sigma 50-500mm and converter help

[eeyore]

Originally Posted by Tobyh

I can't see me using a 2x though - so far I've not really seen the need for it - for shots like these I use a bag hide to get closer.

I have used a 2xtc with the 170-500 on occasion - normally if it was the only way of getting the shot (for example with stone curlew where you can't get too close in case you scare the nesting bird whilst trying to photo its partner) - the results were okay but you can forget the AF its manual focus only and as taking into account crop factor(on a 20D) you have essentially created a 1600mm f13 you need a very steady rest and high iso or bright light.