<snip> I have an F5, an F4, and a TC-16A. I usually use the TC on the F5 with a manual 300 mm f/2.8. It makes for a pretty fast-focusing 480mm f/4.5. I've been quite pleased with the performance of the combination. I've also used the TC with other lenses and never seen the focus problem. Given you admission to pickiness, would you say this effect is so small that others wouldn't notice it? <snip> VFN sent this message as a reply to a question/comment from Don. My question is, has anyone tried a similar combination: The 400mm f/3.5 and the TC-16A on an F5? This should, according to my 'calculations', yield a 640mm f/5.6 that is semi-autofocus. My interest is in shooting (1) baseball games, and (2), animals in nature, where you need long lenses. I would lose matrix metering, but it's a lot less expensive than a 600mm f/4 AF-I or AF-S. Thanks, Colin
