Adaptall 018F 1:1 extension tube for 52B/52BB 90mm macro

This is a 45mm extension tube, no optics, adaptall fitting, to accompany specifically the 90mm macros 52B/BB to achieve 1:1 reproduction.
See the 01F 2x TC listing for info on using a deglassed 01F to achieve the same thing.

A rule of thumb is that at 1:1 the effective f-stop becomes about 2 stops greater than the value set using your camera. An aperture of f/2.8 therefore becomes more like f/5.6, and f/8 more like f/16, etc. However, this rarely requires additional action by the photographer, since the camera's metering system automatically compensates for the drop in light when it calculates the exposure settings. - Cambridge in Colour.