—— 20 F3) 2 | United States Department of the Interior GEOLOGICAL SURVEY RESTON, VIRGINIA 22092 526 National Center May 3, 1978 Mr. Michael Goldsmith Select Committee on Assassinations U.S. House of Representatives 3331 House Office Building, Annex 2 Washington, D.C. 20515 Dear Mr. Goldsmith: Enclosed is U.S. Geological Survey Report of Calibration No. 419 covering measurements made on a 620 Imperial Reflex Camera, Commission Exhibit No. 750. These measurements have been made in accordance with instructions contained in your letter of March 2, 1978. The fee for this work is $320. You will be billed for this amount at a later date by our Finance Office. Sincerely yours, hth Ebb) Roy R. Mullen Chief, Branch of Research and Technical Standards Enclosure HW 46106 DoclId:32270041 Page 3 . ce - —_- ~
USGS Report No. RT-R/419 United States Department of the Interior GEOLOGICAL SURVEY RESTON, VIRGINIA 22092 REPORT OF CALIBRATION May 5, 1978 of 2 1/4 X 2 1/4 Camera Camera type 620 Imperial Reflex Camera Commission Lens type DUO Identification Exhibit No. 750 Nominal focal length 77 mm Maximum aperture £/4.5 Test aperture £74.5 Submitted by Select Committee on Assassinations U.S. House of Representatives Reference: Letter dated March 2, 1978 from Mr. Michael Goldsmith These measurements were made on Kodak Verichrome Pan film type 620 ’ developed in D-19 at 68° F for 3 minutes with continuous agitation. This film was exposed on a multicollimator camera calibrator using a white light source rated at approximately 3500K. I. Equivalent Focal Length: 77.55 mm This measurement is considered accurate within 0.02 mm II. Radial Distortion: D. for azimuth angle Field De angle 0 90 180 270 (degrees) 7.5 0 61 -25 -44 7 15 388 611 331 260 350 22.5 1706 ——- --- 1646 1767 The radial distortion is measured for each of 4 radii of the focal plane separated by 90° in azimuth. De is the average distortion for a given field angle. Values of distortion De are based on the equivalent focal length referred to the field angle co-tangent for 7.5°. The radial distortion is given in micrometres and indicates the radial displacement of the image from its distortion free position. A positive value indicates a displacement away from the center of the field. These measurements are considered accurate within 10 um. It is clear from these variations in the values reported among the four radii from the average that a substantial amount of asymmetric distortion is present in this lens. HW 46108 DoclId:32270041 Page 4
an USGS Report No. RT-R/419 III. Resolving power in cycles/mm Field angle: 0° 7.5° 15° 22.5 Radial lines 14 16 20 --- Tangential lines 20 20 10 --- A A et HI ei the resolving power is obtained by photographing a series of test bars and examining the resulting image with appropriate magnification to find the spatial frequency of the finest pattern in which the bars can be counted with reasonable confidence. The series of patterns has spatial frequencies from 10 to 223 cycles/mm in a geometric series having a ratio of the 4th root of 2. Radial lines are parallel to a radius from the center of the field, and tangential lines are perpendicular to a radius. IV. Indicated Principal Point Positions of all points are referenced to the indicated principal point as origin. The diagram indicates the orientation of the referenced points when the camera is viewed from the back. The direction of film travel is to the top. Indicated Principal Point to Midsides of focal frame A Unable to Measure B 28.79 mm C 27.96 mm D 29.34 mm These measurements were made from a shadow image formed in the focal plane. The method of measuring these distances is considered accurate within 0.01 mm. The camera was aligned for calibration by autocollimating on the mounting surface where the front of the test camera-lens was placed for the film exposures. It is evident however that this is an indirect procedure, but the only method possible for a camera of this type. This alignment process made the front of the lens ring normal to the axis of the collimator bean emergent from the 0° collimator. HW 46106 Docld:32270041 Page 5 a. _ . . . ae
V. Camera Negative w! va ‘The diagram indicates thé? ° orientation, with emul'sion -: up of a negative submitted for focal frame measuréments. kant A Distances between midsides A-B 57.10 mm Cc-D 57.14 mm The method of measuring these distances is considered accurate within 0.01 mm. William P. Tayman Branch of Research and Design Topographic Division USGS Report No. RT=R/419 HW 46106 DoclId:32270041 Page 6 # } }8}§&§&~ | . . ae - . _