What can be really frustrating about the process, is that each setting you can adjust will to some degree affect the influence of the other settings on the image.
In other words, adjusting shutter speed impacts on aperture and adjusting aperture can impact on the effectiveness of a particular shutter speed. Changing the amount of light used will then alter how a particular aperture setting works and will more than likely cause you to alter the shutter speed once again.
Not only that, but the colour of the fish being shot could command different settings than another fish in the next tank. LOL
Randy, here's another quick lesson to help.
Shutter speed is about how quickly the opening to the sensor opens and shuts.
Aperture dictates how open the shutter is. Typically the lower the aperture, ie F2 means the shutter is more open than say F13. Aperture dictates how much light is allowed into the sensor chamber. The tricky thing about aperture is that the less light allowed, the more depth you can get in an image. So if you shot a profile of a fish with an aperture of say F4, the picture will have much more of a 2d/pancake effect on the image than if you were to shoot with an aperture of F20, which would give you much more of a 3d effect. But closing off the amount of light allowed in with such a high aperture setting means you need to increase the amount of light. A lower aperture setting like F5 requires much less light for the sensor to capture good detail.
Always remember that more light = more detail. You cannot see good detail in subdued lighting. A sensor cannot capture good detail in dim lighting.
ISO dictates the sensitivity of the sensor to light. The higher the ISO, the less light required to capture the same image. However, with less light, less detail can be captured and so pics tend to appear very grainy, the higher the ISO setting is. The sensor gives up detail in favour of a brighter image.
So to shoot without flash requires one to typically crank the ISO.
I could slow down the shutter speed to allow more light in, but then the image becomes blurry because the shutter is not fast enough to catch a crisp image of a moving fish. I could decrease the aperture to allow more light in, but I lose the 3d effect and the image takes on that flat/pancake appearance. So if I haven't stated it clearly enough yet, changing each setting alters the way the other settings work.
Also:
Nikons have typically been poor performers using high ISO settings until the D300 and D3 came along. Canons have always been better with high ISO performance until the D300 and D3 came along. The difference was in the sensor used. CCD sensors, the seonsors used in all older nikons up to the D200, do not do well with high ISO. CMOS sensors, the sensors in the canons and the newer nikons do a much better job. The cmos sensor in the D90 is not as good as the cmos sensor in the D300 and D3, but is much better than the old ccd sensors.
. I know you use a flash on top of the aquarium but how many do you use? I am borrowing my uncle's Nikon D90 with sb600 flash overhead and I cant make the fish stand out in the black background like you do. I'm testing this camera out before I buy my own Nikon D90.
