Extension tubes Extending the distance between the lens and the film or sensor, by inserting either extension tubes or continuously adjustable bellows, is another equipment option for macro photography. The further the lens is from the film or sensor, the closer the focusing distance, the greater the magnification, and the darker the image given the same aperture. Tubes of various lengths can be stacked, decreasing lens-to-subject distance and increasing magnification. They can be used in conjunction with some other techniques such as reversing the lens.
Close-up filters Placing an auxiliary close-up filter in front of the camera’s lens is another option. Inexpensive screw-in or slip-on attachments provide close focusing. The possible quality is less than that of a dedicated macro lens or extension tubes. These lenses add to the optical power of the lens, decreasing the minimum focusing distance, and allowing the camera to get closer to the subject.
Limited DOF is an important consideration in macro photography. Depth of field is extremely small when focusing on close objects. A small aperture (high f-number) is often required to produce acceptable sharpness across a three-dimensional subject. This requires either a slow shutter speed, brilliant lighting, or a high ISO. Auxiliary lighting (such as from a flash unit), is often required. Because of the small DOF it is essential to focus critically on the most important part of the subject, as elements that are even a millimetre closer or farther from the focal plane might be noticeably blurred.
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