This is another 300mm f4 but comes without the luxury of using rare earth glass in its optical formula. It is lightweight as compared with the bigger

This is another 300mm f4 but comes without the luxury of using rare earth glass in its optical formula. It is lightweight as compared with the bigger brothers. Select glasses of low and high refractive indices, used in the rear groups convex fifth and concave sixth elements respectively, equalize to correct field curvature.