Section view of patt 23

Dedicated to the worlds most famous stage spotlight, the Strand Patt 23

Designed by aircraft designer Morgan McLeod (along with many other strands lanterns of the period) with Frederick Bentham doing the technical specification, and introduced in 1953, the Strand Pattern 23 was the first mass-produces spotlight. Unlike its predecessors which were primarily constructed from sheet metal the Pattern 23's body was manufactured from aluminium, using high pressure die-casting.

Strands 'Baby Spot' the Pattern 23, and its companion the Pattern 123 fresnel, revolutionised stage lighting, using optics and reflector technology which provided over twice the light output of any similar wattage spot of the day. [ The Pattern 23 was the ETC Source Four of its day ]

Initially produced in batches of 5000, production ran until 1983, when it was replaced by the Strand Minim23

Over its 30 year production run more than 500,000 were produced in several variations, details of these are provided below

Strand Pattern 23 ( Patt 23 ) Mk1

Patt23. Mk1

1953 - no shutters - slot in masks are used to shape the beam

Ventilated die-cast aluminium body and lens tube assembly designed with medium prefocus lampholder for the alternative lamps listed below. Body is hinged at the rear to give access for lamping and cleaning. Rear part carries a 7-in. diameter super pure anodised reflector and the front half a 7-in. diameter annular spherical reflector to collect light which would otherwise be masked off and wasted. The light is directed onto a gate for diaphragm masks which are focussed hard or soft by an adjustable 3-in. diameter, 5-in. focus p.c. lens in tube retained by safety chain. Four diaphragm masks with circular holes supplied as standard. Front of lens tube has runners for and is supplied with one metal colour frame. The cast fork with clamping disc and three-eighths of an inch Whitworth threaded hole is fitted with a -in. diameter plain stem, allowing lantern to be mounted on a stand. Stem can be unscrewed and replaced by any three-eighths inch Whitworth bolt for fixing to standard L clamps and other suspensions. Wired with 3 ft. heat-resisting tails and stoved crystalline black outside, matt black inside. Lamps : 250-watt Class B.1 round bulb projector, 500-watt Class A.1 tubular projector*, or preferably 500 watt Class T projector, all with medium prefocus caps.
*Only to be used cap down and only tilted within 22 of the vertical.

DOWNLOAD : The 1967 datasheet   covering the Patt 23, 23F & 23W

Pattern 23s ( Patt 23s ) Mk1 section

The standard components of the Mk1 Pattern 23, shown in the cross sectional diagram, are :-

1) Runners for colour medium frame.
2) Front drawer tube containing one lens only on a standard lantern.
3) Second lens added for wide angle spotlight. (Patt23W)
4) Gate for shutters or iris diaphragm
5) Die cast aluminium housing
6) Frontal reflector
7) Rear reflector
8) Rear door for re-lamping, cleaning etc
9) Door handle
10) Prefocus lamp holder (for P28s type lamps)
11) Light intensifying knob
12) Safety chain for front lens draw tube

The standard beam angle of a Pattern 23 is 22 degrees. Where a different beam angle was required, this was achieved by changing the standard lens.

Pattern 23f ( Patt 23f ) Fresnel lens


Fresnel lens, providing a diffused edge to the beam

When the standard lens (2) on the Pattern 23 is replaced with the Fresnel alternative a beam angle of 30 degrees can be achieved. The beam is also diffused and sharp focus is no longer possible. The Patt23F option is less suitable for pattern projection.

Pattern 23s ( Patt 23s ) Mk1 with built in shutters


Narrow angle lens tube

When the standard lens (2) on the Pattern 23 is replaced with the narrow angle lens tube a beam angle of 11 degrees can be achieved. The narrow angle lens tube replaces the standard 3.5in lens with a 6in diameter objective lens.

DOWNLOAD : The 1967 datasheet   for the Patt 23N


Wide angle lens option

By adding an additional 3.5in objective lens in the rear position of the standard lens tube a wide angle of 37 degrees can be achieved. When this lens is installed the lens tube diaphragm should be replaced.

The three options listed above could be ordered as a factory option, or an existing Pattern 23 can be modified by adding the appropriate lens options.

Patt23 /H /R

Rear handle option (factory fitted only)
Pattern 23 as a followspot

The Pattern 23 could be ordered with a heat resistant rear handle installed, allowing it to used as a basic followspot by adding the /H suffix.

When a Pattern 23N was to be used as a followspot, the pivot point is moved using additional brackets, to counterbalance the additional weight of the narrow lens tube. Suffix /R.

This counter balance issue was resolved with the Pattern 23N Mk2

Pattern 23 fitted with rear handle

Pattern 23s ( Patt 23s ) Mk1 with built in shutters


1958 - Four built in shutters

These compact spotlghts, with four built-in but externally operated shutters, project a clear cut even beam of any profile determined by the shutters or a cut-out mask inserted in the gate runners. Four masks of fixed but different diameter are provided for circular beam shaping. Alternatively purpose-made masks (gobos) can be used for pattern projection.
Different lens combinations are available so that the most efficiant use can be made of the light collected at the gate by the front annular and the rear ellipsoidal reflectors. The Fresnel lens model, patt 23F/S, provides a diffused edge to the beam.
These spotlights are recommended for applications where quick but precice control of beam shape and spread is required as in stage and studio lighting. For the small scale stage they are ideal for the all-important lighting from the auditorium and also for side lighting close to a simple cyclorama

It should be noted that an issue with the design of the Patt23S, means that it is not possible to project a circular image at full aperture, as the shutters do not fully retract

The Pattern 23S was also available with the alternative lens options by adding the /S suffix to the appropriate order code.

23/S - Standard
23F/S - Fresnel
23W/S - Wide
note: the 23S is not offered in a 'narrow' configuration as the shutters prevent the installation of the balancing supports

DOWNLOAD : The 1967 datasheet   for the Patt 23s

Pattern 23 Mk2

Patt23 Mk2

1968/69 - Significant optical improvements. Four shutters in dedicated shutter plate.

The second generation Pattern 23 introduced in 1968 had several significant improvements over its predecessors.

The rear reflector was changed from a smooth polished surface to a faceted reflector, to remove projection of the filament shape within the beam.
The lamp adjustment knob was removed, as it became unnecessary when using a 'T-class' lamp.
A dedicated shutter plane was provided on all lens variants. To allow this a new front casting was produced. This can be identified by four nodules on the surface closest to the lamp house.

These new Mark II versions of the original die-cast spotlights all have four built-in beam shaping shutters so that the characteristics of the Profile optical system can be used to the full. Each of the four externally operated shutters can be angled through more than 90 degrees around the optical axis so that the evenly distributed beam can be accurately contained within any four or three-sided area even when projecting from an acute angle. gate runners are provided for other beam shaping accessories such as an iris diaphragm for circular beams or purpose made masks for pattern projection.

Different lens combinations, providing different maximum beam spreads, are available so that the most efficient use can be made of the light collected at the gate by the rear ellipsoidal reflector suplemented by a front annular reflector. The rear reflector is faceted to ensure an evenly distributed beam completely free of filament striation.

DOWNLOAD : The 1969 datasheet   for the Patt 23 Mk2

Pattern 23N Mk2

Patt23N Mk2

1968/69 - Significant optical improvements. Four shutters in dedicated shutter plate. Completely re-designed lens tube.

This redesigned narrow angle Profile spot uses the same inexpensive 500 or 250 watt projector lamps as the standard patt. 23 but provides more than double the intensiry.

The light is collected at the gate by a faceted ellipsoidal rear reflector supplemented by a front annular reflector. the beam is shaped at the gate either by the four built-in shutters or by the iris diaphragm. This gate aperture is focussed by a 6-inch (150 mm) diameter long focus lens into an evenly distributed, 11 degree maximum spread beam with clear cut edges.

The spotlight is equipped as a compact and inexpensive follow spot for ballrooms, cabaret clubs, etc., but is equally useful for more general stage lighting from the auditorium if the throw exceeds 30 feet ( 10 meters ).

DOWNLOAD : The 1969 datasheet   for the Patt 23N Mk2

Some fun facts

Pattern 23 sketch