Elementary chemical microscopy elementarychemi00cham Year: 1921 OBJECTIVES AND OCULARS Fig. i. Zeiss Variable Objective. low powers, the chemist will find an objective of this sort an exceedingly great convenience. Fig. i shows a variable objec- tive as manufactured by Zeiss. Its range of magnification lies between 29 and 43 diameters and its free working distance between the limits 53 millimeters and 13 millimeters. To obtain a similar range with non-variable objectives requires four or five. Variable objectives do satisfactory work and are relatively A measure of the quali
Elementary chemical microscopy elementarychemi00cham Year: 1921 OBJECTIVES AND OCULARS Fig. i. Zeiss Variable Objective. low powers, the chemist will find an objective of this sort an exceedingly great convenience. Fig. i shows a variable objec- tive as manufactured by Zeiss. Its range of magnification lies between 29 and 43 diameters and its free working distance between the limits 53 millimeters and 13 millimeters. To obtain a similar range with non-variable objectives requires four or five. Variable objectives do satisfactory work and are relatively A measure of the quality of an objective lies in its ability to make clear any fine and delicate details of structure. It is, therefore, customary to speak of the resolv- ing power of objectives and express this attribute in terms of the number of fine lines per unit length the different objectives will render distinctly visible, or, in other words, the resolving power of an objective can be defined as the minimum distance apart two lines or spots may be and yet appear as two distinct individuals. The resolving power of an objective is dependent upon its light-collecting and light-transmitting power; this in turn is governed by the numerical aperture and by the particular wave-length of light entering the lens system. In general it may be stated that in properly corrected objec- tives the resolving power is directly proportional to the numer- ical aperture. This is based upon the assumption that the illuminating cone of light completely fills the aperture of the objective. In the case of ordinary objectives we find that, theoretically, the limit of resolution will be attained when the magnification of an objective reaches about 900 when using white light. The chemist is not alone interested in the brightness of the image and in the resolving power of an objective, but he is vitally concerned with another property, namely, the ability of the 1 An excellent variable objective of great penetrating powe
Size: 1173px × 1705px
Photo credit: © Bookend / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: archive, book, drawing, historical, history, illustration, image, page, picture, print, reference, vintage
