Canon EOS 1D Mark II, Canon EF 400mm f2.8 L IS USM, EF 1.4xII, ISO 800, f9, 1/60, crop.
I normally don't crop. However, I was using the 2xII TC with the 70-200 f2.8 L IS USM lens and had kept the 1.4xII TC attached to the 400mm f2.8 L IS USM lens. The reason being light was low and I wanted 560mm at f4. The extra stop of light was more important than the focal length.
This is how I calculate amount of crop.
Original dimensions = X * Y pixels
Cropped dimensions= A * B pixels
Amount of crop = [(X*Y)- (A*B)]/(X*Y)
This is the amount that has been cropped or thrown away.
Using this formula, the amount of crop in this image = [(3264*4896)-(2476*3714)]/(3264*4896) = 0.4349 or 43.49%
Frankly speaking till the time I calculated this, I had no idea that I am throwing away about 43% of the image. So when someone says that it is a slight crop it becomes very difficult to imagine the amount of crop.