It moves the lens from the film or digital sensor. The closer the focus is, the greater the magnification. When using the extension tubes alone (10mm or 16mm ) or combination (10mm+16mm=28mm),support AF(Auto-Focus), AF Motor Protection: while using 2 rings together, we suggest you to use manual focus or Increase the lens focal lengths for it's a little bit difficult to auto-focus with 2 rings together, and also protecting your lens motor.
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