Macro Lens Guide

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Macro is the photo op that’s always available: You can find good close-up subjects just about anywhere. All you need is a way to make your camera focus close enough.

Dedicated macro lenses are the best option because they can focus from infinity down to close enough to produce a life-size (1:1) magnification at the image plane. Macro lenses also are optically optimized for close focusing distances, so they produce better results at such close range than nonmacro lenses used with extension tubes (and, of course, lenses with extension tubes attached can no longer focus out to infinity). Most macro lenses also are well corrected for flat fieldwork, such as photographing stamps and coins, which may or may not be useful for nature photography. The main drawbacks of macro lenses are that they’re generally bulkier and more costly than nonmacro lenses of equal focal length, although the differences today aren’t nearly as great as they were some years ago.

Nikon AF-S VR Micro-Nikkor 105mm ƒ/2.8G IF-ED; Canon EF 100mm ƒ/2.8 Macro USM; Nikon AF-S DX Micro-Nikkor 40mm ƒ/2.8G

What Makes A Macro Lens A Macro Lens?
There are a number of things that make macro lenses different from nonmacro lenses, but the biggest is that macro lenses can focus much closer than nonmacro lenses. Additionally, macro lenses are optically optimized for very close focusing distances, although most also perform very well at “normal” shooting distances, too.

Early macro lenses had extended focusing mounts, which allowed the user to position the front elements farther from the image plane, by rotating the focusing ring, than was possible with nonmacro lenses. Some macro lenses today still use this model. This is simple and produces increased magnification, but means the physical length of the lens increases considerably as it’s focused closer—and that could result in the lens casting a shadow on the subject or even striking it.

Newer macro designs employ optical formulas that allow for life-size magnification without moving the front element farther from the image plane. Internal focusing moves inner elements to focus. Doing this with appropriate elements and groups also allows for a closer minimum focusing distance and a more compact design. Since the internal elements are smaller and lighter than the front element, this also makes things easier for the AF motor, producing quicker autofocusing.

Macro lenses generally employ floating designs, with additional groups of elements that move during focusing to counter aberrations at close focusing distances. Floating elements and internal focusing alter the focal length, decreasing it as focusing distance is reduced, but for practical purposes, this doesn’t matter: A macro lens still will provide 1:1 magnification at its minimum focusing distance.

Curved lens elements project a flat subject as a curved one, so when the center of the image is in focus, the edges are out of focus, and when the edges are sharp, the center isn’t in focus. Stopping down increases depth of field and depth of focus, and thus reduces the problem, but most macro lenses are better corrected for this curvature of field than are nonmacro lenses. This correction requires additional lens elements and groups, increasing the bulk and complexity of the lens, but it’s also one reason why macro lenses are much better than nonmacro lenses for photographing flat subjects.

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Magnification
When we talk about magnification regarding macro lenses, we’re talking about magnification at the image plane. You can blow up the image well beyond that on your computer monitor or in a print, of course, and that can make the macro subject much bigger than in real life—even if you shot it with a nonmacro lens. But the macro lens gives you the advantage of more pixels recording the subject instead of being thrown away. The image of the subject will be recorded bigger in the frame, with the potential to reveal more detail.

Some confusion exists regarding a lens’ magnification on full-frame vs. APS-C-format DSLRs. The lens’ magnification doesn’t change when you switch it from one camera to another—say, from a full-frame Sony A900 to an APS-C Sony A580. A given lens focused at a given distance produces a subject image of a given size at the image plane. This doesn’t change because you place a larger or smaller piece of film or image sensor at the image plane—the subject’s image is still the same size at the image plane. A 100mm macro lens focused at its minimum focusing distance reproduces a 1⁄2-inch subject a 1⁄2-inch high at the film plane, and that image will be a 1⁄2-inch high regardless of film or sensor size.

Sigma 150mm F2.8 EX DG OS HSM APO Macro; Pentax D FA 100mm ƒ/2.8 Macro; Tamron SP AF60mm F/2 Di II ; Sony 50mm ƒ/2.8 Macro; Tokina AT-X AF 100mm ƒ/2.8 Macro PRO D

The confusion arises because the size of the image frame varies with sensor format. A full-frame sensor measures 24x36mm, or about 1.0x1.5 inches. An APS-C sensor measures around 15.7x23.7mm, or about 0.6x0.9 inches. That 1⁄2-inch-high image of the subject will take up half the height of a full-frame sensor, but nearly all of the height of an APS-C sensor. So for practical purposes, you do get more magnification with the smaller sensor—the subject fills up more of the image frame. But the actual magnification produced by the lens at the image plane doesn’t change—it’s the amount of that image that each sensor size sees that changes (see the macro lens diagram).

Macro Lens Focal Lengths
Macro lenses come in a number of focal lengths. In 35mm film days, these generally were normal (50-60mm), short tele (90-105mm) and tele (180-200mm). This still holds true today, and the results are the same with full-frame digital SLRs.

The full-frame macro lenses also can be used on APS-C DSLRs (assuming compatible mounts, of course), the smaller sensors’ 1.5x-1.6x crop factor effectively turning them into 75mm, 150mm and 300mm lenses for framing purposes. There also are macro lenses designed specifically for APS-C DSLRs; some of these come in shorter focal lengths to account for the APS-C crop factor and provide equivalent fields of view to the full-frame trio.

In any event, you’ll choose a normal, short telephoto or telephoto macro lens to suit your needs. Why the different focal-length categories? Each provides a different working distance, and thus a different perspective.

A normal (50mm for a full-frame camera) macro lens produces its 1x magnification at a distance of around seven to eight inches, a short tele macro lens (100mm for a full-frame camera) at around 12 inches and a tele (200mm for a full-frame camera) at around 19 inches. Shooting closer to the subject expands perspective, while shooting from farther away compresses it.

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Here’s an example of a macro lens focused at infinity and the same lens focused for closeup macro work. You can see how a slight flaw or misalignment in an element near the front element would be dramatically magnified. Internally focusing macro lenses have become more common thanks to advanced computer-aided design and the ability to grind specially shaped elements. Whether your macro lens is internally focusing or it physically stretches out, the need for precision in the system remains.

Additionally, the longer working distance provided by longer macro lenses gives you more room to position your lighting, reduces the chance of casting a shadow on the close-up subject and perhaps will keep you from frightening a living subject away. Working distance is the distance from the front of the lens to the subject; minimum focusing distance is the distance from the focal plane to the subject when the lens is focused at its closest distance.

Canon offers a specialized macro lens. The MP-E 65mm ƒ/2.8 1-5x can set magnifications from 1x to 5x (it can’t focus out to infinity, however) for really close shooting. Outdoor Photographer Wildlife forum contributor Dalantech has posted some fine examples of what this lens can do (search for dalantech in the Wildlife forum).

Macro Depth Of Field
Most normal and short tele macro lenses have a maximum aperture of ƒ/2.8, while most tele macros have a maximum aperture of ƒ/3.5 or ƒ/4. Due to the limited depth of field at macro shooting distances, these apertures let you produce dramatic selective-focus effects; focus on a particular part of a flower or the eye of an insect, and everything closer to the camera or farther away blurs nicely.

If you want an entire insect or flower to be sharp, you’ll have to stop the lens way down to increase depth of field. Even then you probably won’t get the entire subject sharp due to the very limited depth of field at very close shooting distances. Stopping the lens way down introduces the effects of diffraction—at very small apertures, light bends around the edges of the aperture, reducing overall sharpness, even as increased depth of field increases it.

Most professional macro photographers use electronic flash to illuminate their subjects. Electronic flash offers two major benefits; it’s bright at macro range, allowing you to stop all the way down to increase depth of field, and its very brief duration at short range (1⁄10,000 sec. and shorter) minimizes the effects of camera shake and subject movement. Special macro flash units mount on the lens and allow you to set them to provide even lighting or directional lighting.

Focusing Macro Subjects
Most macro lenses in production today offer autofocusing, but it’s generally best to focus a macro subject manually. That’s the only way to be sure focus is exactly where you want it. If a particular magnification is desired, set that (most macro lenses have magnification or reproduction ratio reference markings on the barrel), then slowly move the camera in on the subject until it comes into focus in the viewfinder or on the LCD monitor if you’re using Live View mode. Once you’ve achieved focus this way, you can activate the AF system to maintain focus if the subject is moving. If you just want the biggest image of the subject, set the lens to its minimum focusing distance, and move in until the subject appears sharp in the finder. Of course, you’re free to position the camera, then adjust focus using the focusing ring or even AF, which can work, too.

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Tripod Or Handheld?
A tripod can hold the camera steadier than we can, and can lock in a composition of a nonmoving subject so you don’t accidentally change it as you squeeze off the shot. But it can be difficult to position the camera exactly where you want it for a macro shot using a tripod. So many macro shooters work handheld, using electronic flash’s brief duration to minimize blur due to camera shake. You may want to try it both ways to see which works best for your macro photography. A monopod is a good compromise, making it much easier to position the camera right where you want it, yet providing more support than pure handholding.

Canon, Nikon and Sigma offer macro lenses with built-in image stabilizers, and Olympus, Pentax and Sony offer DSLRs with built-in sensor-shift image stabilization. If you prefer to do your macro work handheld, stabilized gear will give you sharper images.

Macro Zooms
While true macro lenses focus close enough to produce a life-size image of the subject at the image plane, a number of macro zooms are on the market. These focus closer than nonmacro zooms, but don’t come close to producing 1:1 magnifications. Most, in fact, produce maximum magnifications of 1:3-1:4 (1⁄3 to 1⁄4 life-size). This still works for subjects like flowers and large insects, but be aware you won’t get life-size magnification and fill the frame with small insects as you can with a true macro lens.