Lets toss this off quick and move on to something else… -K
The camera lucida is a sort of artistic crutch which relies on the dedication of its adherents for its success. To be sure one can enjoy incredible results with the camera lucida, but the requirements of its use coupled with the complexity and expense of the device are sufficient that for casual micrography one is better off with other methods. For the individual with the rigid dedication to acquire skill with the camera lucida it is a tool of wonderful capability, for nearly everyone else it’s a device of torture.
The principle on which the camera lucida operates is reflection. Whereas in the previous post an image of the specimen was reflected onto the drawing surface, here an image of the drawing surface is reflected into the eye as it simultaneously observes the specimen. Apparatus which achieves this has been adapted to all manner of situations and some schools of art teach the use of the camera lucida to artists as a method of perfecting perspective. For micrography the camera lucida seems to have fallen largely by the wayside, perhaps even more so than micrography in general. However, modern camera lucidas are still available and there are occasional adherients in professional and amateur microscopy who make regular use of vintage instruments.
Idealy one wishing to begin serious micrography with the camera lucida should purchase the apparatus. If however one wishes to get an idea of the use before making the expenditure a simple experiment can be made with nothing more than a coverglass. Incline the microscope so that the body is horizontal and position a coverglass at a forty-five degree angle over the eyepoint of the ocular. When aligned correctly and the specimen and area below the coverglass are illuminated just right one will see both when the eye is placed close above the coverglass.
Apparatus of this sort was manufactured for many years which consisted of little more than a coverglass (or neutral tint reflector) in a frame held to a circular fitting which would slip over the rim of the ocular. Professor Abbe improved on this design significantly (others did as well but Abbe’s apparatus is the most generally found) by replacing the simple reflector with a neutral tint reflector having a small hole in its center and cemented between two right angle prisms. Parallel with the plane of the reflector he placed a mirror which would reflect the image of the drawing surface onto the reflector. With the device over the eyepoint of the microscope ocular one could observe drawing surface and specimen as a single image while keeping the microscope inclined in the usual position.
Excepting skill, success with the camera lucida is largely a matter of alignment and lighting. Proper alignment is had by first ensuring that the position of the reflector is in the plane of the oculars eyepoint. If this condition is not met no description of the difficulty and aggravation written here will serve. Next one must position the microscope so that the drawing surface is in plane with the image provided by the eyepiece. In practice this is most easily achieved by keeping the microscope fully vertical and the drawing surface fully horizontal. If this is the case the mirror of the camera lucida may be positioned at a forty-degree angle. If one has a camera lucida with the mirror fixed at an angle other than forty-five degrees the drawing surface will have to be inclined to ensure that a ray of axial light is at a 90 degree angle with the drawing surface.
Once things are aligned lighting must be considered. Light the specimen well enough for clear vision, and the drawing surface well enough that it is not overpowered by the light of the specimen or overpowering of it in turn. The variation of the Abbe camera lucida by Bausch & Lomb pictured below bears a variable series of filters which may be turned into the path of light reflected into the eyepiece to afford some level of moderation. In practice it is often more expedient to simply reserve a variable intensity lamp for illuminating the drawing surface.
Below one can see that with the microscope fully vertical the mirror may be positioned at forty-five degrees and the drawing surface left horizontal without distortion of the drawing surface. This is not the most comfortable position for use but it is the simplest to set up. Two illuminators are visible in the photograph. That on the left is used exclusively to light the specimen and bears a frosted daylight glass and 0.3 neutral filter. The illuminator on the right is used only for lighting the drawing surface and bears a frosted daylight glass as well. The bulb in each case is a 75watt Mazda halogen spot lamp.
Looking into the camera lucida one is presented with an image of the specimen and anything that appears below the mirror. If the image of the drawing surface is too dimly lit it will be impossible to see the image of the pencil point and therefor impossible to trace the outlines of the specimen. One may find that with low powers it is often necessary to dim the light on the specimen and increase the light on the drawing surface. In the case of higher powers one will find the lighting needs reversed. With some varieties of camera lucida one must be certain to keep ones eye in the same position continuously until the micrograph is complete, otherwise the image seems to move about on the paper. With the Abbe camera lucida one may move the eye as the image can only be clearly observed when it is above the hole in the reflector.
Below is something of the image one sees while looking into the camera lucida. At the right one can see a portion of the pencil while to the left one can see the reflection of that pencil simultaneous to the image of the letter “e” slide. The lighter central portion of the image in the eyepiece is not visible in use but is caused by the borders of the hole in the reflector.
Some time I shall have to make more of my efforts with the camera lucida fit to read of. Maybe put up some of the little things it permits one to do into words, but for now the camera lucida is rather more trouble than it is worth. Without an inclined drawing table it is uncomfortable in use and provides generally inferior results as it does not encourage one to spend any time improving ones skill.