Close-up filters (referred to as close-up lenses) screw onto the filter threads of a lens and enable you to achieve focus at close distances to your subjects. They can provide ordinary lenses with macro capabilities much like extension tubes.

Unlike extension tubes, close-up lenses contain optics, and affect the quality of your image — therefore may not be suitable for use with cheaper lenses and may lessen the quality of your expensive lenses.

A polarizing filter can eliminate distracting reflections.
A polarizing filter can eliminate distracting reflections.

100 mm, .5 sec, f/16, 100

Close-up lenses come in various levels of magnification, and these filters are lightweight, easy to store and simple to work with.

For a more professional quality close-up filter, consider using the Zoerk Macroscope. This is an aspherical (shaped in a non-spherical manner in order to work better in combination with a spherical lens) coated lens that screws on to the front of your ordinary lens.

It provides high-quality optics and can produce 1:1 ratios when combined with an 80mm lens. Because the Zoerk Macroscope has an aspherical shape, it eliminates most aberrations (flaws that occur when light is refracted through a lens) that are normally caused by using multiple lenses in one image capture.