The oil spaced lens doesn't need extensive figuring of the internal optical surfaces, any minor error and roughness is tolerable since the oil compensates these errors, as a result, only the most front and rear air/glass interfaces need to be figured accurately, this brings down the production cost. However, the tradeoff is less freedom for lens optimization.
A good air-spaced objective lens must have all its optical surfaces well figured(e.g. a triplet has 6 nos), the pay back is more freedom for performance enhancement however at the expense of more polishing work and cost. |
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