>One other thing I never see mentioned is that the size and weight >reduction for these 'APS' size lenses will be (much) less for >teles than it might be for Wide-angles. > >A 300mm f/2.8 will have a front-lens of just over 100mm by definition! > >Not much weight or size to be saved in my opinion ...
Here's an interesting illustration of exactly that point. I got the dimensions of 400mm F5.6 lenses for both 35mm and 645 from the Pentax USA web site and put them below. Notice that the front element is the same diameter and the weight is almost exactly the same: smc P-FA 645 400mm F5.6 ED (IF) (w/case) Filter Size: 77mm Maximum Diameter & Length: 83mm x 252mm Weight: 1,250g (44.1 oz.) smc P-FA* 400mm F5.6 ED(IF) (w/case & hood) Filter Size: 77mm Maximum Diameter & Length: 3.8" x 10.4" w/hood Weight: 40.2 oz. --Mark
