Canon Lens Guide
with sigma sigma lens tele converter?

I bought Canon 450D a few days earlier with the kit lens. 18-55 that is enough for general photo. long-distance wildlife and bird photography or need a good telephoto length. first i cannot afford the high prices of the lenses, Canon 75-300 is not a good option because of poor results and the canon 70-300 is too expensive. so I have to turn back to Sigma 70-300 APO DG MACRO F4.5/5.6, and apart from that I'm thinking of buying 2x converter Sigma APO. this will give according to my calculation going to be 960 mm. (300 focal length x 1.6 x 2). can someone guide me is the fine combination for wildlife and photography bird? any other suggestions would be appreciated.

surprise a pro photographer does not know the conversion factors or that a 2x converter reduces two stops light. The combination will slow to almost useless in AF, these waves will be a handful. bird photography is very difficult and as was better up with a cousin and 1.4. 960 mm sounds good but its optical long stretch there ….. except perhaps a prime number up to 200mm with a 2x will 200×1.6×2 that is 640mm which is quite good and will be 10 times sharper. Just my thoughts.