Lens Primer - Creative Controls
- Aperture and Depth of Field
- Perspective and Spatial Effects
- Exploiting the Angle of View
- Lens Signature
- Other Effects
So what's in a lens? It just forms an image on your medium of choice with a few simple controls - namely focus and aperture, right? While that's certainly true and the simplest way of expressing its function, there's a lot more to a lens than meets the eye. Besides the photographer's vision and control, the lens has the most significant effect on the final image. More so than whatever body you choose, the film you load or how many megapixels the sensor has. This article is the second in a series on lenses and will delve into various characteristics of lenses and how they affect the image.
This is an obvious one, so we'll just get it out of the way first. Just about every image has a subject, surrounded by the foreground and background. It's generally accepted that your subject should be in focus and everything else to varying degrees (controlled by the depth of field). Your subject is either in focus, or it's not. So there's little in the way of creative control when it comes to focus? Not completely. Sometimes you might want to create an abstract image, with no clear, traditional subject/background components. This can be done by intentionally focusing at the lens' minimum or maximum focus (infinity) distances and shooting wide open. The effect varies, but generally you end up with a blurry wash of colors. Why would you do such a thing? Consider the following photographs - in the first, the subject is considered in focus - and out of focus (completely) in the second (which was actually used as a holiday card):
Another creative approach to focus is exactly what it is you're focusing on. That is, perhaps not the most obvious subject in the scene, either to call attention to it or to separate it from its surroundings. Consider the following examples:
In the first shot, the obvious subject is not what's in focus, but rather the glowing logo of the laptop. This in itself can often make for interesting photographs, by calling attention to something in a scene that might not otherwise be noticed or to make a statement. In the second photo, the obvious subject is in focus, but notice how it stands out from the background. This technique relies on the next creative control - aperture and depth of field.
Aperture and Depth of Field
A camera at its most basic level needs three controls; focus, aperture and shutter speed. As you can see, two of these are lens-related! Aside from focus, perhaps even more so - the aperture is responsible for the greatest effect on your photograph (and to a lesser degree, the shutter speed). We're not talking about exposure, but more so in the creative sense. The aperture you select determines the depth of field, or how much of a scene will be in focus. Wider open, say at f/2 - a lens will generally have a shallow depth of field. As you stop down, say to f/8, the depth of field deepens.
Besides the aperture - the exact depth of this in-focus zone depends on two variables; the focal length of the lens (its magnification) and the camera to subject distance. Shorter focal lengths generally appear to have a greater depth of field than longer focal lengths. As with perspective, this is a bit of an optical illusion and has everything to do with magnification and camera to subject distance. If you keep your subject the same size with either lens, you'll have the same depth of field! We tend to use our lenses a little differently most of the time and thus the effect. The depth of field is roughly centered anywhere from on your subject (with equal amounts in focus both in front of and behind your subject) to about one third in front, and two thirds behind.
As you can see from the above photos, there is very little that's actually in focus. This is a direct result of using a lens wide open, or at maximum aperture - which results in a shallow depth of field, especially on a fast lens. Fast lenses, or those that offer larger maximum apertures - have a broader range of control over depth of field over slower lenses - which often don't open wider than say, f/2.8 or more. This is one of the aspects of fast lenses that make them attractive.
Depth of field then, is an important aspect of creative control by either isolating your subject or allowing everything in the scene to be in focus - something you might see in a typical landscape shot, for example. Consider the following two photographs. In the first, attention is called to the tree and the distraction of the background is limited by throwing it out of focus. The second photograph on the other hand, focuses more on the background object and tries to remove some distraction of the tree in the foreground:
Perspective and Spatial Effects
The focal length of a lens doesn't just describe how wide an angle of view it captures of a scene, but also how that scene might appear spatially. As mentioned before, short focal lengths (wide angles) exaggerate spatial distances whereas longer focal lengths (telephotos) compress it. How does this perspective effect work? Assuming you keep your subject the same size across two different shots, a wide angle lens will produce an image where the subject and background appear farther apart. That is, the background recedes more dramatically, creating a sense of exaggerated perspective. A telephoto on the other hand, seems to flatten perspective. The background can often appear to be right behind the subject rather than way off in the distance and objects even seem to increase in size visually.
On a more technical level, the perspective really only changes as a function of the distance from the camera to the subject rather than by focal length. That is, if you take a picture of a subject with both a wide angle and telephoto lens, and crop the wide angle shot to what is seen in the shot from the telephoto - they will be identical! An important distinction, but we generally tend to use lenses differently, and thus the sense of perspective.
Consider the following examples; in the first, by using a wide angle lens and getting down low to your subject, the sense of perspective is exaggerated. In the second photo, a telephoto lens was used (at a bit of a distance) but notice how the scene appears flatter, or more compressed:
This effect is perhaps best demonstrated by a scene from the 1958 Alfred Hitchcock movie Vertigo. In this scene, the focus is on Kim Novak as the lens is slowly zoomed out while the camera dollies (rides forwards) to keep her the same size in the frame. What you can see happening is that the background seems to stretch out and move away from her. This scene couldn't be more representative of the feeling of vertigo!
Perspective is especially enhanced or downplayed then by the position of the camera within the scene. This is because you're not only changing the camera to subject distances but creating forced perspective. For example, by getting close to your subject and perhaps a little low - you can emphasize the differences in scale from the background, such as far off mountains. A wide angle lens would exaggerate this effect. Conversely, if you back up a little and use a normal lens, the scene tends to "flatten" out a little. This would be normal perspective; another reason a 50mm is considered "normal" as it reflects what the human eye sees. Take this same shot with a telephoto - which requires stepping back even further from your subject and the reverse starts to happen. The mountains in the distance now look larger and closer to your subject. That is, the scene "flattens" out even more.
Exploiting the Angle of View
A wide angle lens isn't just about getting the whole scene in front of you in a picture. For example, a vast landscape with far off mountains. Your first instinct might be to grab a wide angle and snap away. You certainly can, but it's neither creative - nor does it usually result in a great photo. Details are often too small to make out or the scene becomes overwhelming and you're not quite sure what to look at. Naturally, certain landscapes benefit from this and is perhaps the only way to really photograph them.
Let's consider how we can abuse a wide angle creatively. As mentioned above, they can be used to enhance a sense of perspective and impart greater depth of field over longer focal lengths. Use both characteristics to your advantage - and instead of trying to fit everything in - get up close! Make your subject larger and take center stage in the photograph. This is often a much more interesting picture. Instead of seeing a tiny stream in a large field, approach it from an ant's point of view. The power of the raging river up close and personal, something tangible and in your face. The grass and mountains are still there, but they're off in the distance. As an ant, you can conquer those later...
Telephotos work much the same way, albeit in reverse. Suppose you want to exaggerate just how many telephone poles line a street. With a wide angle or normal lens, you might see one or two - the rest get lost in the distance. Use the spatial compression and exaggeration of size and perspective to make them more obvious! One scenario where this works especially well is a subject shot against a sunset. By using a telephoto, instead of the sun being a far off, distant little ball of fire - a telephoto will bring it closer, making it appear larger. Much more dramatic and interesting! Consider the following two examples, which show the different approaches:
Some terms you might come across regarding lenses might be the "signature" or "rendering" of a lens. In a nutshell, these terms relate to how a lens represents or "draws" an image. That is, how sharp is "sharp?" Does the lens vignette in the corners wide open? What does the background blur, or "bokeh" look like? Is the tone of the image neutral, or does it tend towards warm or cold? All of these describe particular aspects of a lens' optical performance, but when taken together - represent the "signature" of a lens. Most people generally never notice such things. An image is simply, "nice." Photographers, especially those with an interest in the technical side of lens performance of course, do.
Most lenses, when stopped down to mid-range apertures and beyond tend to look more and more alike, even under critical inspection. Especially newer, more modern lenses. You could almost say, "at f/8 every lens is good" and you wouldn't really be wrong. Where lenses exhibit their most extreme character then, tends to be more towards wide open. This is when depth of field, "bokeh," vignetting, distortion and other characteristics are particularly or most noticeable. Remember from the first article, that it's easier to design excellent slow lenses than it is to design good fast ones. This is because fast lenses tend to have increased aberrations. How well a lens designer corrects these aberrations lends to a lens' signature.
One thing that often has a direct effect on signature is the age of a lens and its design. That is, older or "vintage" - and new, "modern" lenses often have a different look to them. This is due to the advent of newer, better materials and design as well as manufacturing techniques. Things such as lens coatings, aspherical elements and exotic materials as well as better design through powerful computers available today have changed what a modern lens is capable of. Some folks prefer the softer, lower contrast look of vintage lenses whereas others may prefer the sharper, more contrasty look of modern (often described as "clinical").
How does a lens' signature affect your creative control? First off, by imparting a mood to your photograph. Typically in landscapes, it is preferred to have a very sharp lens with good contrast and saturation. Other times, such as in portraits - especially of women or older people - it is preferred to have a softer look. You don't want to see every little detail such as stray hairs, wrinkles and other skin blemishes. Consider the following images; the first shows a darkening of the corners (vignetting), smearing of corner detail (curvature of field and spherical abberrations) and a somewhat "energetic" looking background blur (bokeh). The second image on the other hand, represents a more modern and technically perfect look whereby the image is evenly illuminated, it's sharp all over from the center to the corners (flat field), has a generally high contrast (micro and macro) and nicely saturated:
There's also the contrast of a lens to consider as to how it relates not only to your subject matter, but also to your medium of choice. With black and white film - you can use colored filters to adjust how a scene is represented and to a degree, the contrast. This isn't really possible with color or slide film, so the contrast of your lens becomes more important. And although you can adjust contrast of digital images quite easily during post-processing, it's a bit unique as far as dynamic range goes; the range from pure black to pure white. It's often undesirable to "crush blacks" and "blow highlights" in digital photography - something lower contrast lenses help to avoid (and a subject for another day).
Related to contrast is flare control. Newer lenses and designs tend to handle flare better than older ones. You may have heard of the "Leica glow" in some vintage Summilux lenses, for example. In part, this is due to veiling flare, which serves to lower overall contrast as a side effect. More modern versions no longer do this due to improved coatings, internal baffling and other design revisions. Shooting a subject against a light source (also called "contre-jour") can often lead to interesting flare effects - from an overall lower contrast and light washing over your subject - to a well-defined "sun star" in an otherwise contrasty image with no flare visible. Another visible effect of flare is multi-colored shapes (arcs and blobs) in your image, which are reflections of light from internal lens elements bouncing around. Most of the time you don't want it, sometimes you do - and can be taken advantage of as a creative tool.
You could almost say that a lens with a lot of flaws has "more signature" whereas a modern lens, which is more clinical - lacks it. It's not that the modern lens lacks signature - it's just that it has a different one. Think of a lens signature like a general description of how a lens/design performs. For example, "the Sonnar look" or "the Noctilux look." Both describe the general way these lenses render a scene. Modern lenses or those stopped down a ways tend to lose some of these characteristics, which does change the signature - but doesn't eliminate it.
There are some other effects possible by manipulating a lens. One effect, though impossible on a rangefinder (as there are no zoom lenses on this platform) - is created by zooming during the exposure. This causes a sort of streaking/smearing in space of your scene. It could be argued that this effect should be left to sample photos in a 1970's photo book...
Filters are another way to control your scene (though are technically an accessory placed in front of a lens). Diffusion filters soften your image through a variety of methods; speckles of white or black on an otherwise clear filter, a fabric screen or mesh or even Vasoline smeared on a clear UV filter. Fog filters are similar, but the effect is often in a gradient to simulate depth. Star filters are another option and are basically lines etched into the filter to form 4-point, 6-point and even 8-pointed stars out of specular highlights. Most of these are better used with SLRs where you can actually gauge and adjust the effect as you're looking through the lens. Filters which are of a solid color - can be used to change color representation and contrast in black and white photography or those of no color, considered "neutral density" filters, can be used to simply decrease the amount of light coming into the lens though varying shades of gray.