Digital single lens reflex, or DSLR, cameras primarily use changeable lenses like their non-digital SLR cousins. In fact, all of the same lenses that can be used on film SLR cameras also work on DSLR cameras. Lens adapter tubes allow you to connect lenses of one size to cameras of another size.
Other than the use of digital imaging to capture the photos, DSLR cameras function almost identically to film SLR cameras. They use the same lenses and take in light in the same way. The single lens reflex refers to the small mirror that reflects the light coming through the lens up at a mirror and through a prism to a viewfinder. Just before the photo is taken, the mirror moves out of the way and lets the light through the lens to the imaging media. This allows the photographer to see exactly what the lens will do to the image being looked at through the viewfinder, so if a new lens is attached, the photographer can see the effects immediately and compensate appropriately.
Most lenses provide a set viewing angle. The angle refers to the size of the angle from the edge of the field of vision to the other edge. A wide-angle lens might allow a 180-degree viewing angle, whereas a narrow angle might only give 20 or 30 degrees. Usually lenses have a zoom and focus capability that allows the angle to change within a range. Other lens attachments might be color or light filters, such as a polarizing filter that reduces glare in the photographs or a dark filter for taking pictures of the sun.
Lenses screw into threads on the camera. Lens adapters are short tubes that have threads on both sides. So a lens adapter screws in before the lens, attaching to the camera, then a lens screws into the adapter, which offers a different size thread than the camera had originally. Usually lenses made by the same manufacturer as the camera do not need an adapter, but if you want to use lenses from a different maker, you will probably need an adapter.
Adapter tubes interface with lenses in specific sizes measured in millimeters (mm). The sizes can range from 46 to 62 mm. Check your camera manual and the specifications on the lens you are wanting to use before buying an adapter tube. Some adapter tubes come in several pieces to provide a range of steps, while others offer only one step. For example, you could get an adapter to step up from 42 to 55 mm or a tube that would step down from 62 to 55 or 45 mm.
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