PHOTOGRAPHY 



193 



desired, and the diaphrag-m "stopped down" as far as possible. Plate-holder 

 I is slipped into place, care being taken not to move the camera by a sudden 

 jar. The camera cloth is dropped above the holder and allowed to hang 

 down over the slide end. The slide is drawn and put on top of the instru- 

 ment, the black edge always up. The exposure is made and the slide replaced 

 tvitJi the black edge outzcard. This point should receive the most critical 

 attention, as a blunder here will often cause the loss of two negatives. The 

 plate-holder is returned to the receptacle, or merely placed in the back of 

 the camera, which is then closed. The number of the plate, the name of the 

 view or object, the condition of the light, the length of exposure, and the 

 aperture of the diaphragm, as well as the date, are recorded in a notebook 

 for this purpose. The shutter is then opened at "time," the diaphragm 

 thrown wide open, and the front of the camera closed. When distances are 

 short, the camera is often carried tipon the tripod. As a rule, however, it is 

 usually removed, and the tripod folded. In making subsequent pictures, 

 the plates should always be used in their numerical order. 



240. The time of exposure is obviously the most critical task in the 

 manipulation of a camera. The time necessary for a proper exposure varies 

 with the season, the hour, the condition of the sky, the light intensity of 

 the formation, the color and size of the area to be photographed, and, finally, 

 of course, with the aperture of the diaphragm. Fortunately for the ecologist, 

 the variation in light intensity during the season, and even during the 

 greater part of the day, is not great, and can ordinarily be ignored. The 

 beginner will make the most progress by determining the exposure de- 

 manded by his instrument for taking a general view in full sunlight and with 

 the smallest stop of the diaphragm. In standard cameras with lenses of 

 ordinary rapidity, this is usually about one second. This will serve as a 

 basis from which all other exposures may be reckoned until one has worked 

 through a wide range of conditions and can recall just what time each view 

 requires. On completely cloudy days the time required is five to ten times 

 that necessary on a clear day ; filmy clouds and haze necessitate an exposure 

 of two or three seconds. The more open forest formations demand an ex- 

 posure of about five to ten seconds on a sunny day, while the deeper ones 

 require two or three times as long. A close view requires more time than 

 a distant one, since the light-reflecting surface is much smaller. Quadrats 

 require two or three seconds, and individual groups frequently take a longer 

 time. The color of the vegetation plays an important part also : a dark green 

 spruce forest requires twice as long an exposure as the aspen forest, and a 

 grassland quadrat tskes more time than one located in a gravel slide. In 

 this connection, it is hardly necessary to point out that the lighted side of 



