File:Principles of Microscope - Plate 18.jpg

English: PLATE XVIII (facing page 236).

Photographs exhibiting the impediments to microscopic resolution which are referable to diffraction and obfuscation and the improvement which is effected in the highly magnified microscopic image by the employment of Gordon's device for opening up the beam in the image plane of the objective.

Figs. A, B, C are photographs obtained by the aid of Gordon's microphotographic apparatus used in conjunction with his tandem microscope giving upon the photographic plate an actual magnification of circ. 2,500 diameters and a magnification upon the retina that would be conventionally described (vide Cap. X, subsect. 4) as a magnification of about 7,500.

Fig. A. Group of typhoid bacilli imaged by Gordon's tandem microscope employed without the ground glass screen. To be noted are the shadows and diffraction patterns of small particles of dust lying on the eye lens (vide pp. 93-94; pp. 227-228; p. 233 and p. 236). We have here the factor which is contributed by the microscope to the obfuscation and diffraction which mar the highly magnified microscopic image.

Fig. B. Photograph of the central portion of the entoptic picture depicted in Plate X, Fig. 5 (vide pp. 140-142, p. 167, p. 228, p. 233, and p. 237). This represents the factor which is contributed by the eye to the obfuscation and diffraction which mar the highly magnified microscopic image.

Fig. C. A composite photograph of Fig. A and Fig. B.

Owing to an accidental inversion of one of the plates, the right side of Fig. B is in the composite superimposed upon the left side of Fig. A.

This represents the combined contribution of the microscope and the observer's eye to the obfuscation and diffraction which mar the highly magnified microscopic image.

Fig. D. Group of typhoid bacilli imaged by Gordon's tandem microscope employed with the ground glass screen at rest. We have here the highly magnified microscopic image relieved from the blemishes (seen in C) which are referable to obfuscation and diffraction, but marred by the superimposed magnified image of the grain of the screen (vide pp. 236-237).

Fig. E. Group of typhoid bacilli imaged by Gordon's tandem microscope employed with the ground glass screen in motion. The highly magnified microscopic image has here been relieved both from the blemishes contributed by obfuscation and diffraction and from the superadded blemishes referable to the superimposition upon the picture of the magnified image of the grain of the screen.