Macro Vs. Macro Zoom

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Macro Vs. Macro Zoom

Know The Difference

by Jon Sienkiewicz

Every hobby has its own language, and photography is no different. It can take a while to learn all of the unintuitive abbreviations, unnatural acronyms, and shifting definitions. The term “shifting definition” refers to words like “automatic” which have had different meanings depending on the context and the era. Learning the language is vital to enjoying the hobby but can be a formidable obstacle for some. And misunderstanding the nuances can lead to poor purchasing decisions.

Marketing people compound this communication problem by stretching the limits of words to exaggerate certain functions and features. Most technical terms are unregulated, which means that a given company can legally use a word to mean almost anything they want. A prime example is “macro.” Many macro lenses focus to “life size,” which means that an object 1cm long in reality appears 1cm long on the recording medium. This relationship is expressed as a ratio, and life size is indicated as being 1:1 magnification, exactly the same size as the subject regardless whether it’s on film or a digital imaging sensor.


© 2009, George Schaub, All Rights Reserved

But not all macro lenses focus 1:1, but nearly all can produce images that are 1⁄2 life size (1:2). “Macro Zoom,” on the other hand, became a popular description for zoom lenses that focus close but are not—in the strictest sense—truly macro lenses.

And this is how we begin to run afoul of best practices. The FDA prohibits food manufacturers from labeling an edible product “lite” unless it meets certain criteria for reduced fat (or sodium) content, for example. But a lens maker can call any close-focusing lens “macro” with impunity. Most macro zooms are in the 1:5 or 1:4 range, and that’s really pretty good from a practical picture taking point of view. But it isn’t macro.

All lens designs are compromises. Expert designers must decide the best combination of optical performance, physical size, focusing specifications, and cost—among a hundred other variables—to create a lens that will be both a photographic triumph and a commercial success. The task of a lens designer can be compared to a housemaid who’s trying to make up a bed with a sheet that’s too small. Tuck the sheet in at the foot and the head of the bed is exposed. Tuck it in at the head and the foot of the bed is left open. On one end or the other, something’s got to give.

Most lenses are used to photograph medium to distant subjects—like portraits and landscapes—so most lenses are optimized for longer shooting distances and lower subject magnification. In general, when subject distance and/or subject magnification is changed significantly, lens aberrations are also significantly changed. If you were to use a typical lens on a bellows attachment for close-up photography, the curvature-of-field and spherical aberration would prevent you from getting satisfactory results.

On the other hand, macro lens are highly corrected for optical aberrations that prevail when focused close. And although they are optimized for macro shooting, aberrations are kept well under control even when the lens is focused all the way out to infinity.

The physical construction of a macro lens is different, too. The front element is often smaller and flatter and more deeply recessed—so deeply that the lens barrel often functions as a sort of lens shade. And, according to my friends at Sony, most modern macro lenses use “floating” or “double floating” designs. Floating design is a technology to correct curvature-of-field in close-up photography, they explained to me. The movement of certain lens element groups is controlled independently to slightly shorten the specific lens group distance. When focused near the closest position, one or more groups of elements moves into the right position for optimal results. This shift, or float, is not necessary and does not occur when focused at infinity or at medium distances.

Sony macro lenses feature an automatic clutch mechanism to prevent focus ring rotation during auto focusing. And in order to provide best “bokeh” (smooth out-of-focus image), Sony macros have a nine-blade circular aperture.

If you want a versatile lens that will perform well under a wide variety of shooting circumstances, particularly if you’re not shooting small objects from a short distance on a regular basis, by all means, go for the macro zoom. But if you mostly shoot tiny things like bug’s eyes and flower innards, stick with a real macro. Because it’s corrected for close-up shooting as well as infinity, a high quality macro is usually the sharpest overall lens you can own, all things considered.

 

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