Olympus OM system close-up and macro equipment

Introduction

This is one of the original set of 3 bellows macro lenses for the Olympus OM system and was first produced in 1972. Unlike nearly all of the other OM lenses, this one has a click-stop manual diaphragm instead of an automatic one, and so exposure has to be measured withe lens stopped down. Focusing is easier with the aperture wide open. Like the other 2 manual macro lenses, the aperture scale appears upside down when viewed from behind the camera. This is because this lens was expected to be used pointing downwards on a copy stand or a macro stand, so that the scale appears right way up when viewed from the front.

This macro lens is designed for magnifications from 4× to 12× and so it is appropriate for objects ranging from 6×9 mm down to 2×3 mm.

The Zuiko Macro 20mm f/3.5 lens is intended for use with the Auto Bellows, although it can also be used with the Telescopic Auto Tube 65–116 that was introduced in 1980. It can also be used with extension tubes, but with fixed magnifications.

The Zuiko Macro 20mm has a small screw thread mount (RMS – Royal Microscopical Society – thread, 0.8″ diameter, 36 t.p.i.), the same as microscope objectives, and requires an Objective Lens Mount PM-MTob to convert it to the OM bayonet fitting.

This lens pre-dates the macro flash units, and so does not have a filter mount for attaching them. However, it is possible to use strong glue to fix an empty 49mm filter mount to the front of the PM-MTob adapter.

In 197?, this lens was discontinued and replaced by the Zuiko Auto-Macro 20mm f/2 lens, which is faster, has an automatic diaphragm, has a standard OM bayonet instead of the RMS screw thread, has helicoid fine focusing, and has a 49mm filter mount for attaching the macro flash units.

Versions

1.  ZUIKO MACRO f=20mm 1:3.5  (single coated) (200xxx)
2.  ZUIKO MACRO 1:3.5 f=20mm  (single coated) (200xxx, 201xxx)
3.  ZUIKO MC MACRO 1:3.5 f=20mm  (multicoated) (202xxx, 203xxx, 300xxx)
4.  ZUIKO MACRO 1:3.5 f=20mm  (multicoated) (300xxx)
5.  ZUIKO MACRO 20mm 1:3.5  (multicoated) (301xxx)

Features

Optimum range ×4 – ×12 Working distance 18–21 mm Lens elements 4 Lens groups 3 Lens coating Early versions single coated Late versions multicoated Iris diaphragm Manual (click stops) Iris blades 8 Maximum aperture f/3.5 Minimum aperture f/16 Focusing helicoid None Length 20 mm, 0.8 in Maximum diameter 26 mm, 1 in Weight 50 g, 1.8 oz Mount RMS screw thread (0.8″ diameter, 36 t.p.i.) Adapter (required) Objective Lens Mount PM-MTob Focusing screens 1-11, 1-12 Front cap None Rear cap None (lens screws into case) Case Hard plastic (same as 38 mm f/3.5 macro) Hood None Filter size 21 mm (slide-on) US catalog no. 103-700 Introduced 1972 Discontinued

Zuiko Macro Lens 20 mm f/3.5 on PM-MTob adapter Cross-section Plastic case

Magnification range with Auto Bellows

Lowest magnification	×4.3	Subject area	8.4×5.6 mm	Working distance	21 mm
Highest magnification	×12.4	Subject area	2.9×1.9 mm	Working distance	18 mm

Magnification range with Telescopic Auto Tube 65–116

Lowest magnification	×?	Subject area	?×? mm	Working distance	? mm
Highest magnification	×?	Subject area	?×? mm	Working distance	? mm

Accessories

The Objective Lens Mount PM-MTob is required in order to mount the lens on the Auto Bellows. A Lieberkühn Reflector and a Mirror Housing were made to fit this lens.

See also:    Close-up and Macro Photography – Bellows Macro Lenses

Send comments or questions to Alan Wood

   
Created 18th May 2001   —   Updated 17th June 2008
Copyright © 2001–2008 Alan Wood