Lenslok is a copy protection

Copy protection

Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...

 mechanism found in some computer games and other software on the 8bit Atari

Atari 8-bit family

The Atari 8-bit family is a series of 8-bit home computers manufactured from 1979 to 1992. All are based on the MOS Technology 6502 CPU and were the first home computers designed with custom coprocessor chips...

, Commodore 64

Commodore 64

The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...

, Sinclair ZX Spectrum

ZX Spectrum

The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research Ltd...

, Sinclair QL

Sinclair QL

The Sinclair QL , was a personal computer launched by Sinclair Research in 1984, as the successor to the Sinclair ZX Spectrum...

, MSX

MSX

MSX was the name of a standardized home computer architecture in the 1980s conceived by Kazuhiko Nishi, then Vice-president at Microsoft Japan and Director at ASCII Corporation...

 and Amstrad CPC

Amstrad CPC

The Amstrad CPC is a series of 8-bit home computers produced by Amstrad between 1984 and 1990. It was designed to compete in the mid-1980s home computer market dominated by the Commodore 64 and the Sinclair ZX Spectrum, where it successfully established itself primarily in the United Kingdom,...

. The most famous game to use it was Elite for the ZX Spectrum.

The Lenslok device was essentially a row of prism

Prism (optics)

In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...

s arranged vertically in a plastic holder. Before the game started, a two-letter code was displayed on the screen, but it was corrupted by being split into vertical bands which were then rearranged on screen. By viewing these bands through the Lenslok they were restored to their correct order and the code could be read and entered allowing access to the game. The device was small enough when folded flat to fit next to an audio cassette in a standard case.

In order for the Lenslok to work correctly the displayed image has to be the correct size. This meant that before each use the software needed to be calibrated to take account of the size of the display. Users found this setup particularly annoying, at least in part due to the poor instructions that were initially shipped. Additionally, the device could not be calibrated at all for very large and very small televisions, and some games shipped with mismatched Lensloks that prevented the code from being correctly descrambled. The Lenslok system was not used in later releases of Elite.

Software that used the Lenslok system:

• Elite, released by Firebird
• OCP Art Studio, released by Rainbird
  Rainbird
  Rainbird, Rain Bird or Rainbirds may refer to:- Birds :* Rainbird, colloquial name given to various birds thought to sing before rain, including the European Green Woodpecker, Jamaican Lizard Cuckoo, Pacific Koel, Channel-billed Cuckoo, Burchell's Coucal and Black-faced Cuckoo-shrike, as well as...
  
  
• Fighter Pilot, released by Digital Integration
• Tomahawk, released by Digital Integration
• TT Racer, released by Digital Integration
• Jewels of Darkness
  Jewels of Darkness
  Jewels of Darkness is a trilogy of text adventure games by Level 9. The individual games were initially released separately in 1983. They featured some themes inspired by the books of J. R. R...
  
  , released by Level 9 Computing
  Level 9 Computing
  Level 9 was a British computer text adventure game company which produced some of the most advanced games of the 1980s. Founded in 1981 by Mike Austin, Nicholas Austin and Pete Austin, the company produced about 20 games for BBC Micro, Nascom, ZX Spectrum, Commodore 64, Oric, Atari, Lynx 48k, RML...
  
  
• The Price of Magik, released by Level 9 Computing
• ACE, released by Cascade Games Ltd
• Graphic Adventure Creator
  Graphic Adventure Creator
  Graphic Adventure Creator is a game creation system/programming language for adventure games published by Incentive Software, originally written on the Amstrad CPC by Sean Ellis, and then ported to other platforms by, amongst others, Brendan Kelly , Dave Kirby and "The Kid"...
  
  , released by Incentive Software
  Incentive Software
  Incentive Software Ltd. was a British video game developer and publisher founded by Ian Andrew in 1983. Programmers included Sean Ellis, Stephen Northcott and Ian's brother Chris Andrew. Later games were based around the company's Freescape rendering engine...
  
  
• Moon Cresta
  Moon Cresta
  is an arcade game released in 1980 by Nichibutsu. Incentive Software published a version of this arcade game for many 8-bit home computers of the time. Dempa also released a port of both Moon Cresta and Terra Cresta for the X68000...
  
  , released by Incentive Software
  Incentive Software
  Incentive Software Ltd. was a British video game developer and publisher founded by Ian Andrew in 1983. Programmers included Sean Ellis, Stephen Northcott and Ian's brother Chris Andrew. Later games were based around the company's Freescape rendering engine...
  
  
• Supercharge, released by Digital Precision