Tamron have made a 90mm macro for years in various mounts and it has rightly attained legendary status. I have a newer f.2.8 (older ones were f2.5) and it is outrageously good. It's no portrait lens - resolves far too much detail and is quite harsh (and not quite fast enough) but it's the most outstanding macro lens...
Close-up filters are keen, but non macro lenses are not corrected for such close distances and do not have very flat fields at those distances. But for just messing around, sure, do it.