The entire action is simpler than it sounds, and the temporary blurring of the image on the screen during the process of changing is supposed to give somewhat the effect of 'Dissolving Views,' and hence the name 'Dissolving Carrier.'
This appliance is three times the price of the 'Double Sliding' pattern, but the fact that it is worked from one side only is a decided advantage, though on the other hand it is not (unless great care is used) quite so silent in its action as the 'Double Sliding' type.
A further modification of this carrier adapts it to take any of the recognised 'foreign' sizes of slides, so that if a few American ones, for instance, are met with among a collection of English manufacture, there is no need to change the carrier.
There are other varieties of carriers on the market which there is no need particularly to describe, such as, for example, carriers fitted with roller curtains to give the effect of a curtain rolling up, magazine carriers to hold twenty-four or more slides and exhibit them in rotation, and other patterns too numerous to mention. Of these the reader must be left to judge for himself, but, generally speaking, simplicity in a carrier is the most important point to be looked for, and complications, however ingenious, should be avoided.
The lantern stage must also receive consideration, but it will be better to discuss it as part of the mechanical construction of the lantern.
The Objective is really the most vital part of a lantern, as the definition of the picture almost entirely depends upon the excellence or otherwise of this lens. This will be obvious at once when it is realised that the objective has to project on to the distant screen a greatly magnified image of the comparatively small lantern slide, and the intending purchaser is strongly advised to economise almost anywhere rather than on this item.
The action of a lens in focussing the image is perhaps best explained by a simple diagram (Fig. 39), from which it will be seen that all the rays proceeding from any one point on the object are re-converged (when the lens is in focus) to a definite point on the image, and the perfection of the picture depends upon the lens performing this function accurately.