I recently bought a used Soligor 2X Macro Tele-Converter. I didn't expect much but it was inexpensive, so thought I'd give it a shot. I'd read that Tele-Converters were a bad idea because you loose 2 full stops of light, and the 4 element optics in most of the cheap used ones were fairly crummy. I checked around and indeed the 7 element ones were nearly impossible to find and priced out of my "I'm just experimenting with this" range. I then discovered that some versions had removable lens sections so they could become simple extension tubes, so now I had two features to experiment with. If the 2x lens ended up being worthless at least I'd have an extension tube. When it came it took me a little bit to figure out how the take the lens tube out (it's spring loaded so push in and turn), but then I was ready to do some testing. I tried all the >50mm focal length lenses that these Tele-Converters were intended for with okay results (took a nice 1000mm equivalent focal length picture of the moon with it), but then I thought I'd try it on the 28mm Macro lens that it wasn't supposed to work at all with. Sirius Macro 28mm f2.8 at f4, 1/160 sec, ISO 200 Sirius Macro 28mm f2.8 at f4, 1/100 sec, ISO 500 with Soligor 2X Tele-Converter With Lens Inserted Sirius Macro 28mm f2.8 at f4, 1/125 sec, ISO 400 with Soligor 2X Tele-Converter As Macro Extension Tube Only I may never use this much but it does just what it's designed to do, and the results are somewhat better than I expected for a $10 investment.