if u are using an over head, i think any angle is pretty much a correct angle, unless you are using a large aperture causing a smaller area of focus then you might have to keep changing the angles till u find the best(scheimpflug principl).jcardona1;4046604; said:so are you shooting this in full manual? what were your settings (ISO, shutter speed, aperture) etc. and i usually get lucky with my speedlight as to where it casts a black background.
have you figured out the correct angle at which to aim at the fish?
For the black background just use a small aperture(f15-16), high iso(mine supports the lowest 200 so i use 200), and 1/1000 for the shutter speed, with an over head flash and u shall get the black background every time like a charm