Supplementary close up lenses
The least expensive accessory is a
supplementary close up lens. This single, positive glass elements screws
onto the front of a lens mount like a filter and shortens the focal
length of a prime lens, allowing you to focus closer than possible with
the prime lens alone. In addition, unlike other close up equipment, an
accessory close up lens requires no increase in exposure.
Supplementary lenses come in several
different strengths or powers from +1 to +10. As the numbers get larger,
focal lengths shorten, camera to subject distance shrink and images
increase in size. Any tow powers may be combined to produce a greater
power (+2 and +3 to make a +5, for example), but the results may not be
as sharp as a single power used alone. Combining more than two powers at
a time is not recommended. Sharpness may be further impaired, and light
may be blocked off at the corners of the frame.
On inconvenience with supplementary lenses
is that each power (single or in combination) permits focusing within a
narrow range of distance only. Therefore, it might take several of these
attachments to meet your entire close up needs. However, even then
switching them around to obtain the right distance and the desired field
of view is annoying and time consuming. If you plan to do a greater deal
of close up work at various distances, you may want to invest in a
variable focus close up lens. it is a more complex and more expensive
accessory that lets you change powers (within limits) without changing
supplementary lenses. However, for most photographers one or two single
element attachments (+3 and +4) being the most useful) are all they will
Always install a close up attachments so
that the convex (bowed out) side or the little arrow sometimes engraved
on the metal rim, is pointed toward the subject. If a filter is needed
along with a close up lens, put the filter on last. However, with the
strongest powers the outward lens curvature may be so pronounced that
the filter will have to go on first.
A close up attachment can be used with
almost any camera and any focal length lens. if your camera has ground
glass focusing, you will be able to see the field of view and point of
sharpest focus easily. But if you have a fixed focus or rangefinder
camera, you will have to measure carefully and adjust the distance
between lens and subject according to the accompanying table, or those
provided with accessory lenses.
With supplementary close up lenses overall
sharpness is not as great as that produced using more sophisticated
equipment. However, if the prime lens is stopped down at least halfway,
results are adequate for many purposes. Small stops also increase depth
of field, which is always very shallow in close up work.
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