No, you do not need to use an Autocal heat absorbing glass plate with the M800 Unicon condenser sets. The condenser set puts two thick glass lenses in the light path; if you use a glass plate film holder, there's a third element. Colllectively, they do this job several times over. A heat absorbing glass is recommended when you use the Setibox diffusion mixing boxes, which do not incorporate any glass elements between the light source and a glassless filmholder. Given the reflexive light path of the M800, the omission of the heat absorbing glass with a diffusion box would not be a sin for short exposures.
