[pathdoc]

Just making sure I'm getting this straight.

As I understand it, if the filter thread on my camera is 52mm and the filter I want to use is 55mm, then I need a step-UP ring. Likewise if for some reason I want to use a smaller filter than the lens's thread, I need a step DOWN ring.

Is this right, or have I got it backwards?

[willskywalker93]

that is correct, I used to used a 52 to 72 step up frequently. You can get the stacked kind, but those vignette on wide angle lenses, though 52 to 55 is just a single ring anyway. If you do them properly, single step up rings should not vignette unless on ultrawide lenses, but step down rings will cause vignetting in most cases, only occasionally not when using a full frame lens on a crop sensor body. Feel free to correct my if I am wrong there, but that is my understanding.

[pacerr]

Hint: Step up or down FROM the lens thread TO the filter thread -- from what's closest to ya to what's farther away. For some reason the UP or DOWN thing always seems to add a confusion factor.

[Al_Kahollick]

that is correct, I used to used a 52 to 72 step up frequently. You can get the stacked kind, but those vignette on wide angle lenses, though 52 to 55 is just a single ring anyway. If you do them properly, single step up rings should not vignette unless on ultrawide lenses, but step down rings will cause vignetting in most cases, only occasionally not when using a full frame lens on a crop sensor body. Feel free to correct my if I am wrong there, but that is my understanding.

You're understanding is correct. This is why it's wise to buy a filter for your largest diameter lens, then use rings to adapt them to you smaller diameter lenses.