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4. By means of the grooved rim of the
f l a s h g u n ' s c o n t r o l d i a l , t u r n i t u n t i l t h e
i n d e x i s a l i g n e d w i t h t h e s p e e d r a t i n g
o f t h e f i l m i n u s e . ( D o t s o n t h e
film-speed scale represent ASA ratings
o f 3 2 , 4 0 , 6 4 , 8 0 , 1 2 5 , 1 6 0 , 2 5 O , a n d
3 2 O o r D l N i n d e x e s o f 1 6 , 1 7 , 1 9 , 2 0 ,
22, 23, 25, and 26, respectively from
l e f t t o r i g h t . )
5 . T h e c o m p u t e r w i l l v a r y f l a s h d u r a t i o n
f rom 1/600 to 1 120,000 sec. to pro-
v i d e a u t o - f l a s h e x p o s u r e a t t h e r a n g e
o f f i v e F - n u m b e r s a p p e a r i n g i n t h e
g reen area v isib le th rough th e apertu re
s c a l e . T u r n t h e c o n t r o l k n o b t o s e t t h e
w h i t e i n d e x a t t h e d e s i r e d a p e r t u r e
w i t h i n t h i s r a n g e . * ( T h e i n d e x m a y b e
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