Page:The peregrine falcon at the eyrie (IA cu31924084757206).pdf/92

 72 more useful than King's, because our methods are, perforce, quite different. He is photographing more or less all the year round, and with constant practice turns out a properly exposed negative without being afterwards able to give you details about light, stop or shutter speed. I, on the other hand, am restricted to about a fortnight each year; therefore I have to pay great attention to detail in order to get good results. He is like the normal individual who can rise from his chair and walk out of the room without thinking of how it is done. I am like the poor man with locomotor ataxia, who has to repeat to himself, "Now I must bring my feet back under the edge of the chair, now I must lean forward and straighten my hips as I straighten my knees." Accordingly I use a Watkin's standard meter, which looks complicated, but is soon learnt, and test the light whenever I can. For birds at close quarters I always use 100 as the subject number. The only thing I have found of any use with under-exposures is to first of all harden the film with formalin and then develop at a temperature of about 90deg. Fahr. Of course, every fresh bird that you try has some characteristic which has to be studied; that is where some of the sport comes in. The stumbling block in the case of adult Peregrines is the extreme rapidity of the sudden turn of the head. Instead of trying to overcome this by brute force, by giving an extremely short exposure, it is better to wait for the turn and expose directly it is over.

Photographs being more useful scientifically if taken to scale, I have a piece of broomstick with sixteen inches prominently marked on it. When placed on rock C and focussed on the screen it was found that a halfpenny (one inch in diameter) covered five inches on the broomstick, so that the bird photographed on C would be a fifth of life-size, and in afterwards making an enlargement, if I enlarge the image on the negative five times I get the bird life-size. On B the halfpenny covered six inches, showing that the bird would then be a sixth life-size on the negative and in the middle of the eyrie a seventh. As nearly all the illustrations are enlarged, I might state that the largest image among my Peregrines is that of the Peregrine stretching himself. This on the negative measures three and a-half inches from the top of his head to the