52mm is the thread size on the front of some EOS lenses, the back side
is a special mount. Inside are aperture/iris & autofocus mechanisms. The
closeup lens is like a simple coke bottle with threads so you could put
that on the end of an EOS lens.

It is possible to reverse an EOS lens on your powershot for doing macros
but the magnification may or may not be useable depending on the lens.
In fact that probably won't work, normally you put a short lens reversed
on a longer lens & the powershot is inherently short at any zoom range.
I have an old slide projector lens, quite small that can be held to the
front of my P&S digital that does great magnification but it vignettes
as a circle in a black background:
<http://www.edgehill.net/1/?SC=go.php&DIR=California/Bay-Area/San-Francisco/our-g
arden/other&PG=1&PIC=3>
-the following picture is without the lens attached
-the lens almost scrapes against the subject it's so close