I don't think you can get an official transparency adapter for the Canon Canoscan Lide 30 Flatbed Scanner.
I do recall a company called 'Black Widow' having an add on adapter that simply rested on top of the glass but having never tried one I can not say how good it was.
You could get a dedicated film / slide scanner for about £250 from Jessops, this has (I quote):-
48-bit, 3600 DPI optical resolution USB 2.0 Scans 35mm negs (B&W and colour) Scans 35mm slides (mounted & unmounted) Scans colour or monochrome film and mounted slides Includes Adobe Photoshop Elements 2.0
if that's bit out your price range and you like Canon products try the Canon CanoScan 3200F @ £59 from ebuyer. It has a 1200x 2400 dpi resolution and 48 bit color-depth.
I recently bought one for my uncle from Argos at about £90 which copies the slides and all negatives across beautifully...not a lot of good if you already have a scanner but worth a thought...can get you make / model details if req...
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