Читать книгу A Practical Manual of the Collodion Process. Giving in Detail a Method For Producing Positive and Negative Pictures on Glass and Paper онлайн
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CAMERA TUBES AND LENSES.
If a lens gives a well defined image on the ground glass, it should do the same on the plate. Many a valuable lens has been condemned for failing in this, merely in consequence of the plate-holder not being in focus with the ground-glass. In case of deficiency in this, put a glass into the holder, lay a rule across the face, and measure the distance between them very exactly; measure the ground-glass in the same way, and make the distance agree perfectly, by moving the ground-glass either back or forward in the frame, as the case may be, so that the surface of the glass plate shall occupy precisely the same position as the face of the ground-glass when in the camera.
POSITION OF LENSES IN THE TUBE.
It is very desirable that the operator should understand the arrangement of the lenses in the tube; it not unfrequently happens, that in taking out the "glasses" to clean them, he does not return them to their proper places, and the result is that his "camera is spoiled." A couple of illustrations and a few remarks will be sufficient to enable any one to replace the lenses in them properly. ssss1 represents the tube for holding the lens, and ssss1 shows their arrangement. It will be seen that the two back lenses have a small space between them; this separation is kept by a small tube or ring of the same circumference as the lens. The two front lenses are nearest together. It will be observed that the two thick lenses are towards each other; these are made of flint glass containing much oxide of lead. The other two are double convex, and are made of crown glass. By noting the fact that the two cemented lenses go in the front of the tube, the glass having the thickest edge goes inside, and that the thickest lens of the other two goes in first, from the back of the tube, it will not be easy for the operator to make a mistake in returning the "glasses."