In Magic Lanterns
The optical system in Magic lanterns
was, in the early years, very crude consisting of a light source and a
single lens to focus the picture onto a distant screen. Later as an understanding
of optics in other fields was developed it was applied to the art
of projection resulting in ever sharper pictures on the screen.
The diagram illustrated below shows a later lens/light/picture configuration
The Objective Lens System
This consisted typically of 4 lenses (although the front 2 appear as one being cemented together).It is the objective lens system that is used to focus the image
The objective lens system illustrated
on the left shows more clearly the arrangement of the four lenses (marked
A,B,C and D). Lanternists frequently were required to give shows in halls
of varying sizes so a selection of objective lens systems were carried
each of a different focal length. The shorter the focal length of the objective
lens system the larger the picture would be on the screen.
Illustration on the left shows a
set of objective lenses of different focal lengths each housed in their
brass sleeves. Note the addition of the focus knob and a slot to take coloured
glass filters so the image could be modified in the projection process.
The Condenser Lens Arrangement
The condenser lens ,as its name implies, is to condense the light in an efficient way onto the slide.There appears to have been no agreed method as to which arrangement of lenses were the best and so many lanterns had wildly differing condenser lens systems as the next illustration so clearly exemplifies.
13. Plano Convex lenses
Fig. 14 Meniscus, plano convex lenses
Fig 15.Meniscus, bi convex lens
Fig 16. same arrangement as Fig.15 but with reverse sleeve mount