RECREATION. 



xlix 



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TO ESTIMATE CORRECT EX- 

 POSURE. 



When estimating exposure, says F. C. 

 Lambert in the Amateur Photographer, 

 there are no less than 6 factors to be taken 

 into account. 



First, time of year, or, briefly, the month. 

 Midday sunshine on Christmas day is not 

 equal to that on midsummer's day. Outdoor 

 photography is practically over by 4 or 5 

 o'clock on a December afternoon; while 

 at the same hour in June or July we can 

 often get good exposures in a small frac- 

 tion of a second. 



Time of day is another factor. In Au- 

 gust, for example, about 4 o'clock in the 

 afternoon double the exposure would be 

 required that would be necessary at mid- 

 day; and at 5 or 6 o'clock the same after- 

 noon it would be necessary to double this 

 again, or give 4 times the midday exposure. 



Weather must be studied. _ While not 

 under control,- observation will teach the 

 strength, or quality and quantity of light 

 available. 



Speed of plate is, to some extent, under 

 control, for we can buy quick, medium, or 

 slow plates. It is not desirable for begin- 

 ners to change their brand of plates oftener 

 than they can help ; but the experienced 

 worker will learn to appreciate a slow or 

 a quick plate as an advantage under certain 

 conditions. 



Subject classification is important. 



The stop is another factor of importance 

 in estimating exposure. Let the begin- 

 ner here pause, and carefully consider 

 what happens when he changes the stop, 

 say, from f/8 to f/16. Firstly, f/16 is a 

 smaller opening than f/8. It is, in fact, 

 only y 2 as wide, and therefore % as large 

 in area as f/8. It therefore admits only %. 

 of the light for the same shutter speed ; 

 consequently, to bring exposures with f/8 

 and f/16 to an equality, we give with f/16, 



the smaller stop, 4 times as long an ex- 

 posure as with f/8. 



But not only does f/16 reduce the light 

 to yi of what it was with f/8, but also it 

 increases the range of objects in focus. For 

 example, suppose we are using a lens of 

 about 5^ inches equivalent focus, and we 

 focus as sharply as possible for an object 

 10 feet away; then, with f/8 we should find 

 a fairly good range of focus for objects up 

 to about 7 feet from us, and as far away 

 as 14 feet, i.e., our practical range would 

 extend from about 7 to 14 feet. If we 

 simply change the stop f/8 to f/16, we 

 should then find we might have objects as 

 near as 6 feet from the lens, and as far 

 away as 25 feet. By changing the stop 

 from f/8 to f/16, we have extended the 

 focal range from 7 and 14 to 6 and 25 feet. 



Thus, changing from a large to a smaller 

 stop means increase of exposure, a.id at 

 the same time increases the range of dis- 

 tance for objects clearly defined. The for- 

 mer is important when estimating expos- 

 ure; the latter, when considering the artis- 

 tic qualities of the picture. 



Therefore the general rules to be deduced 

 are : 



As the time of year passes from Decem- 

 ber to June, increase the exposure. 



As we pass away from midday to fore- 

 noon or afternoon, increase the exposure. 



As the light passes from brightest to 

 bright, dull, gloomy, etc., increase the ex- 

 posure. 



As the plate speed changes from a low 

 number, say 50, to a high one, say 250, re- 

 duce the exposure. 



As we pass from a small f number, say 

 f/8, to a higher number, say f/16, increase 

 the exposure. 



_ As we pass from a distant or a well- 

 lighted object, say panorama, or cottage in 

 the open, to a near or poorly lighted sub- 

 ject, as a foreground landscape or a similar 

 cottage under trees, increase the exposure. 



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