The focal length of an optical system is a measure of how strongly the system converges or diverges light. For an optical system in air, it is the distance over which initially collimated rays are brought to a focus.hen a lens is used to form an image of some object, the distance from the object to the lens u, the distance from the lens to the image v, and the focal length f are related by. The focal length of a thin lens can be easily measured by using it to form an image of a distant light source on a screen.
1 For killing mold with bleach use a ratio of one cup of bleach per gallon of water (ie about 1 part bleach to 10 parts water). 2  Apply the solution to non-porous surfaces with mold growth either by using a spray bottle or by using a bucket and a sponge or cloth.
You can effectively kill mold on wood in your attic using MoldSTAT + mold killer by soaking the mold growing on the trusses and plywood and allowing it to stay wet for at least 10 minutes then air dry.ou can effectively kill mold on wood in your attic using MoldSTAT + mold killer by soaking the mold growing on the trusses and plywood and allowing it to stay wet for at least 10 minutes then air dry.