630406Eclipse4_p1

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                          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 edlipse were listed and an outline of equipnent necessary for sach 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 equipuent 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 shcw 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 filna and exposure tines, 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 tTf/ stop" can be found by dividing the focal length of the system
used by the clear aperture of the lens.

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