Being old school and learning about photography before the digital age (when Kodaks Tri-X and Ilfords HP4 film were common and my favourite portrait lens was a Canon 135mm) I always attempted to frame the subject matter as perfectly as possible,without the need to crop the image afterwards in the dark room. Now with full-frame CMOS sensors and Photoshop, framing can be sloppy, especially if one doesnt possess the ideal focal length lens for the subject matter. (Simply crop it in post-production with very little loss of image quality.) But I feel it difficult adopting that approach: it feels unnatural and contrary to all I have learnt as its a shotgun rather than a sniper approach. But what happens when one wants to travel light yet seeks to capture illusive and small subjects such as birds? Weighty glass would be ideal but lugging them around in hot, humid forests (and with a limited budget) is not ideal. Hence the attraction of 1.4X or 2X converters. One of my lenses is a Canon EF 100-400mm L IS lens (on a Canon 5D Mark II), and I am seriously consider one of the extenders.. yes I know about losing stops and perhaps some fidelity, but perhaps that sacrifice is worth it? Id really appreciate any comments from anyone who has used this combination, or similar.