"I have the distinction of having filmed using Duplex a few years ago. The late John Cunningham made the filmstock from 16mm - he also processed it after some filming.  I showed the resultant 100ft at Wimborne and later did a talk and demo at Pimlico.  It doesn't look very widescreen, but picture quality wasn't bad (and that was with ex-govt B/W stock).  It is virtually impossible to edit, splice or even rewind, as it immediately springs into tiny coils.  I had to stick the film down either side of the viewer and the same for splicing.  (I was able to use a normal 9.5mm editor/viewer, just masking the image to cut the stray light. The CIR splicer worked OK - can't remember but I must have had to cut off surplus tape after joining.)  The projector is very complicated junk - the bits that look like sprockets are just plain wheels - one is locked - obviously the drive to it didn't work properly.  Amazingly it does form film loops, but the fixed plain wheel must scratch the film.  It also has a 500 watt lamp, so if the film sticks it immediately melts!  I did fit a QI lamp in the classic-only Monaco but haven't bothered with the Duplex/Monoplex/Classic model I have now.  It is just a weird novelty I suppose.  When changing the Monaco from Duplex to Classic (or vice versa), if the various items aren't carried out in the correct order the claws get damaged or broken off. The instruction book has pages of details on the change-over. Most of the Monaco’s were stripped, the Duplex bits removed, one lens mount blanked and then sold off at £45 around 1960 - 1964.  Not sure if the very few punters in the UK (less than 60 I think) had a refund or their equipment converted to classic 9.5mm.  I think the Duplex film stock (although not listed) was available to order in France up to the late 1950s.

I remember a camera shop in Chichester had the Duplex system on display (1957 I guess?).  Doubt it they sold any kit though - at around £80 for the camera and the same for the projector it was rather expensive.

At least the attractive 'Lido' came out of the fiasco.  It is rumoured that the idea for double run 9.5mm came out of a boozy dinner in Paris when a Kodak (well Kodak-Pathé in France) bod drinking with Pathé-Baby (well SCI Pathé by then) made a crack about 9.5mm double-run.  The Pathé people went home and decided to have a go!!   

 The other promised camera and projector models were never made as far as I know and the few 'H' cameras converted in the UK were put back to Classic and sold in the usual way.    Ken Valentine mentioned that they can be spotted by extra rivet holes blocked on the inside of the door I think.  I actually probably still have a couple of the 'H' viewfinder Duplex glasses in my spares boxes.  Have seen, but don't have, the double ended 'H' chargers intended for Duplex.  There was also a Marguet splicer made - never seen one though.

I have an Australian colour Duplex brochure which shows the crappy Pathé Mirage on its side for duplex, but no French collectors remember seeing a duplex Mirage, so probably just another of the Pathé sales manager's dreams.

The cost of the Duplex launch in the UK was the finish for Pathescope financially - in 1956 or 1957 they had to lay off about 60 staff and farm out assembly and repairs to the ex-workshop manager John Foster.  I guess it was the cost of the large advertising campaign (whole page adverts in ACW and subsidised dealer ads in newspapers and magazines)   Some say the French parent company insisted on this, but I can't believe that as there was far less Duplex advertising in France!  In any case, the UK end was really only a franchise and could choose what they imported.  Duplex probably also created the final split with France, Pathescope then buying 9.5mm Ferrania colour film stock, for example, which no doubt was against the rules of the franchise."