I just bought a new camera which comes with a lens with 67mm filter threads. I would like to use my Canon close-up filter, which has 55mm threads, on this lens. Would it be possible with a step-down ring?
Your question is pretty unclear. However, there's two possible things you could be doing and generally, they don't work too well, but can be done with the right parts.
Trying to mount a filter which is too small for the lens — this will block part of the image.
Using a lens which is too small for the camera — even if you could find an adapter to do this, the image from the smaller lens won't cover your sensor.
Either way, it's not ideal, and you're much better off just buying the correctly sized parts. Going the other way on both of those options is usually ok.
Its really a matter of the focal length of the lens and the f-stop you want to shoot at. If the lens was a longer zoom you could use a step down ring and adapt it. On a longer lens you will have a narrower field of view so you will be less likely to see the step down rings in the edges of the frame. That doesn't mean you wont get some darkening in the corners though. You have to realize that the step down ring is now blocking out some of the lens and reducing the amount of light let in. That's why you will need to pair this with a small aperture to avoid vignette. All that being said its really not a great plan. I would say you are better off even buying a cheapo macro filter off ebay that is the right size. This will most likely result in higher quality than using the step down ring. Granted you would be better off yet if you got a quality macro filter that is the correct size.