Lenses
“Macro” lenses are generally available from 50mm to 200mm in focal length. Some shorter focal length macro lenses are appearing for small sensor digital cameras, 40mm for the Nikon DSLR’s and 30mm for the Sony DSLR’s. These are generally fine optics, but remember that they provide relatively short working distances. It is not necessary to buy lenses which are produced by the manufacturer of your camera, either. Tamron, Sigma and some other lens manufacturers make excellent macro lenses, and they are usually less expensive than the big camera makers’ offerings. It is also worth checking the larger used equipment stores to see what they have for macro optics.
All lenses are designed and built within certain constraints. People have to be able to afford to buy them, and the manufacturer has to make money on them. Therefore, there are tradeoffs in any lens. The lens designer does what it is possible to do in the design, but every lens has a so-called sweet spot, an optimum aperture where the lens delivers the best image quality it can. Usually this sweet spot is two or three stops smaller than the wide-open aperture of the lens. At the widest aperture, the lens will have more aberrations overall and somewhat less sharpness at the frame edges. At the smallest apertures, the lens is probably well-corrected, but diffraction becomes more of a problem and the lens is not as sharp as at the optimum aperture. In a zoom lens, there may be different optimum apertures at different zoom settings.
Depending on the lens and what you are doing with it, you may need to take this lens characteristic into consideration in your photography. The only way to know for certain about your lens is for you to test it. There are any number of lens measurements possible, and people argue endlessly about their value and meaning. For myself, there is only one sort of lens test that has any meaning, and that is for me to take pictures and see if the lens works for me. Other people’s test data tells me nothing really useful.
All lenses are designed and built within certain constraints. People have to be able to afford to buy them, and the manufacturer has to make money on them. Therefore, there are tradeoffs in any lens. The lens designer does what it is possible to do in the design, but every lens has a so-called sweet spot, an optimum aperture where the lens delivers the best image quality it can. Usually this sweet spot is two or three stops smaller than the wide-open aperture of the lens. At the widest aperture, the lens will have more aberrations overall and somewhat less sharpness at the frame edges. At the smallest apertures, the lens is probably well-corrected, but diffraction becomes more of a problem and the lens is not as sharp as at the optimum aperture. In a zoom lens, there may be different optimum apertures at different zoom settings.
Depending on the lens and what you are doing with it, you may need to take this lens characteristic into consideration in your photography. The only way to know for certain about your lens is for you to test it. There are any number of lens measurements possible, and people argue endlessly about their value and meaning. For myself, there is only one sort of lens test that has any meaning, and that is for me to take pictures and see if the lens works for me. Other people’s test data tells me nothing really useful.
