Quote Originally Posted by pgowder
Why does it cost SO much more to make a lens f2.8 as opposed to f3.5 ro f4?

Thanks!
The glass they use in these lenses is also different, higher quality, and harder to manufacture and because of the higher attrition rate in selecting glass that meets the tighter standards at larger sizes to achieve the faster apertures, you end up paying more. And the list goes on...
BUT....they're worth it. I tried to live with the 28-135 f3.5-5.6 IS USM as a fill in lens after my 28-70 f2.8L and 70-200 f2.8L zooms were stolen 3 years ago, but it just wasn't the same crisp, contrasty images that I was getting on my pro zooms. So I gave myself a hefty Christmas present 2 Yuletides ago and got the 20 f2.8, 50 f1.4, 85 f1.8, 135 f2L, 28-70 f2.8L, 70-200 f2.8L IS, and both the 1.4x and 2x extender II's. Now, I'm happy again
They're worth every penny.