Provided are silica-based fine particle dispersion sols, processes for producing the sols, coating compositions containing the dispersion sol, curable coating films obtained from the coating composition, and substrates having the coating film. The optical member has plural layers on a substrate, and includes at least one metal oxide layer having a void, and at least one layer containing an organic resin as a main component formed between the substrate and the metal oxide layer. The imaging optics system has a plurality of cells each being an independent optics system arranged in a main scanning direction, and arranged in two rows in a sub-scanning direction. Calculators calculate functions of the values of the parameters and further comparators compare the functions with thresholds.