448 On Sun Pictures. 
Several square boards a little larger than the paper, 
And some large camel’s hair brushes. 
Before I describe the mode of preparing the papers, 
something may be said about the Camera that I use. 
Being desirous of taking views of a rather large size, I 
felt that unless some means could be contrived for diminish- 
ing the size of the Camera, the apparatus would be too bulky 
to be carried about without the aid of two or three persons, 
The focal length of my lens was about 21 inches. I 
therefore, when lately in London, ordered a Camera to be 
made 24 inches in length, 15 in width, and 13 inches in 
height, and without a top, which I replaced with a double 
fold of black calico. 
_ The ends were made to slide into grooves, and the sides to 
fold with hinges flat upon the bottom, which greatly lessened 
its bulk, and made it easy of carriage. 
The stand for the Camera is of French manufacture, has 
folding legs, and is light and portable. 
My lens, which is by Ross, of Holborn, TonIeAy. is a 
compound double achromatic one, of 8} inches in diameter ; 
when used for the Daguerreotype, it has a focal distance of 
about 12 inches, and will cover a plate of about 5 by 4 inches. 
To adapt it for the Calotype process, I unscrew the two 
glasses next to the paper, and substitute for them the glasses 
from the opposite end, with the convex side next to the 
paper: ithas then a focal distance of about 21 inches. ‘To 
correct the aberration of the rays of light, I place at about 
21 inches in front of the lens, a diaphragm which has an 
aperture of only a quarter of aninch. A large quantity of 
light being thus cut off renders the time of exposure very 
much longer; but as a compensation, the details of the 
picture are much sharpened, and the lines at the sides are 
tolerably straight. 
