What is a Diopter?

Macro lenses are designed to capture close-up images

If you have a SLR or DSLR camera in your possession and shoot a lot of close-up photos, you'll probably already have a macro lens. Macro lenses are designed to capture close-up images. (A macro lens does not imply that it will focus close - it it just produces large images of small subjects. A technical definition exists that I will not go into here, because it's terribly confusing when it is applied to digital cameras.) However if you own any type of camera besides an SLR, your must use the lens that is installed on the camera. This is where you can use a close-up-lens (diopter).

 Close-up lenses (also called supplementary lenses or Close-up filters) typically screw on the filter thread of the primary lens, and are manufactured and sold by suppliers of photographic filters

Diopter is a measurement of a power of a prism or lens. The diopter (sometimes called dioptrie) is typically abbreviated as D. It has a dimension which is a reciprocal length, while its unit measurement is therefore a reciprocal of 1 m (3.28 ft).

The diopter will add a little magnification to your picture. If you focus using the same location using the identical zoom with both and without using the diopter, The image seems a little larger when using the diopter. (At some settings, a +5 diopter will add almost a 20% magnification.) This is nice, but is really not the point here.

The real point is that using a diopter alters your lens's focus range. Diopters are made in powers beginning at +1 through +5. Also they are stackable: you can mount a +2 diopter with another +2 diopter, and conveniently end up with an effect identical to a +4 diopter. (There seems to be no suffering of quality by stacking.) The larger the number is, the more power the diopter has. The more power the diopter, the nearer you are able to focus. To obtain specs: divide 100 centimeters into the power of the diopter. This is the maximum diopter focus distance. A +5 diopter will focus at 20 centimeters or less, while a +2 diopter will focus at 50 centimeters or less.

Schnepfenfliege Rhagio scolopaceus
Schnepfenfliege Rhagio scolopaceus (Snipe Fly)

Although it's only a rough guide, the actual results cn vary depending upon your lens and the distance you've zoomed out or in. The first thing you'll become aware of is that you are no longer able focus to infinity. In reality, if you're further away than 8.5 inches from your subject, there is no way you can get your subject in focus. Although this is not as terrible as it sounds: the front of your lens is around 7 inches distant from the back side of your camera, so you only need to get your camera to approximately 15.5 inches. I can hold my camera 20 inches from my body and not exert much effort, so I need to move my torso to approximately three feet from my subject. Really pretty easy.

Different from extenders, which are inserted between the lens and camera body and multiply the original lens's focal length, close-up lenses are attached to the filter threads of a lens, much the same as a filter. Identical to extension tubes, close-up lenses do away with infinity focusing by reducing the limit of close-focusing for the original lens.

Different than an extension tube, by not creating any loss of light. And, when used in conjunction with a zoom, diopters preserve the focus while the lens becomes zoomed in or out. (Zooming a lens with an attached extension tube drastically alters the focusing distance.) These characteristics, along with the fact that diopters often deliver increased magnification factors than extension tubes with lots of working distances in the same time setup, make diopters much easier to employ than using extension tubes for doing close-up work in conjunction with zoom lenses.

Close up lenses are not all equal. Avoid single-element close-up diopters - even when they are promoted as "multi-coated", they can diminish your image quality. (You've just spent lots of money for a quality digital camera - now , don't be a cheap skate by trying to save $40 on a diopter!) Stay with the two-element diopters. Hoya makes great quality +3, through +5 two-element close-up lenses, which can be purchased on-line.(see the bottom of this page). You might also try the typically less costly, although still excellent Canon 500D and 250D. The Canon 500D is a +2 diopter, while the Canon 250D is a +4 diopter. Quality double-element diopters, such as the Canon 250D and 500D, deliver superior image quality from edge to edge by stopping down to your lens's the optimum aperture, which is typically around f/11 through f/16. Settings such as these are easy to attain using medium speed high-quality transparency films or digital (ISO 50~100) when using electronic flash units.

Nikon also manufactures excellent double-element diopters such as the 6T, however you will need a 62mm to 58mm step down adapter to use on a 58mm thread lens because they are only made in 62mm thread sizez. Marginally improved image quality can be achieved by using a genuine macro lens, although you must work harder for it, as unlike a zoom /close-up lens combo, with a macro lens you need to move further or closer from your subject to regulate magnification. updated article Nov 17, 2011

Taking great pictures using close-up lens with Bryan Peterson

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