saw a kenko krt20 with 58 mm rear thread.... 57mm could be "tough" as 58 mm was a "standard" for a lot of camera equipment. Perhaps a step up / step down ring might help. Having said that, hopefully, you can find something that you can try and take back if it doesn't work. The reason that I say this is, my "findings" indicate that you need to position the adapt so that the image passes as close to the center as possible to avoid distortion. For projectors (most but not all but particularly those with an offset), the image comes out of the front lens element "off-center". Thus, you will need to place the adapter "off-center" a bit and hence will not be able to use the existing lens threading on the projector lens system... at least that was my "finding".