[sammcdonald]

i have 2 tamron 100-300AF and a manual 400 (and a doubler) which i use on a km maxxum 7d (6.2 slr) and a sony alpha (10.2 slr). i use a minolta 70-210 primarily on the sony. the tamron is a good glass older lens...some good tamron and some cheaper ones.
for using the doublers and making the lenses absurdly long, you gotta have it on a 'pod or a cornbag to keep it steady....over about 300 the shots get more and more fuzzy unless properly stabilized.