SMC Pentax-F 1.7X AF Autofocus Adapter And Teleconverter Lens, No Caps. Good Pre-owned Condition. 

This unique piece of vintage camera hardware functions as both a 1.7x teleconverter and an autofocus adapter. It was originally introduced during the early era of autofocus film cameras to bridge the gap between old and new systems.

Key Features & How It Works:

• Autofocus for Manual Lenses: Its primary selling point is the ability to turn older, manual-focus Pentax K-mount lenses into autofocusing lenses.

• Internal Glass Movement: Instead of turning the focus ring on the lens, the adapter uses the camera body's internal screw-drive autofocus motor to physically move its own internal glass elements forward and backward to achieve focus.

• Focal Length & Light Loss: It multiplies the focal length of any attached lens by 1.7x but causes a light loss of approximately 1.5 stops. For example, a 50mm f/1.4 manual lens effectively becomes an 85mm f/2.4 autofocus lens. 

• Compatibility: It is highly sought after by collectors and Pentax DSLR shooters because it still functions perfectly on modern Pentax digital bodies that retain the mechanical screw-drive AF coupling.