The apparatus for automatically focusing an image in a microscope includes onto an object plane includes an optical system configured to form an optical image of a sample plane to be observed, an autofocusing detection system, and a focus correction system. The filter includes a predetermined array or stacked arrangement of variable transmission regions that mirror the spatial etch distortions caused by the plasma etching process. The slider arm member is seated on the frame member, and has a biased distal end, and is movable between a closed position whereat the distal end is positioned adjacent the clamping region of the clamp member and an opened position whereat the distal end is positioned spaced apart from the clamping region of the clamp member. Messages directed towards offline members of the persistent instant messaging group are transmitted to such members when they come online. The preservatives include organic acids and the salts and esters thereof but exclude preservatives which can generate sulfur or chlorine-containing compounds.