Pentax's screw-mount SLR — the S3, auto-diaphragm all-mechanical body, screw mount, 1961.
The Pentax S3 of 1961 advanced the screw-mount S-series and introduced fully automatic-diaphragm operation with the lenses of its era. It was sold in the US as the H3 under Honeywell branding. It sits within the run of all-mechanical Pentax bodies that led towards the metered Spotmatic.
This is a 35mm film SLR using the screw lens mount that became the M42 standard, taking Asahi's screw-thread lenses. It has a horizontal cloth focal-plane shutter and a fixed eye-level pentaprism with an instant-return mirror. There is no built-in meter, so exposure is set manually, and the body is fully mechanical, firing without a battery. Its notable step was fully automatic-diaphragm lens operation, which kept the aperture open for viewing and stopped it down only at exposure.
The S3 suits collectors, students and photographers who want a simple, well-built screw-mount Pentax with a clear finder and smoother lens handling than earlier models. It needs a separate meter or experience for exposure, but is otherwise direct and dependable. It works well for deliberate shooting and as a route into the M42 system.
As an early-1960s body, checks matter. Inspect the cloth shutter for pinholes and even travel, testing the slow speeds for sticking. There is no meter or battery to consider. Examine the pentaprism and finder for desilvering, haze or fungus. Confirm the film advance and rewind feel smooth. A set of clean, working screw-mount lenses keeps the camera fully usable.