Richard my experience with that lens was that the quality dropped off significantly with the older 2x. I got rid of it quickly. The 1.4 x was fine and lived on it.
When I upgraded to the Mk II 500, I found the Mk III 2x worked well with it.
Trip Report by Mate and Fellow Traveller Garry Wilkinson
This may seem like a strange title for a report on our field trip to Gambia 9th March- 16th March 2017 but the reason for it will become clear.
Trip participants were Nigel Moore, Martin McClenaghan,William Smiton and...
Help needed to ID this small bird seen by a friend near Tendaba, Gambia last week. It was skulking in the scrub. Robin sized with a pale eyering. Sorry about pic quality. Behaved like a Robin and reminded him of a Red breasted flycatcher.