Movie Makers (Jan-May 1928)

The focusing microscope consists of a tube A (Fig. 1) which conveniently slips inside of the view-finder tube as illustrated in Figs. 2 and 3 respectively, where it is held in place by screwing on the eye-piece B. When in position, its forward rim C is exactly in the same plane as the outer rim of the threaded receptacle in which the lens is ordinarily attached to the camera. The focusing microscope is provided with a ground glass located in the same plane as the camera film, a reversing lens midway between the ends, and the adjustable eye-piece B projecting a short distance to the rear of the camera. This eye-piece, similar to the eye-piece of an ordinary microscope, serves to magnify the image so that it appears approximately the same size as though viewed with the naked eye. Moreover, the image is seen right side up and not reversed — in other words, precisely as viewed by the eye. The eye-piece B may be adjusted to adapt it? elf to the particular eyesight of the user, so that the image will appear perfectly clear. Any lens intended to be used with the camera, regardless of its focal length, will screw into the front of the focusing microscope, which will accommodate itself to equal advantage with the usual 1-in. lens, the 2-in. lens, or any of the various tele photo lenses supplied for use with the camera. As the lens is focused on an object, the image is cast on the ground glass, where it is viewed through the eye-piece. It is thus a simple and positive means of determining when the object is in sharp focus. A most convenient attachment— although somewhat more expensive— is also illustrated in Fig. 1 and 2, consisting of a pair of matched Zeiss "Tessar" 1-in. / 2.7 lenses mounted together and focused by means of a single focusing screw D which has a Forty distance scale engraved on the rear side, where it can be readily viewed when the camera is in operation. One of the lenses E projects the image on the ground glass in the focusing microscope where it is viewed by the observer. The second lens E slides in and out of a grooved light-proof ring F, which is screwed into the threaded lens receptable of the camera. When the object is in sharp focus to the eye through the focusing microscope, it will register equally sharp on the film. There is no chance or guess work involved. If the object moves towards or away from the camera, the focusing screw D is slowly turned to the left or to the right, as the case may be, so that it may be continuously maintained in focus. A little practice makes this a simple operation. If the user has two lenses which do not happen to be "matched," they may be attached to the camera and focusing microscope respectively as illustrated in Fig. 3, which shows a Taylor-Hobson-Cooke 1-in. / 3.5 lens attached to the camera, and a TaylorHobson-Cooke 1-in. / 1.8 lens attached to the focusing microscope. The object is first brought in sharp focus to the eye through the focusing microscope, whereupon the other lens is set at the same distance marking. To use the "compensating-base" G (Fig. 2 and 3) it is attached to the camera and in turn screwed on the tripod. By moving the lever H, the camera is shifted a distance to the right or left equal to the distance between the axes of the finder tube and the lens, namely, l1/^ inch. The focusing is done while the camera is at the extreme right of the base, whereupon it is shifted to the extreme left and the object is photographed. The base finds a ready use in taking close-ups inside 5 to 6 feet of the camera, and assures the object being exactly centered on the film. Thus, in taking titles or printed matter at close range, there need be no guess work or arbitrary shifting of the object to the right. Table 3 gives the horizontal and vertical distances covered by the picture when using a 1-in. lens at ranges closer than 6 feet: A.VC*. Covtrtol "•>£ "Pictu** 1 JjtMt X>lstawM Sefctwu. 4 3 % % 1 310 '-* Hi H* •4-31 (••IS4-41 20-8 '*. I-7-3 137 10-22. 1.-12 4?t 3-a\ The foregoing figures show the necessity of accurate centering, as without the use of the compensatingbase the picture would be chopped off li/4 inches at the left and extended an even distance to the right, thus being entirely out of center at close ranges. Now let us consider some of the difficulties attendant upon the use of the so-called telqphoto lenses. In the following discussion the writer will confine his remarks to a 4-in. lens, for the dual reasons that he has found this focal length to give the most satisfactory all around results, and also because the same comments would apply to lenses of any other focal lengths recommended by the manufacturers of the camera, including the 3%-in. and the 6-in. lens. In using telephoto lenses great difficulty is experienced in obtaining proper focus when the object is closer than 50 feet to the camera. The reason for this will be apparent on referring to Table 4 and comparing the depth of focus of a 4-in. lens at any given distance with the corresponding figures for a 1-in. lens in Table 2. 3DL«iavn:« Ot>«t: M-: FSF Ft-3 F8 F II FI4 Faa lMx,. I4«.03 oo lai-S* oo 10*1? oo &3& 60 k' OO oo 41-78 OO 30-3^ 00 *°B fc 374 35-1 8E--I 34o 141 31* 1248 27-4 2s4. 227 OO I8-! 00 3»B BE 241 37r 24.1 31-1 234 ■H-l 21. 1 44-1 tto-l S7-4 i7-r l°7. IBTI OO *» 8S 43-3 17-2. 540 its 247 141 24-3 IS-I 21-1 135 3er I2-C5SS-f '*■ fc 133 111 I3| 11-5 12-1 18-3 >2-o 11-1 ll-o 234 lo-o 21-7 ■*» tz. III ni l°-1 13 3 lo-B I3-J ic~r I40 loo ISO 13 148 84 11-7 ">a fc 1-4 /o-v 1-25" lof 1 14 Jl-os s-1 11-3 81 120 t-os131 T-514-1 )|LU, 74 ir e-ss 745" 8 46" 73 8SS~ 7-oJ 47 1-1 b-3i110 4-i •MS" 44 745 4-ss 7i 445" 7-4S 4.-3 V-1 fc-o S-4 ^7 11 fa** 4.25 S--7S4-35" 4-4 s-(, t-s 6-V 5-J-S 7l fi"oS7-t 485" STI4 481 P23 4-71 J-24 4-73 5^34 4fc4 S--48 4-41 5-73 4 34 fcol 45 fa~ 34o 4 la 3-88 4-ir 384 4 >r 3-62. 4al 3.1, 4-3o 3-47 4.-U. 3.5-4 4 44 1-44 3-81 3-41 3-0,1 3.40 3-4.3 3-37 447 3-3a 3-73 3-25" 385" 314 4-oo 3t (kw 3?4 'i 34-8 37-0 3SI« 37-15 3+fl'i Slsr 34,r'i >8.( 33-8'? 311 23-1 B 4CV4 So jiw 21& 3ct 2lsr 3o-1 21-4 3og 21-2 ill 2lo 31-4 28-53 2-| 26-0 331 238 24,4 23-7 2+3 23-4 244 23-5" 2*7 234 2Fo 23 1 25:4 22-7 24o 18'-. M~ H.8S18-21 n-83 l$-2t 17-80 IS 31 17-73 l84o 17-45I8JS 17-48 18.8% 17-33 l<? 14 n-is 12-10 11-13 IA-I2 M-12 I2-IS ll-1o 12-11 M-84 I22(. II 80 1233 n-13 1254 8'S fM~ 111 8-or 1 118 8-«1 7-18 808 | 7-11 8-10 1-14 813 7-158-20 7-13 8-27 *■ Hy-pw toeoX 3) lib LKCfc TABLE 3 TABLE 4 Thus at / 4.5, with the object 6 feet distant, a 1-in. lens will have a depth of focus of 13.45 ft. (i.e. 17.1 less 3.65 ft.), as against 0.45 feet (i.e. 6.25 less 5.8 ft.) for a 4-in. lens with the same stop and distance respectively. In other words, at stop / 4.5 the depth of focus at 6 feet will be about thirty times greater with a 1-in. lens than when a 4-in. lens is used. This general fact makes it even (Continued on page 54)