For macro photography with the Nikonos system you use extension tubes. These are rings that
fit between the prime lens and the camera body. With extension tubes, you do not require
reflex viewing for focusing; the scale of reproduction is fixed, and the subject merely
needs to be the correct distance from the lens in order to be in focus. This focal point
of a shot (and the angle of view of the lens) is shown by probes, wands, or framer
attachments. Extension tubes do, however, have the disadvantage of dictating the subject
size suitable to fill the frame and, additionally, are non-interchangeable underwater.
Other non-SLR systems do not have a detachable prime lens and so use close-up
supplementary lenses for photography of small subjects.
removing a probe on the same side as the strobe removes the probes'
shadow on the picture.