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I'm rather new to photography, having come from an amateur hobbyist video background. I recently purchased a Sony Alpha A58, and I want to take high quality close up shots. As I understand it, I need something called a macro lens. How are macro lenses measured? Focal length?" Something else?

Finally, are there other options for using, say, a regular lens?

Moshe
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A macro lens is simply a lens that allows closer-than-normal focus. Most fixed-focal-length macro lenses will focus to a 1:1 reproduction ratio — that is, the size of the object's image on the sensor at the closest focusing distance will be the same as the size of the object itself. Some specialized lenses (notably the Canon MP-E 65 f/2.8 and the old Minolta 1-3X macro zoom) will only focus at high-magnification distances (the MP-E 65, for instance, will only produce images between life-size and 5x life-size). Zoom lenses marked "macro" may permit images that are only half life-size or 1/4 life-size.

Taking 1:1 lenses as the norm, they will all give you the same magnification. The focal length determines how far away from the subject the camera can be at a given magnification. Longer lenses can be used from farther away. In most cases, at least with live subjects, longer is better. And being further away means that your camera won't be blocking the light that made the subject interesting in the first place.

It is not necessarily true that you need a special macro lens for close-up shots. It really depends on how close-up you need to be. Most of the kit zoom lenses will get in tight enough for florals and such; it's only when you want a very small subject to take up a substantial proportion of the picture that you'd need to go to a special lens. Even there, though, you often have alternatives like extension tubes (spacers that move the lens further from the sensor), close-focus filters ("diopters"), and reverse-mounting or stacking lenses. The problem is that, unlike most macro lenses, you can't focus far away with the same set-up you use for close-focusing — you lose the ability to achieve infinity focus, and may not be able to focus more than a few inches away, depending on how radical your set-up is.

  • +1 for the whole answer, and especially to mention "extension tubes" : Those are a very, very cheap alternative to buying special lenses, allowing you to use your existing lenses and changing dramatically their focal point. @Moshe: Try one, and be amazed. (I still have to grok how to use mines, but I already know it can do wonders: I have a full frame + 1.8/85mm, which can't focus closer than 80cm away, but with some tubes I can focus at a few centimeters and have the (tiny) subject fill the sensor. You lose some quality (as it uses only portion of the lens), but with a good lens, it works! – Olivier Dulac Jul 03 '13 at 17:11