62 
HINTS TO TRAVELLERS. 
the head approximately levelled by means of the pocket level, altering 
the position or length of the legs as may be necessary. The camera is 
next screwed on to the stand, and the lens selected which on trial is 
found to include the required amount of subject. For groups or portraits 
a long focus lens with wide aperture, such as Dallmeyer’s “ Rapid 
rectilinear,” 11 in. focus, should be used. The next operation is to focus 
the picture accurately on the ground-glass screen of the camera. The 
focussing-cloth is thrown over the head and the camera, so as to exclude 
the light as much as possible, and while looking at the inverted image 
on the ground glass, the milled head of the rack adjustment is turned till 
the image appears as sharp as possible. The camera is now turned about 
on its vertical axis till it exactly includes the view intended to be taken, 
and the screw is tightened. It may be necessary to raise or lower the 
front of the camera carrying the lens in order to include objects at a high 
or low elevation; if the vertical range of this sliding front is insufficient, 
the camera must be tilted; but, if this is done, care must be taken to set 
the focussing-screen vertical again by means of the swing back, and to 
readjust the focus. The full aperture of the lens should always be used 
for focussing, and if the image is not sharp all over the plate it will be 
necessary to insert a diaphragm in the lens, using the largest that will 
effect the required object. Having then put the cap on the lens, the 
hinged frame carrying the focussing-glass is turned over, and one of the 
slides carrying the sensitive plates is inserted in its place. The slides 
should be exposed as little as possible to the light, especially avoiding 
direct sunlight; however carefully constructed, it is difficult to make 
them absolutely light-tight. The shutter of the slide is then withdrawn, 
and the exposure made by removing the cap from the lens for the 
required time. The time of exposure must be estimated according to 
circumstances, and it requires considerable experience to judge of it ac¬ 
curately. A record should be kept in a note-book of every plate exposed, 
giving the number, date, time, exposure, subject, &c. If the plates 
cannot be developed the same evening, and the slides are wanted for 
fresh plates, they must be packed up again, and should be numbered. 
This is best done by marking the number on the back with a bit of dry 
soap, or in the film with a lead pencil. The image on the plate after 
exposure is latent and invisible, and has to be developed. This is effected 
by pouring on the plate, laid in one of the flat dishes, a dilute solution 
