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I've used some 48 mm filters over a camera lens - I've done some photography with a Baader 7 nm Ha filter over a 50 mm lens.
Depending on the lens filter thread, you may be able to attach the filter using a step-down ring. However you need to be careful of vignetting, or at least accept that it may happen and crop the image.
If you are careful, you can also just stick the filter straight over the lens without the step-down ring and keep it on with some tape or something. This allows you to get the filter much closer to the lens and minimise the vignetting. With a 48 mm filter and step-down, I get a lot of vignetting on a canon 50 mm f1.4 and 28 f1.8. However carefully taping the filter on - making sure there is no actual contact between the filter and the glass of the lens, then there is no vignetting. Another way of doing it is to put the filter on the inside of the step ring, not outside, and so bring it closer to the lens.
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