Clash of the affordable big zooms!

[Throlkim]

Right, my dad's looking for a lens for birding. Ignore the fact he's a Nikon user!
He can't really go too high in price, £700 is about the limit, which makes the contenders:

Sigma 170-500 f/5-6.3
Sigma 50-500 f/4-6.3
Tamron 200-500mm Di f5-6.3

Which is the best performer optically?
Which is the lightest and easiest to handhold? (he can't carry a tripod too often due to medical issues)
Which has the quickest AF?

I'd be very grateful for any help. He loves birds but currently his longest lens is a 70-300.

[LightRules]

Get the Bigma.

[gasrocks]

Can he handle a monopod? Hope so. They all kinda require one. Don't get the 170-500, doesn't get very good reviews. Either of the other 2 have many followers, Bigma (50-500) probably the most.

[cataclysmcow]

The Bigma would be the best optical performer and definately has better AF than the 170-500. I own the Bigma and have used the 170-500 before and the Bigma is clearly on top. I haven't used the 200-500 before, but the Bigma seems to get better reviews.

The Bigma probably wouldn't be a suitable option though. It's pretty hefty (5+ lbs) and takes a decent arm to hold it steady.

[steved110]

Really, the Bigma is the only contender there. Failing that, he could sell the Noink stuff and get a 100-400 ;) :p

Needs a monopod regardless of what he gets though.

Noink's 200-400 VR is a pretty good lens though.

[GyRob]

Another vote for NOT getting the 170 to 500 mine was rubish so i sent it back.
Rob

[Throlkim]

Aye, a monopod should be fine for him. I'm worried about the weight of the 50-500 though, not sure how easy it'd be to carry for a while. Are there many disadvantages of the Tamron over the Sigma?