Vivitar Auto 3X tele-converter Model 3X-1-M42 Vivitar Auto 3X-8 tele-converter-M42 I've tested these on my Spotmatic and they do seem to be working just fine. Glass is clean and clear. They're in beautiful shape and I do have the original leather cases though admittedly I am not keen on swapping or selling those with. I'd really like to keep them for other lenses when I get them. I have a real thing for these old lens containers. ;P They do have front and back caps. Otherwise they do appear to be very good tele-converters in excellent condition. I'm selling these mainly because I am trying to get an M42 telephoto/zoom lens for my Spotmatic. I need something decent for shooting birds and/or I may put whatever I get for them into an SP2. I could also maybe use some filters. Basically I'm open to offers or swaps for other M42/Pentax gear.