Originally Posted by Lowell Goudge 
The SMC-F 1.7x AF TC is an excellent teleconverter. I use it quite a bit on my SMC 300mmF4. Note that while the instructions state it must be used with lenses F2 and faster, it works very well up to F4. F4.5 is reported to work, but I have no experinece at that apature with it. I know F5.6 just does not work except in bright sunlight.
I would be careful about " close focusing claims. while the adaptor clearly will be able to focus closer than your normal 50mm lens, it will only give about a 20% reduction in close focus distance on a 50mm lens, and the longer you go with prime lenses the smaller the reduction in close focus is. that is just optics. It is not meant to replace close upl lenses or extension tubes.
But it will crop the subject by 1.7, which might be what was meant. My next project will be to see how it works with my M 100 macro. It might just give me an edge. A 170mm f/6.8 macro lens, all Pentax glass.