Lenses that transmit UV are very expensive, because (much like infrared lenses) they must be made from special materials. With thermal cameras, resolution is very low anyway, so the aberrations from simple meniscus lenses are not too apparent: UV photography is much more demanding and lenses are correspondingly more sophisticated. Far ultraviolet (below 200nm) is blocked by virtually all materials and even oxygen in the air, so this spectrum is still largely unvisualized.