Submitted by Anonymous on Tue, 2011-06-07 15:39
ROYAL ASTRONOMICAL SOCIETY OF CANADA Standing Committee on Observational Activities Programme for Solar Eclipse of July 20, 1963 Bulletin No, 4 Basic Observation Programme April 6, 1963 Section B. Photographic Projects For the July 20th eclipse, we expect that the emphasis will be on photography. This bulletin gives brief descriptions of basic photographic projects. Some are comparatively simple and others are much more complex. It is hoped that members who have the equipment will undertake some of the more exacting projects. Observing groups should plan their programmes to snake the best use of the equipment available. All photographs will be of value, however, if taken with care and precision and if accompanied by a report giving complete information on method and circumstances. Once again we' stress the extreme care that must be taken to protect the eyes during the partial phases. The descriptions and instructions in these bulletins are, of necessity, very brief and there is always a danger in over-simplification. Upon re-reading Bulletin No. 3, we realized that it would have been wise to inject a word of caution about eye protection even when experimenting with diffraction gratings. * * * * * You will be interested, we are sure, in hearing how the eclipse plans of the various Centres are progressing. In Bulletin No. 2 we mentioned the tentative plans of some groups. We have now learned that le Centre de Quebec will have three field stations, each with the same programme and equipment, one station to be near Abitibi, one in the Shawinigan region and the third near the U. S. border. The Montreal Centre has decided on the location of one field station in the Grand'mere area and is still considering several sites for another station south of the St. Lawrence. In addition to its field stations, the Montreal Centre is sponsoring a special train which will leave Montreal on the Saturday morning and return that evening. Tickets will be offered first to members and then to the general public. Details will be available shortly. The Regina Astronomical Society and the Saskatoon Astronomical Society, which are closely associated with the R.A.S.C., are planning together to charter a DC-3 and fly in to the Lake Athabaska region to observe the eclipse. As you know, the National Co-ordinators rely on a contact in each Centre to keep members informed on each field of activity. However, the R.A.S.C. has many members in Canada, the United States awl other parts of the world who are not att- ached to any Centre. Therefore, a special eclipse bulletin has been sent to these unattached members inviting those who want to receive subsequent bulletins to send in their names. Every mail brings in a few more replies. To date we have heard from members in British Columbia, Ontario, Saskatchewan, California, Idaho, Indiana, Massachusetts, Michigan, Mississippi, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, Texas, West Virginia, Wisconsin, Denmark and Puerto Rico. All this keeps us very busy! Fortunately, your Eclipse Co-ordinator has a good Committee - Kenneth Chalk and Charles Good whose able assistance in planning pro- gramme and bulletins is much appreciated and Miss Ella Dack who has taken on the substantial job of mailing the bulletins. Isabel K. Williamson National Co-ordinator 1963 Eclipse 5162 Belmore Avenue, Montreal 29, Canada.
ROYAL ASTRONOMICAL SOCIETY OF CANADA Standing Committee on Observational Activities Programme for Solar Eclipse of July 20, 1963 Bulletin No. 4 Basic Observation Programme April 6, 1943 Section B. Photographic Projects In Bulletin No. 2 the more common photographic projects which can be undertaken at a solar eclipse were listed and an outline of equipment necessary for each was given. The purpose of this bulletin is to provide a more complete description of these projects. EQUIPMENT SUITABLE FOR ECLIPSE PHOTOGRAPHY The sort of work to be done determines the equipment to be: used. However, the division between partial and total phases of the eclipse suggests two major tech- niques. (1) Photography of partial phases, of Baily's Beads and the diamond ring effect. In all these cases there is a comparatively large amount of light available, Therefore, slow films, "slow" optical systems, and short exposures will be used. The camera need only have a tripod or other fixed support. Short or very short exposures will be in order. (2) Photographs taken during totality. During totality there is far less light available than during the partial phases. Comparatively long exposures are nec- essary, and photographs of the sun (prominences, corona and spectra) should probably be made with a clock-driven camera mounting to avoid blur caused by the earth's rotation. Changes in landscape illumination will likewise require fairly long exposure if they are to show much during totality. In all cases where the sun itself is to be photographed, a lens of fairly long focal length is necessary on account of the sun's (and noon's) small diameter. With short focal lengths, little detail will be visible when the photographs are subse- quently enlarged. `With 35 nun, cameras, a telephoto lens of at least 100 mm. f.l. should be used. Folding cameras, commonly of 105 or 130 mm. f.l., are also useful. (The focal length is marked on the ring which holds the lens in place.) For photography of tie prominences and for detailed pictures of the corona, it is desirable to affix the camera to a clock-driven telescope. Regarding film and exposure times, back in 1959 the Eastman Kodak Company pub- lished a booklet entitled "Solar Eclipse Photography for the Amateur" which contained a Table of Exposure Times; Unfortunately, the booklet is now out of print and as we have a very limited supply we are sending just one copy to each Centre with this bulletin. For others' on our mailing list, however, we have run off copies of the Table. Please note and make allowance for the fact that the speeds of some films have changed since the booklet was printed, notably Kodachrome. For exposures or f/ stops other than those listed, it should be noted that,as the lens opening is doubled, exposure must be divided by 4. For example, if the table gives an exposure of 1/10 sec. at f/B, then at f/l6 the exposure is 4/10 sec.: at f/4, exposure is 1/40 sec. The "f/ stop" can be found by dividing the focal length of the system used by the clear aperture of the lens. - 1 -
Eclipse Bulletin No. 4 cont'd. PHOTOGRAPHIC PROJECTS Still Photographs. 1. PARTIAL PHASES, BAILY'S BEADS, etc. For the partial phases a camera With a lens of long focal length should be used with fine-grain film and dense neutral filter. (See enclosed KODAK EXPOSURE TABLE). With the correct exposure,. the rest of the sky will remain dark on the film, If the camera to be used has a moderately wide field, say. 20 or 30 degrees, then it need not be moved for half the duration of the eclipse. If an exposure is made, say, every five minutes, then the motion of tie earth will carry the image of the sun to a new position on the film for each exposure and when printed the photograph win show the progress of the eclipse as a row of images of the sun. Done in two lots, one photograph will show the progress of the moon onto the sun's disk and the second will show its egress. Note that the sun moves 15 degrees per hour across the sky. The surface of the moon being mountainous, its outline is in some places irreg- ular and hence it is possible for some light from the intensely bright edge of the sun to shine through a Lunar valley at the rim of the lunar disk, and this gives a flood of intense light at some point or points around the rim, causing the phen- omena of Baily' s Beads and the "diamond ring" effect immediately before and after totality, Because of their short duration, the observer has to be alert to get still photographs of these effects. Note Do not attempt to record the diamond ring the corona, or both preceding following diamond ring effects, on one negative with a stationary camera. Totality is short and the images are certain to overlap. Therefore., use separate cameras or wind the film just after the beginning of totality and re-aim the camera. 2. TOTALITY (a) Corona - shape. Direct photography of the corona, although one of the simplest observations, is probably the most interesting, and it has been pointed out to us that here is a good opportunity -for the amateur to make a useful contribution. "The corona at every eclipse is different and it is important to have a record of. each one. Since the probability for cloudy weather along the 1963 eclipse path is high, it may be that amateurs distributed well along the path will be the only ones to record it In addition to long-term changes of tie corona, rapid changes in shape and position-of coronal streamers (most easily seen at minimal eclipses such as the 1963 one) have been detected at previous, eclipses. It is therefore interesting to. compare coronal ph2tographE of. the same eclipse taken at widely separated stations along the path." Photography of the corona requires that the camera have a clock-driven or guided mount. Because of the extreme range of brightness between inner and outer corona, the latter cannot be photographed well without ever-exposing the former. (See enclosed KODAK EXPOSURE TABLE.) A rotating sector shutter centred over the image in front of the film will help equalize the exposure. So will a small disk placed part way between film. and lens, but placing this will take some experiment- ing ahead of time. With an ordinary camera it is best to use film for high con- trast subjects. Best records of detail will be secured by photographing through telescope or binoculars to obtain a very long focal length. - 2 -
Eclipse Bulletin No, 4 cont'd. 2. TOTALITY (b) Corona. colour. Here again it has been pointed out that the amateur can make significant contributions. "Observations have been made at previous eclipses which indicate that the colour of the inner corona is not the same as the outer corona but the results are discordant. The usual method is to take well calibrated photo- graphs of the corona using filters of two colours (red and blue) and note intensity differences. The experiment, although simple in principle, is however a difficult one in practice since it is diffic4t to achieve the required accuracy of calibrat- ion and freedom from scattered light which may invalidate results." (c) Prominences. The prominences red, fiery tongues of light at the inner edge of the corona are sometimes very fine, sometimes missing entirely. This detail can be obtained only by photographing through telescope or binoculars. 3. SHADOW BANDS The phenomenon of the shadow bands is described in Bulletin No.3. They are very difficult to photograph on account of the low illumination and the speed of the movement. Use a short exposure time (about 1/100 second), a large aperture (f/2.0) and a high speed film (Tri-X). The camera should face downward toward a white sheet on which is placed a compass and some scale for measuring widths of the bands. As explained in Bulletin No. 3, they should be observed both before and after totality. Because of their short duration, the photographer has to be on Us alert if he hopes to take more than one exposure. 4. LANDSCAPE ILLUMINATION It is interesting to record changes in landscape illumination by selecting a subject presenting a fair range of contrast, aiming the camera and taking photo- graphs at regular intervals throughout the eclipse, say, every five minutes with one exposure at mid-totality, using a constant exposure. Exposures made at the beginning and end will probably have to be somewhat over-exposed if anything is to register during totality. 5. SPECTROSCOPIC PHOTOGRAPHY (a) Flash Spectrum. The phenomenon of the flash spectrum is described in Bulletin No. 3. It is of very short duration (about 2 seconds), and so the photographer has little margin for error in taking his shots. The flash spectrum can be photo- graphed by placing a prism or diffraction grating over the lens of an ordinary camera and timing the camera so that the spectrum enters the lens. If a prism is used, the lens should have a long Local length (about 100 mm.). Black-and-white film should be used if measurements are intended; otherwise, colour film gives interesting results. The shutter of the camera should be set to B (bulb), the lens wide open and focus at infinity, and a cable release used, The observer, watching through another prism or grating, should press the release as soon as the bright-line spectrum appears, and release it as soon as possible after the onset of totality. Another method, whereby the entire change in the spectrum can be obtained by winding the film continuously, will be described in a later bulletin covering special projects. - 3 -
Eclipse Bulletin No. 4 cont'd, 5. SPECTROSCOPIC PHOTOGRAPHY (b) Spectrum of Corona. Photographs of the spectrum of the corona require a spectroscope with a slit, attached to a telescope. The procedure is rather complex and will be described in a bulletin covering special projects. Motion Pictures. Motion pictures can be made of all aspects of the eclipse and the procedure does not differ materially from that used for still pictures. Again, a telephoto lens should b& employed, and filters are necessary during the partial phases. The exposure tine of the film, running at 16 frames per second, is aoout 1/30 second. 5. ONRUSH OF SHADOW Photography of tie onrush is interesting and valuable. The observer should be on a slight elevation, with his camera mounted on a tripod. The moment the Shadow is seen in the distance, tie camera should be started, The shadow moves very rapidly acroSs the surface of the earth, and this speed can be measured if the photographer measures the distance (in feet or tiles) betweefl two landmarks he has photographed, and notes the time for tie shadow tG travel, that. dIstance (measured in 16ths of a second on the developed film) and the direction of travel relative to the line joining the landmarks. REPORT FORMS Photographs of most aspectS of the solar eclipse can be made with modest equipment. If the photographer is careful to record all the fletails of the exposures he has made, many of these will not only be of lasting interest but will also be valuable for making measurements. The attached report form, has spaces for information on all types of photographs. It is hoped tbat those attempting photography will fill out and return this form, if possible with copies of his results, to the National Co-ordinator. * * * * * Additional copies of this bulletin and the report form are available on request. Kenneth Chalk Member of National Eclipse Committee Isabel K. Williamson National Co-ordinator 1963 Eclipse 5162 Belmore Avenue, Montreal 29, Canada