A Quick Guide to Buying Macro Lenses
Macro lenses are available in a variety of fixed focal lengths, ranging from 50 to 200mm. Some of them focus down to 1:2 but extend to 1:1 via an optically matched adapter at an extra cost. If you have decided to take the plunge and purchase your own macro lens, here are some of the most important things that you need to keep in mind.
A true macro lens is able to magnify at the image plane. Remember that you can easily enlarge an image after you have captured it using your photo editing software. However, a true macro lens provides you with the benefit of more pixels recording subject instead of being eliminated. This means that image of the subject will be recorded bigger in the frame, and also allowing more details to be revealed. A true macro lens will have 1:1, or 1x magnification (or greater). However, keep in mind that the sensor size does not have impact on the magnification capability of the lens itself.
Focal length determines your working distance from a subject. The longer the focal length, the greater the working distance to achieve 1:1 magnification. When you have a 100mm macro, you will be twice the distance from your subject compared to a 50mm macro. If there is any risk that you might scare your subject away when you get to close, a greater focal length is desirable. Furthermore, you are also less likely to hinder ambient light on your subject.
A typical (50mm for a full-frame camera) macro lens creates a 1x magnification at a distance of around seven to eight inches. On the other hand, a short tele macro lens (100mm for a full-frame camera) is at around 12 inches, while a tele (200mm for a full-frame camera) produces it at around 19 inches.
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. This will allow you to create dramatic, selective-focus effects while shooting your subject.