When taking black and white infra-red photographs special focusing adjustments must be made because infra-red rays do not behave in the same way as visible light. The point of focus for infra-red radiations is further from the back of the lens than it is for white light, and a small degree of focusing compensation is necessary to produce sharp infra-red photographs. In fact the lens must be adjusted as if the subject were slightly closer. Read the rest of this entry »
Joint boxes are usually circular and for part of the circuit wiring. They are fix permanently to the house structure are used principally in lighting circuits. Join boxes are available in 4- 5- and 6-terminal versions.
A 3-terminal joint box of 30 A current rating is used for ring circuits to connect spur cables to the ring cable, as shown the illustration. Read the rest of this entry »
