Opinion on replacing Minolta AF 100-400 APO.

Locally there are a couple of Tokina AF AT-X 80-400mm tele-zooms for a shade under £300.00, though if this was one for further consideration should there be a copy near you, check it on Dyxum lenses section first.  There are quite a few really excellent options for your budget, but it's a nice problem to have, but more difficult than one might think, so getting the right one is the hard part.  It may help narrow the field down by listing what it need to do for you and the intended purposes it's going to be used for as it could be that both prime and zoom options may be available but a single lens type solution no doubt would be preferable.  That said, there is normally the option to add a 1.4x TC to extend it's focal range, though having done so myself, I'm not a big fan of TC's but they do have their uses under certain conditions.

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Mark @ Sonolta * Photography