Old Delft TA-7M Aerial Camera

Transcription

1 Old Delft TA-7M Aerial Camera By: Anton Hermans May, 2012 Introduction The TA-7M aerial camera was produced in Holland by the Optical Industry Old Delft specifically for the use in low flying military aircraft (F-104 Starfighter). Before this camera was introduced to the various air-forces in Europe, Old Delft had already developed a range of aerial cameras using optics that were based on Bouwers * concentric mirror design. These high altitude long focal point cameras included the TA-30 (f/ lens), the TA-60 (f/ lens), the TA-90 (f/ lens) and the TA-120 (f/6-48 lens). The TA-7M was much different from earlier Old Delft designs given the fact that this camera had to operate at low altitude and high speed. A standard short focal point Deltamar f/ (70mm) lens was used with other lens options available (e.g. f/2.7-2 ). Shutter speeds of up to 1/9000 sec. were possible given the unique focal plane shutter design. The TA-7M was not just sold as a single camera but rather as a camera system. This trimetrogon system was made up of one right, one vertical and one left looking camera. In the F-104 Starfighter the camera system was mounted inside the fuselage, just behind the nose wheel. Delivery of the TA-7M camera systems started in the early sixties and the system was eventually replaced by the Orpheus system that was introduced in the mid-seventies. This Orpheus system was developed in close cooperation between the Royal Netherlands Airforce, the Optical Industry Old Delft and Fokker VFW with the assistance of the National Aerospace Laboratory. It consisted of a pod that housed five TA-8M cameras, one infrared line scanner as well as the climate control system. The Orpheus pod was mounted on the aircraft s centerline rack (Dutch air-force: first F-104 and later F-16 aircraft). The TA-8M cameras were almost identical to the TA-7M cameras. *Prof. Dr. Bouwers (President of N.V. Optische Industrie De Oude Delft from 1941 to 1963)

2 TA-7M camera system The main components of the TA-7M system included 3 cameras (body, magazine, lens and yellow filter), 1 speed control box, 1 rate selector / camera control panel and 1 position signal converter (Lockheed). First series: TA-7M camera, 70 mm lens, 52 mm lens, filter and speed control box Camera Specifications Use all weather reconnaissance at low altitudes Means of operation electric, remote control Film 70 mm perforated, 100 ft standard base or 150 ft thin base Film transport continuous, 14 perforations per cycle Image size 2½ x 2½ No. of exposures per film standard base 450, thin base 650 Shutter focal plane, rotating disc Shutter times 1/9000, 1/5400, 1/2400, 1/1500 and 1/900 (+/- 10%) sec Data latitude (3 digits), longitude (3 digits) frame number (3 digits) written data Iris diaphragm automatic: max. aperture: lens 70mm f/1.6, lens 52mm f/2.7 automatic: min. aperture: lens 70mm f/20, lens 52mm f/22 ASA settings 100, 200, 400, 800 or 1600 ASA Temperature range -51 C to +71 C (-60 F to +180 F Vibration 10 g in any direction Humidity 5 to 100% RH Lenses Deltamar f/ mm = g with yellow filter Deltamar f/ mm = g with yellow filter Electrical data a) 28 VDC (23 29 V), current starting peak 9.5A b) 115 VAC, 400 cps, 1A Weight camera 3,640 g magazine 2,145 g (loaded)

3 Camera design -Focal plane shutter A patent application covering the focal plane shutter design used for the TA-7M camera was filed by Old Delft in The actual patent was obtained in 1963 (e.g. US patent no. 3,114,306, UK patent no. 1,004,421 and German patent 1,183,777). For the high shutter speeds (less than 1/1000 sec) that were required, between- the-lens and flexible curtain shutters were found to be unsuitable due to the resulting high accelerations and stresses. The Old Delft focal plane shutter design eliminated this problem by using two continuously rotating discs whereby one disc is rotating faster than the other one. The first disc has a higher rotational speed compared to the second disc. As a result, the slit in the first disc is covered 8 times per 9 revolutions and only once per 9 revolutions is the film exposed. Although it has the drawback of occupying more space than flexible curtain shutters, the rotary disc shutter offers considerable advantages: - Exactly the same shutter speed for all parts of the image plane - Possibility of realizing short to very short exposure times - Great shutter efficiency averting any perceptible motional un-sharpness - Very reliable with minimal wear and tear due to low acceleration and stresses on parts

4 -Motion blur The TA-7M main motor is driving the shutter discs and is also responsible for transporting the film. The ratio between shutter speed and film speed is fixed. Exposing the film is achieved by engaging the electric clutch between main drive and film transport. The film moves continuously during operation and thereby provides a high degree of image motion compensation at high speed, low altitude flights. Inherently this makes the TA-7M camera unsuitable for reconnaissance at higher altitudes. -Aperture control A patent application covering part of the automatic aperture control that was used in the TA-7M camera was filed by Old Delft in The actual patent was obtained in 1966 (e.g. US patent no. 3,245,331). Automatic aperture control was already available in the 1950s but what made the Old Delft design unique was that the illumination of the focal plane was continuously measured through the lens (TTL). Reflective white coating on front disc Front disc with 17 opening Rear disc with 5.4 opening (this is the actual shutter disc) Light passing through the lens is diffused by a reflective coating on the shutter disc and is then measured by a photo-resistor that is mounted in such a position that it does not obstruct the light path between the lens and the focal plane. The TA-7M was already the fastest aerial camera at the time it was introduced but was most likely also the first camera to have an automatic aperture control system using TTL light-metering.

5 -Data recording The space between exposures is used for data recording. The data recordings include frame number, geographic position and written text. Exposing the data on film is achieved by a xenon gas filled flash lamp inside the camera. counter assembly frame number longitudinal & lateral displacement data stick for written text The longitudinal and lateral displacements are visualized by 2 sets of 3 digit counters that are driven by stepping motors. One full rotation of the first counter disc corresponds to a displacement of 1/10 or 6 nautical miles.

6 Optics The TA-7M optics were designed and produced by Old Delft. A wide variety of lenses was made available and included: Lens type (Deltamar) 38/2.8 52/2.7 64/1.8 70/1.6 75/ / / /2.8 Focal length Relative aperture f/2.8 f/2.7 f/1.8 f/1.6 f/1.7 f/1.1 f/2.8 f/2.8 Field of view 74 x x x x x x x x 15 Approximate resolution (lps/mm) (from left to right: TA-7M with Deltamar f/1.6-70mm, f/1.8-64mm and TA-8M with f/ mm) Speed control box The speed control box is housing 3 (1 for each camera) electronic amplifiers that control the speed of the main camera motor. The servo-systems for the main motors of the cameras are independent of each other. Each system contains the following elements: The main motor with tachogenerator (inside the camera body) that measures the number of revolutions by supplying a corresponding voltage. Part of this voltage is compared, through a potentiometer in the rate selector, with a reference voltage. The difference is fed to the main motor supply, through an electronic amplifier in the speed control box.

7 Rate selector / control panel The very first systems were supplied with cockpit mounted rate selectors as shown in the picture (left side). Later systems used more sophisticated control panels enabling the pilot to control the cameras separately as well as monitor their film consumption. Modifications to the system included feeding the V/H signal directly to the speed control box thereby eliminating the need to manually (calculate and) set the shutter speeds. Position signal converter An inertial navigation system (INS) determines the position of an aircraft by continuously processing the signals coming from its instruments. An aircraft carrying such an INS therefore does not depend on radio communications / beacons. The (LN-3) inertial navigation system that was used in the F-104 Starfighter was developed by Litton in the 1960s and the Starfighter was the first super-sonic fighter aircraft to be fitted with this system. The LN-3 platform used two G200 gyroscopes and three accelerometers. The position signal converter that was used with the TA-7M camera system was produced by Lockheed and converted the signals coming from the aircraft s inertial navigation system to signals driving the two counter stepping motors in each camera (see data recording).

8 Operation The TA-7M camera system functions almost completely automattically. Only the exposure frequency has to be set in the cockpit (later this was changed to automatic operation see test and evaluation). The correct shutter speed is calculated using the V/H nomogram shown below. Corresponding shutter speeds Frames/ sec shutter speed 1.5 1/ / / / / /9000 Old Delft s circular slide rule to determine correct shutter speed

9 The operation of the system is divided into 3 stages: a. rest position, in which only the latitude and longitude coordinates follow the position of the aircraft. b. stand-by, in which case the main camera motor is running, the shutter discs are rotating and the diaphragm control functions. c. operation, (F activated by the gun trigger) in which case the film is transported and periodically exposed and the incorporated frame counter functions; the data recording lamp flashes and the data are recorded between the exposed frames. Complete system as used in the RF-104 Starfighter With the exception of the camera control panel, all parts were assembled on the camera mounting rack. Night photography (TA-7M1) Old Delft developed a special version of the TA-7M suitable for night photography. This version received the designation number TA-7M1 and could be used for vertical photography at altitudes between 240 and 750 meter using an f/ mm lens. The TA7M1 camera was fitted with a flash contact and used shutter speeds between 0.3 to 3 frames per second. The capacity of the electronic flash unit used with the TA-7M1 approximated 40,000 candelasecond with a maximum flash rate of 2 flashes per second. At an altitude of 750 meter the camera covered a land strip with a width of 420 meter and one film load (30 meter film) could photograph a 200 km long strip. The resolution at this altitude corresponded to approximately 20 cm.

10 Documentation A comprehensive set of manuals was made available to the TA-7M camera system operators. OVERHAUL OPERATION AND SERVICE INSTRUCTIONS ILLUSTRATED PARTS BREAKDOWN System components covered by these manuals included the speed control box (O.D. part no. 34R), rate selector (O.D. part no. 34S), camera body (O.D. part no. 34T), film magazine (O.D. part no. 34U) and objective (O.D. part no. 36A&B). Early test and evaluation The TA-7M camera was tested and evaluated in 1963 by the U.S. Naval Air Development Center (Johnsville, Pennsylvania / Report no. NADC-AP Dec 1963). The following extracts of the test report are most significant: -It would be desirable to operate such a camera in conjunction with the existing camera control systems, rather than the Delft V/H manual computer. With the NCCS-4 system, the ground speed and altitude are determined by electronic sensors and fed into a computer which in turn feeds the proper pulses to the camera for control of the forward motion compensation and camera cycling rate. Inasmuch as the IMC and cycling rate in this camera is not continuously variable, but is limited to six discreet steps, it would require additional electronic equipment to make the TA-7M camera compatible with the NCCS-4 system. Note: The early manual camera control was upgraded to automatic speed control. Whether this report initiated this modification is unclear. -It is concluded that the TA-7M camera is a very specialized camera for low altitude high speed operation only. As such, it has a superior capability, because of its high recycling rate and high shutter speeds, than any other similar reconnaissance camera. There were no malfunctions during the limited test program conducted on this camera in which there were only six flights. It could be predicted however, that this camera would have a high life expectancy, and require little maintenance. This is because of its simple design concept in which a constantly moving film mechanically tied to the simple rotating disc shutter eliminates the high stresses, at high recycling rates, imposed by the start and stop action of conventional cameras with between-the-lens or focal plane shutters.

11 Final test and evaluation (conducted by the author) I was able to put a TA-7M system together by purchasing components from various sources. Some parts such as the relay/fuse box and the wire harness had to be custom built. The camera bodies that I received had accumulated a lot of dirt but were left as they were. The aperture ring on the lenses was found to be sticky and it turned out that excessive grease had been used. After a simple cleaning operation the aperture rings were able to move freely. (complete set including auxiliary switching-mode power supply and relay/fuse box) The whole system was then connected and, as a first step, power was fed to the speed control box. The air blower immediately sprang to life (and produced more noise than an old vacuum cleaner). The next steps that followed included switching on the cameras one by one. To my astonishment, all cameras worked properly whereby the shutter speed could be set by the control panel and the aperture control worked automatically. The trigger/test button then engaged the film advance clutches and the counters on the control panel started ticking. Although it was clear from the beginning that the cameras consumed a lot of film at the higher speed settings, it was amazing to see this while running the system with film magazine cover removed (see picture). After decades of storage, all components still worked fine.

12

13

14

15

16

17