A Camera Mount and Lntervalometer for Small Format Aerial Photography
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M. L. BENSON B. J. MYERS I. E. CRAIG W. C. L. GABRIEL A. G. SWAN Division of Forest Research CSlRO Canberra, A. C.T. 2600, Australia A Camera Mount and lntervalometer for Small Format Aerial Photography A versatile mount for two small-format aerial cameras and an electronic intervalometer suitable to trigger such cameras are described in detail. INTRODUCTION managers have developed a number of devices such ANAGERS of renewable resources have long rec- as camera mounts to meet their own requirements. M ognised the value of aerial photography and There have been many different approaches and photo-interpretation in the assessment and manage- thus many different solutions. Some of these devel- ment of those resources. In particular, large-scale opments have been reported formally, but many are aerial photographs are now an accepted medium for recorded only in internal reports, if at all. vegetation analysis. Much use has been made of This report describes two devices developed by black-and-white photography exposed in large- the Commonwealth Scientific and Industrial Re- format cameras (230 by 230 mm), although in recent search organization (CSIRO), Australia, Division of years there has been a marked swing towards the Forest Research in the course of a program of re- use of color films and small-format aerial cameras search on the application of large-scale aerial pho- (70- and 35-mm focal length). tography to forest management problems. The Color films are used because of their value in re- equipment will assist in mounting small-format cam- ABSTRACT:Scarcity of commercially available ancilliary equipment for small-format and large-scale aerial vhotogravhu has encouraged the development of specialized devicesvby users. ~~iroachYes'tothe design a& use of two'items $ equipment useful in the acquisition of small-format aerial photographs are described-a dual camera mount for 70-mm aerial photography and a camera intervalometer for small-format aerial photography. cording additional information which can be related eras internally in light aircraft for vertical photog- to botanical or ecological factors or to variation in raphy and controlling the intervals between expo- tree or stand condition caused by damaging agents. sures for a number of cameras (inter alia providing Small-format cameras are used to provide vertical a facility for sampling). aerial photography to supplement conventional pho- tography and have the advantages of versatility and low cost coupled with increased control by the user over the photographic specification. The use of supplementary aerial photography These developments have, however, posed prob- taken with small-format cameras to provide the lems for the user because there is a scarcity of com- forest manager with up-to-date information for plan- mercially available ancilliary equipment for small- ning and recording purposes is well established format photography, e.g., camera mounts and in- (Aldrich et al., 1959; Zsilinszky, 1969; Spencer, tervalometers. To meet these challenges, resource 1974). The camera mount is a critical part of the PHOTOGRAMMETRICENGINEERING AND REMOTE SENSING, 0099-1112/84/5011-1571$02.25/0 Vol. 50, No. 11, November 1984, pp. 1571-1580. O 1984 American Society of Photogrammetry PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1984 aerial photographic apparatus which can make the Most of the reported systems are rigidly mounted difference between sharp, drift-free photographs to the boom with some adjustment for camera lev- and blurred, 'crabbed' exposures. elling on the ground. One allowed for lateral or lon- Many small-format camera mounts have been de- gitudinal tilt of both cameras simultaneously in the scribed in the literature. The diversity of the de- air to counteract aircraft tilt or to allow oblique pho- signs reflects the variety of mounting situations en- tography (Rhody, 1977). Anti-vibration damping was countered by the aerial operator, the camera equip- included in one mount (Lyons, 1964). Drift-setting ment available, the type of photography required, ability is not necessary because the two cameras are and the nature of its application. The particular de- exposed simultaneously to obtain a stereo pair. sign chosen will be influenced by the following con- Cameras are inaccessible during flight. siderations: Most su~dementarvaerial vhotoera~hsare ex- posed seqGntially in flight line toUoGtain stereo- camera format-35 mm or 70 mm or other; ; camera make, shape, and attachment points; scopic coverage :ather than from a fixed base. number of cameras required; Mounts for obtaining sequential photographs may camera accessibility during flight; be either external or internal. External mounts have camera vibration damping mechanism; the advantage of not requiring modifications to the drift sight and setting requirements; aircraft and are, thus, more versatile because they make and size of aircraft; can usually be mounted on more than one aircraft. availability of suitably modified aircraft and map- Three methods of attachment which have been used ping camera mounts; and are to the window ledge, the seat rails, or the wing budget. struts. Fisher and Steever (1973) described a simple In order to put the mount which is described here metal frame mount which was hand-held out of a into perspective, the main approaches and design Cessna window. It contained four 35-mm Robot features of some other small-format mounts which cameras for multispectral photography. The most have been described in the literature will first be commonly-reported method of external attachment summarized. A simplified classification of small- is to the window ledge. Willingham (1979) used a format camera mounting systems, as they have been wooden mount for a 35-mm Canon camera. Klein described, is shown in Figure 1. (1970) included vibration damping to his window One of the most specialized types of small-format mount for a 35-mm Miranda camera. Parker and mounting system is the external mounting of two Johnson (1970) mounted a large-format camera on a cameras at a known distance apart to obtain fixed- door-clamping frame, the K-20 with a 102-by 127- base stereo photography. These cameras are usually mm format. The mount could be levelled in flight. mounted at the ends of a steel boom attached be- Meyer and Grumstrup (1978) described a sophis- neath a helicopter (Lyons, 1961; Spencer, 1979) or tocated window-ledge mount for a variety of 35-mm through a helicopter (Rhody, 1977). They have also cameras. This mount, which is now commercially been mounted at the ends of a metal frame which produced, featured a wind deflector to protect the was hand held in a helicopter (Avery, 1958) and at camera, levelling control, an aiming sight, and a the wing tips or on the wing struts of a futed-wing hinged runner to permit retraction of the camera. aircraft (Williams, 1978; Benson et al., 1984). Cam- None of these externally-mounted cameras allowed eras of 70-mm format have generally been used, compensation for drift. Mason and Matthews (1979) including Hulcher (Lyons, 1964), Hasselblad devised a versatile mount which would accommo- (Rhody, 1977; Benson et al., 1984), and Vinten date either one or two 35- or 70-mm cameras and (Spencer, 1979), but the use of an F24 camera with allow camera retrieval in flight as well as levelling 127-mm format has been reported (Lyons, 1961). and attitude adjustment. Attachment of the large mount is effected by two clamps on the window ledge and by four 127-mm heavy duty suction cups bearing against the aircraft exterior. Quite a dif- &a1 wwa mounting Mtanr ferent approach was described by CSIRO (1981) in which a Hasselblad 70-mm camera was mounted mud Mnscd alm hclkopta mounting syrtcmr mntirprvltcmr (mudbau stmo photogaphy) horizontally on the window ledge and aimed at an - external mirror to achieve the vertical view. The advantages are that the camera is not exposed to the slip-stream and it is very accessible for lens or mag- azine changes. Another a~~roachto external mounting which has A A - I been used for 35-mm cameras is to clamp a retract- SdaptcdlerscromM cammount able rod to the seat rails internally and project the camera through the open doorway (Spencer, 1974; FIG. 1. Classification of small-format aerial camera Mennis, 1978). ~hesemounts allow-in-flight lev- mounting systems. elling but no drift adjustment and the cameras are CAMERA MOUNT AND INTERVALOMETER exposed in the slip-stream. Cameras have also been and tilt, a prism viewfinder, a drift indicator, a light clamped to the wing struts of Cessna aircraft. Strut meter, and a stop watch for timing intervals be- mounts for 35-mm cameras have been described by tween exposures. Neustein and Waddell (1973) and Willett and Ward The dual camera mount which was developed by (1978), and for a 70-mm Hasselblad camera by the CSIRO Division of Forest Research falls into the Benson et al. (1984). These systems could not be last category. It is an internal mount designed to levelled in flight nor adjusted for drift. The Has- suit the camera equipment to be used and the avail- selblad mount includes a wind deflector to shield able modified aircraft. It is a robust and versatile the camera from the slip-stream. mount which suports two 70-mm Hasselblad model All of the re~ortedexternal mounting", svstems for 500 ELIM cameras or one 70-mm Vinten model 492 small-format cameras except the strut mounts have camera and one Hasselblad over two separate 150- the disadvantage of requiring an open window or mm holes in the floor of a Piper Cherokee Six air- door during flight, which can increase crew discom- craft (see Frontispiece and Figure 2). The mount fort, impair aircraft performance and handling char- allows drift correction and limited flight attitude acteristics, and increase the risk to camera and per- compensation and has efficient vibration damp- sonnel.