Originally Posted by audiobomber
The 55-300mm does not have to be stopped down. It's plenty sharp wide open at 300mm. Stopping down makes it better, but it's not a necessity.
Given its price I wouldn't consider it a "consumer" telezoom though - It's 2-3 times the price of its competition.
Edit: Also, hinman got some pretty good bird results with a Tamron 70-300. That said, a longer lens like a Bigma will make things easier, but a Bigma is $1000.
The Tamron 70-300 is a good starter lens, amazing deal for its price.
Sigma 17-70 is a great match for the Tammy to provide a "super kit"
Pentax/Tamron 18-250 is a great travel lens - it's the lens you want when you can only carry ONE lens.
Bigma is long and sharp but it is HEAVY and expensive.