TK-2, Soviet teleconverter
2x, M42 mount, s/n 000045
Kharkiv plant of precise machinery "Tochpribor", Kharkiv, USSR
with box

Very good condition. Lens is clear, clean and does not have any fungus, dust or scratches. This converter had a jumping diaphragm mechanism, but it's broken - so it does not support such lenses anymore. Body has signs of age. Box is original and has sighs of age and use.

Camera "Zenit E" and lens "Helios-44-2" are not included and shown as an example only.

This is a teleconverter for cameras and lenses with M42 mount with 2x magnification. It is very simple to use - just screw it between camera and lens and lens characteristics will be doubled. "Mir-1" 2.8/37 will become 5.6/74, "Jupiter-9" 2/85 will become 4/170. On the last photo see the converter set between SLR "Zenit-E" and lens "Helios-44-2".
It has one-layered anti-reflection coating. 
Also its version TK-2M exists with jumping diaphragm mechanism that will pass exertion from the camera to lens jumping diaphragm pin.

Its price was 29 Soviet Roubles (with average salary 120 Soviet Roubles per month).

Serial number - 000045
Type of thread - M42 mount
Dimensions (mm): 48*48*37
Magnification - 2x
Mass - 112 g (139 g with box)
One-layered anti-reflection coating