CHAPTER VII. 
EXAMPLES OF PROCEDURE. GENERAL 
ROUTINE. 
TN the actual procedure for making a photo-micro- 
-*■ graphic negative certain steps must always be 
taken, some others vary according to the class of work 
to be performed. In every case the optical system, the 
lighting and the plate, must be “ centred.” 
i.—To Centre the Condenser. 
Affix to the tube in the ordinary way a low-power 
objective, say iin., and an ocular. Put the condenser 
into its place in the substage ; insert into the condenser 
a very small stop, or put on its “ nose” a pinhole cap 
which is supplied with condensers which have no iris. 
Throw a beam of light on the back of the condenser, 
and find the image of the small stop in or on the 
condenser, looking through the ocular and objective ; 
by means of the centring screws of the substage get this 
stop-image accurately into the centre of the field. 
2.—To Centre the Light and Focus the Con¬ 
denser. 
Put an object on the stage, and focus it with the 
objective ; having removed the small stop from the 
condenser, rack the condenser up or down till, 
possible, an image of the radiant is seen sharp across 
