An apparatus and method to represent a video signal for improved source quality versus decoding complexity for a given compression rate and improved resistance against data loss when delivered over an error-prone network. The laser beam 9a reflected by the reflection mirror 23 remotest from the deflector 23 is the laser beam for forming a yellow image. A locking dial is provided which locks the actuating sleeve against rearward movement until the dial is moved to an unlocked position. In yet another aspect, the present invention includes a relatively simple and routine synthesis of sulfinyl methyl isonitrile compounds, other isonitrile compounds and derivatives thereof.