and one is "wide angle." What distinguishes these types from one another? Focal length. You can think of the focal length as being related to the magnification of the lens. "Long" lenses (i.e. lenses with larger focal length numbers) magnify more than "short" lenses. The focal length is actually the distance from the optical center of the lens to the film plane, but that's not important for this discussion.

"Normal" lenses, for 35mm cameras, are in the range of 28mm to 60 or 70mm. Lenses below 28mm are usually considered wide angle, while lenses shorter than 20mm are generally considered to be "superwide." Lenses longer than 60 or 70mm are telephoto lenses, while lenses longer than 200mm are "extreme" telephoto lenses.

The "wider" the lens, the larger a field of view it delivers to the film. That is, the wider a lens is, the more "left and right" it can see. For the same size subject, you have to get closer to fill the frame with a wider lens. Alternatively, the wider the lens, the larger the subject you can fit in the frame from the same distance. The "longer" the lens, the more it magnifies. Longer lenses make smaller objects appear larger on film than shorter lenses.

So what?

Well, there are practical limitations to composing pictures with lenses. For instance, wide-angle lenses make big things look small, and small things just about vanish. So trying to take a picture of a sailfin blenny with a 20mm wide-angle lens is going to give you a tiny speck of fish on a very large background. Similarly, taking a picture of a whale shark with a 60mm lens is going to get you pictures of one of the shark's spots, rather than the whole creature. So you can see that your choice of lens limits your choices as far as composition goes.

There's another implication, one you may have already encountered. If you want to take big scenic pictures, you need to use a wide-angle lens...but then if you find a half-inch pipehorse, you're out of luck. Similarly, if you want to take pipehorse pictures, you need to use a macro setup...but then if a manta shows up, you're going home with no pictures of it. Some camera systems (most notably some of the Sea & Sea cameras) allow you to change lenses under water, which alleviates some of these problems. But for the most part, you have to choose your lens before the dive, and then stick with the pictures that lens can take.

Let's take a look at a few specific lens focal lengths and see how they affect your compositional choices

Long lenses

Examples: Nikonos 80mm, Housed camera 50, 55, 60, 90, 105mm

These lenses are typically used for fish portraits and macro work. Photographers who use housings shoot lenses in these focal lengths because most of them can also do macro focusing; this makes the lens much more versatile. There is one fundamental problem with these lenses: there is a functional limit to how large a subject you can shoot with them. The reason for this is simple: they magnify too much. If you have a large subject, you have to get far away from the subject in order to fit it in the frame, and then you are too far from the subject for your strobe to be effective. The longer the lens, the smaller a subject you have to find. For instance, with a 60mm lens, the largest subject you can shoot effectively is about 2-3 feet long. With a 105mm lens, the largest subject drops to ~1.5 feet in size.

There's another effect you have to consider when shooting long lenses. They tend to "flatten" the perspective. What I mean by that is that objects that are at different distances from the camera tend to blend in together, at least in size. There's a practical compositional implication to this: you want to make sure that the background doesn't compete with your subject when you frame up the shot, because the lens is not going to help you separate the subject from the background. So when you're shooting with a long lens, be sure to look carefully at the background, and see if there's some way you can isolate your subject a little better.

Finally, long lenses, especially in macro mode, have a very small depth of field. As a result, you will frequently have to have either spot-on focus, or small apertures in order to get a sharp subject.

Medium Lenses

Examples: Nikonos 28,35mm, Housed 35-50mm

These lenses are the "jack of all trades, master of none" tools. They don't distort perspectives, they don't have great depth of field, and they're not particularly good at anything. The biggest problem I have with these lenses is that most people are after high-impact photos under water, and lenses in this range will not help you do that.

Wide Angle Lenses

Examples: Nikonos 20, 24mm, Housed 28, 24mm

Wide-angle or super-wide lenses are the lenses of choice for most photographers under water. The reason for this is simple: they allow you to get close to your subject, which removes distorting and backscattering water from between you and your subject..

Wide angle lenses distort perspective in a way opposite that of long lenses: they enhace the separation between objects by making nearby objects look much larger than distant objects. This is often really helpful, because it makes your subjects stand out from the background. When you're framing up a wide-angle shot, you have to be especially careful to inspect the edges of your frame before you shoot, because it's easy for unexpected and/or unwanted objects to creep into the frame.

Another cool feature of wide angle lenses is their minimum-focus distance. It's much shorter than that of longer lenses, which means that you can get really close to your subjects. Of course, there's a practical limit to how close you can get, imposed by (a) subject size and (b) how close the subject will let you get. But getting really close makes the subject look huge compared to other things in the frame, which is another compositional tool for you to use.

Super-wide lenses

Examples: Nikonos 12, 15mm, Housed 16, 18, 20mm

Super-wides are the Cadillac of underwater photography. They let you get within inches of your subjects, which can produce some extreme perspective distortion. They also typically introduce barrel distortion, which makes parallel lines bow out from the center of the frame--but there aren't too many straight lines under water, which often makes this effect hard to detect.

Super-wides come with their own hassles, though. Primarily, it's extremely easy for extraneous garbage to drift into your pictures when you're not looking. Dangling gauge consoles from other divers are a major offender.

Super-wides give you a great tool, though, a technique called "Close-Focus Wide-Angle," or CFWA. With CFWA, you get super close to your subject (like 12-16 inches away), using a super-wide lens. Then your subject looks huge, the background looks far away, and you get a subject that just about jumps off the slide at the viewer. Beware of the barrel distortion, though, as it can be unsettling.

There are a few compositional issues of which you have to be aware with super-wide lenses. First off, you have to be conscious of the perspective distortion, especially when using rule-of-thirds composition. If you put your subject on the thirds but something in the center of the frame is closer to the lens than your subject, it's going to look awkward because the "other" thing is going to be larger than your subject, which is generally a no-no.

Wrap Up

So there you have it: the four major types of lenses, what they're good for, and what you have to look out for. One piece of advice I have for you is this: when you dive, be aware of what type of lens you have mounted, and don't try to shoot photos that don't work well with that lens. Don't go after gobies with a super-wide, and don't try to do scenics with a 105.

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