Diafade | the Audio Visual story


	In 1978, Diafade started production of a unique range of slide/tape dissolve systems, which were popular at the time among serious amateur photographers and with companies making training and sales programmes. Twin-projector dissolve systems mostly work by varying the brightness of the two projector lamps, so that one image fades up while the other fades down, giving a smooth transition between the two. The slide in the OFF projector is then changed, ready for the next transition. Different effects are created by varying the speed of the dissolve. The sequence is typically accompanied by a recorded voiceover and/or musical soundtrack. At a basic level, the advantage of dissolve over a sequence of slides on a single projector is that the dissolve cuts out the annoying and tiring blackout between each image. For companies, the advantages over video are the ability to choose the very best shots, perhaps from several different photographers, to update them easily, and to project big punchy images (with recent advances in technology, of course, some of these benefits no longer hold true).
	But dissolve offers so much more than that. The speed of the dissolve, the careful choice of images so that a so-called 'third image' is created as they overlap, synchronisation with an appropriate soundtrack - all combine to create a mood that sets the scene for the message of the programme. There were some mechanical alternatives in the 1970s, notably the excellent Purlock Duofade produced by Sir George Pollock, and a hefty servo-driven fader thingy designed as a special by Kodak, and used on the lecture circuit by Richard Wilson (and possibly by Alfred Gregory - can't remember). Three or four other electronic dissolve units were available, all of them 'crossfade' units - in which one lamp dimmed while the other brightened - which either used a slider to make the fade (preferred by amateurs as being more creative) or had a preset dissolve speed triggered by a pulse on the tape.
	What was different about the Diafade 2, as we christened it, was that the brightness of the two lamps could be controlled independently by two sliders. Two images could be superimposed at maximum brightness if required, but without the penalty of a 'peaky' crossfade at other times (a 'feature' of at least one competitor). Blinking, flashing and other visual effects could be freely achieved if the operator had the necessary dexterity. All the movements of the controls could be recorded on one track of a tape using a patented signal format, with a soundtrack on one or two other tracks.
	It wasn't long before we introduced the Diafade 4 - a truly unique unit providing independent control of four projectors, with slider control. With four projectors on one screen, images could be changed very rapidly to create special effects, and the old problem of waiting for the OFF projector to cycle (typically 1.5 seconds at that time) was a thing of the past.
	Programming fast sequences on four projectors in real time could be tricky, to say the least, and in response to customer demand we developed a number of one-off special controllers for the Diafade 4, out of which came a programming unit affectionately known as the 'Magic Box', which enabled all manner of looping and flashing effects to be recorded.
	This was followed by the 'Dolphin' programmer (the reason for the name is lost in the mists of time) which provided incredibly smooth and repeatable push-button dissolves up to 32 seconds duration, with automatic slide changes and various links between the projector effects. This was before the widespread availability of microprocessors, and the design and production of the equipment was a whole lot more complicated that it would be today.
	Various other specials were made, including, for example, a suitcase version of the Diafade 4, with cassette deck and audio amplifier, for a local council. The smoothness of the Diafade dissolve also caught the eye of the Science Museum in London when they were setting up exhibits in the new National Museum of Photography in Bradford, and we ended up designing and building a special dissolve system for their darkroom demonstration at Bradford.
	We also (eventually) produced an innovative twin projector dissolver called 'Diafade 1'. Intended for live lecture and business presentation users, it was a fully digital design (meaning very smooth and repeatable dissolves) which was operated with the ubiquitous Kodak Carousel hand control. The speed of each dissolve was set (0 to 16 seconds, forward or reverse) by the length of time the hand control button was pressed (in 16:1 ratio). Focus control was switched to the ON projector. Programmes could be recorded using the simple 1kHz pulse systems commonly available at the time. Very intuitive in practice. In fact so intuitive that it never caught on! A pity - we still use one here when we need to give a live presentation. By the mid-1980s the slide/tape equipment business was shrinking rapidly. The amateur market was largely saturated and few new users were coming into the fold; corporate users were moving to video and the early computer graphics. So ended an era! There's still a market today, but it's much smaller and even more specialised, and sadly we're not part of it.