42 AMPLIFICATION 



it will require an exposure of 1,000 seconds 

 (just over 16 minutes), if the amplification is 

 to be 200 diameters. 



Thus 200 = 10 

 20 



10 2 = 100 



100 x 10 sees. = 1,000 sees. 



= 16 mins. + 



If the exposure of an object be lj- mins. 

 when the amplification is 45 diameters, the 

 exposure will be 13J mins. if the amplification 

 is to be 135 diameters. 



45 2 : 135 2 : : Ij mins. to 13J mins. 



The magnification can be calculated approxi- 

 mately when no eye-piece is used, thus : 



With a 1-inch objective and a 40 inches 

 focus the magnification should be 40 diameters. 



Or, with a ^th objective and a 30 inches 

 focus the magnification should be 30 x 6 = 180 

 diameters. 



But as the objectives are not always 



