[gts055 (Mark)]

Assuming the glass is of the same selected quality, ie, free of faults such as internal stresses, bubbles, color and striae, and the refractive indices of the mating elements have been selected correctly, then the only advantage in using FPL53 over FPL52 or FPL51, is that a shorter focal length can be achieved, and still give a near "color free image". High quality optical glass, of any type, comes at a premium cost. Stating FPL53 or FPL51 or whatever, means nothing, it all depends on the grade of the material. This is apart from the time taken to figure the lens set and mount them into a stable cell etc.
Regards Mark