Abhishek,
I used a 400mm lens with a 1.4x converter. So the focal length was 560mm. Since I was using a 40D camera which has a smaller sensor than a full frame 35mm camera, the crop factor is 1.6. So the focal length is multiplied 1.6 times. So the effective focal length that I was using was 896mm.

We never could dream of such a focal length during the film days.

Cheers,
Sabyasachi