What is the difference between a step-up and a step-down ring?

I want to put a large diameter filter on a small diameter lens.

Do I need a step-up ring or a step-down one?

up vote 7 down vote accepted

A step-up ring allows you to fit a filter that has threads larger than your lens. A step-down ring does the opposite (with possible vignetting issues).

If you have 72mm lens threads and want to fit a 77mm filter, you need a step-up ring. If you have 77mm lens threads and want to fit a 72mm filter, you need a step-down ring.

So in your case you want a step-up ring.

  • 1
    To be clear, it might seem like you can just reverse a step-up ring to get a step-down ring, except that the directionality of threads means that this doesn't work. (And you can use the direction of threads to identify whether a given ring is step-up or step-down.) – Hao Ye Feb 19 '15 at 22:06
  • Just note that step down rings are usually not recommended because the ring can show up in the shot and you will have to crop the picture. – Nelson Feb 20 '15 at 4:44
  • Yes that's the vignetting I mentioned – MikeW Feb 21 '15 at 8:49

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