Pentax MG w/ 50mm, f1.7 lens. I paid $4.95 for it a local thrift store. It's missing the wind lever cover, but it works perfectly.
I think I have lenses for that camera. Is it an M42 mount?
No, it's a Pentax K Mount. You can use your M42 lenses on a mirrorless digital camera like the Sony NEX/A bodies. The photo of the Pentax MG was taken with my Sony NEX-5N and a Yashinon 50mm, f1.7 lens - very similar to the Pentax 50mm on the MG in the photo.
I've been thinking of getting a 10 stop Neutral Density filter to try for some photos like yours. I found out something I think is really cool about taking them in raw. If you shoot in raw, you can shoot the photo using the camera's (Nikon D7100 in my case) black and white mode so that you see the result as black and white on the camera. Because it is shot in raw, all the colour infomation is captured in the file too. Since my camera takes two SD cards, I am going to get another card for jpg copies to be written to card slot two too. Whoo hoo!
Which brand of adapter did you get for that Argus lens?