Tamron 70-150mm f/3.5 (20A) - Tamron Adaptall-2 Mount

The Tamron 70-150mm f/3.5 (model 20A) is a manual-focus telephoto zoom from the Adaptall-2 series. It is notable for its constant f/3.5 maximum aperture, which provides a consistent exposure and a bright viewfinder throughout the zoom range. This lens is part of the 'Compact' series of its time, designed to be more portable than the professional SP zooms while maintaining high optical performance. Its versatile focal range is particularly well-suited for portraiture and general telephoto tasks. Check for smooth operation of the zoom and focus rings, as these should have a well-damped, professional feel. Like many lenses of this age, internal dust is common, but SDS checks specifically for haze or 'balsam separation' in the rear elements. The aperture blades should be snappy and free of oil. Ensure the Adaptall mount attaches firmly without play, as a loose connection can lead to inconsistent exposure or focus errors.