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Tuesday, August 23, 2011

Macro Lens Guide

A proper macro lens is designed to eliminate aberrations, focus colors and attain maximum sharpness on close-up subjects

Labels: LensesGear
This Article Features Photo Zoom

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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