[old_tv_nut]

By the way, reversal processing of black and white to make slides is a usable but not high quality technique, because the negative film is designed to have a low contrast and a large overexposure latitude. This means that there is a lot of unexposed silver left in the highlights of the negative, resulting in a lot of re-exposed silver in those highlights of the reversed image - in other words, a low contrast and dark positive image. This may not have been crucial when the main goal was just to produce a recognizable projection image for a talk, but a film designed for reversal would have most of the silver exposed in the highlights, resulting in very little silver in the reversed highlights; in otherwords, a brighter and more contrasty image. This is the reason why films designed for reversal have very little overexposure latitude compared to negative films.