The Art of projection and complete magic lantern ... - Yesterday Image

t34enlarging lantern where circular condensers are used, this really beingthe cause of the unavoidable bulkiness.i-ig. 66.Condensers.—These collect the rays from the illuminant, afterwardsconvert them into a system of convergent rays, the moreconcentrated the illuminant the greater the evenness of the disc. Thefocus of the condenser should not be too long, a long focus condensernecessitates a long body, and a loss of light is also the result, or if tooshort, an equally illuminated field is not obtained, especially if a verylong focus lens is used, as the size of the condenser increases, so thefocus is proportionately lengthened.For a quarter plate negative 5)^ inch condenser is necessary, halfplate 8 inches, whole plate10}^ inches, 8 by 10 13^ inches.It is suggested in manuals on the subject, that when a large condenseris used that a third lens should be introduced between the illuminantand condenser, making it really a triplet condenser, in practice nothingis gained by this.To overcome the difficulty of the size of the condenser and thebulkiness of the body, the rectangular condensers were constructed ; bythis means the light is more equally dispersed, not mentioning the gainin illumination that usually escapes over top, bottom and sides of thenegative, when using a circular condenser there is generally a fallingaway at the corners, unless a very large condenser is used and the centrealone utilized ;owing to the great trouble of casting and grinding of theglass for these rectangular condensers, they cannot be produced quite so