The User's Review: Vivitar 2X Macro-Focusing Teleconverter (with Minolta M/MD Mount), Released in 1981

These converters with different mounts for various brand cameras are specially-designed for both macro and tele shooting. Cool! Mine has a Minolta M/MD mount. As I tested, once I extended the barrel on the converter, it worked only as a macro device, and turning the barrel also did focusing besides the lens' one.

The converter comes with two covers for both ends and a case. Its original price was $79.95 as the prince tag marked on the box. For the new converters with different mounts, their prices might be close. However, my online search show that the used converter with KAR mount (with 7 pins, for both Pentax KA and Ricoh P) is more expensive since it can be easily used on Pentax DSLR with manual focusing.

The two scales in blue and white are for 50mm lens
set at the closest and infinite focus distances 

They can be used with lenses or zooms, but its manual is needed for how to convert the parameters. Therefore, I scanned the manual and posted it here.

The User's Review: Unittic Shoe Mount Light Meter

It's  a subcompact and easy-to-use shoe meter, with one turning ring on top and a zero screw at bottom. Its case is made of plastic, but the shoe is of metal.

Both Kalimar and Lafayette marketed the re-branded meters.

The User's Review: Lens Mount Ring Adapter for Using M42 Screw-Mount Lens on Pentax K Mount Body Including Digital SLR

With this kind of ring/adapter, I can use my M42 screw mount lenses/zooms on my manual focus, auto focus or  digital SLR camera bodies with Pentax K or Pentax auto focus mounts.The adapter is easy to use: 1) install the adapter first onto the body; 2) screw on the lens/zoom; and 3) to uninstall, take the lens/zoom off first and then take the adapter of.

The Pentax brand ring is more expensive than the ring by other manufactures, which often comes with an extra wrench/key for installation/un-installation of the ring.