Quote Originally Posted by Kayaker72
I had been thinking of doing something like that but with the 70-200 L (non-IS). After reading your post, I evaluated the 70-300 mm IS again.

I suspect the 70-200mm f/4L non-IS would be a better choice. If you look at the ISO 12233 crops from either the 1DsIII or the 40D, the 70-300mm non-L is not bad at 200mm, but loses a lot of IQ by 300mm - as Bryan states, that's the worst part of the range. I think you'll find the optical quality of the 70-300mm non-L to be better than your 75-300mm, but noticeably worse than your EF-S 15-85mm lens. Also, the build quality of the 70-300mm non-L is not great. Better than the 75-300mm, but no true USM (it's a micromotor, which is slower then ring USM and doesn't offer full time manual), and the front element rotates with focusing.


One other option to consider in your budget - the 70-200mm f/4L IS plus either the 85mm f/1.8 or the 100mm f/2.8 non-L macro. You'd be giving up 100mm on the long end of the telezoom, but getting a constant aperture lens.