Originally Posted by reefrunner69
When taking pics of moving objects, there is no way around it, you gotta be using a faster shutter speed, this means you either use the lash, or you fiddle with the exposure. For the pics of the clown I took (in the new aquisitions forum), I had the exposure bumped up to +2.0 EV, I had the camera stopped down to an aperture of about 3.6-4.0 (lose some depth of field, but it allows more light in) and an ISO equivelant of 200 and a shutter speed of 1/60sec. It's about capturing the light, slower shutter speeds allow you to have a larger aperture, which increases your DOF, but it makes it pretty hard to prevent motion blur.
I think you got a little confused here. Increasing aperture size (smaller number) will REDUCE your depth of field, but allow you to take in more light at a given exposure time. Decreasing the aperture size will increase depth of field, but require longer exposure times to take the same photo. For example to take a perfectly exposed picture of a cactus in the desert you could take the shot at f/2 and a shutter speed of 1/10000 of a second or get the same shot with f/16 and 1/1000 of a second. The difference will be in the first one the background will appear blurry while the cactus is in focus, and in the later both the cactus and the background will be sharply in focus.
Aperture size is calculated by f/N, f being the focal length of the camera. N is the number that you choose on the camera to determine aperture size. In low-light situations where you have movement that you want to freeze you are going to want to choose the smallest f-number you can on your camera. This will allow you to take in as much light as you can for the chosen exposure time. The side effect will be an out of focus background, just how out of focus depends on the f-number chosen and the distance of the background from the subject.
If you are in high light situations or you have adequate light and want to maintain a greater DOF then you can decrease the aperture size by choosing a larger f-number. Remember not as much light will get in per unit time with a smaller aperture but in well lit aquariums you can get away with this smaller aperture size.
The key to picking an f-number is remembering whatever you choose the aperture size will be it's reciprocal. IE f-number 2 is actually f/2 so that is a larger aperture size than f-number 16 = f/16
As mentioned by reefrunner69 you can further enhance your picture taking skills by toying with the EV value on your camera. This is the exposure value like it's name suggests is a way of changing the way your camera exposes images. First I will talk about the case where a light source causes your subject to be UNDEREXPOSED (subject is too dark). In this case you will want to choose a + EV value to compensate and make the subject brighter. In the case where your subject is OVEREXPOSED (subject is too bright) you will want to choose a - EV value to compensate. This wont necessarily help with there not being adequate light in the aquarium but it can help when reflection of light off the sand causes a ground dwelling fish to be underexposed.
If you have increased your aperture as big as you can get it (small f-number) and toyed with the EVs and haven't been able to capture that shot of an active fish you have another option. Digital cameras have another way of adjusting in low-light conditions. It's been brought up a little here and that's called the ISO setting. Generally you want to keep your camera on the LOWEST ISO setting you have, because this allows you to take the best quality pictures. When you bump up the ISO number, you are in effect making the millions of optical sensors in your camera more sensitive. The more sensitive these sensors become the more noise will be evident in your images.
This is where the recommendation of taking LOTS of pictures comes into play. Different cameras respond to the same ISO settings differently. For example, ISO 200 on my camera may introduce the same amount of noise into an image as ISO 800 on a different brand camera. By taking pictures and toying with the ISO settings you can see how high you can set your ISO to before it introduces too much noise for your liking. If you have to go with a high ISO don't be discouraged, there is software that can help reduce noise in images, and techniques that can be done in Photoshop to reduce noise as well. (Besides using the reduce noise filter)
Now to put all this together to take those perfect shots of your fish. If you have some highly active fish like a danio you are going to want to have a fast shutter speed to effectively 'freeze' them in the picture. Play with varying combinations of aperture size, ISO settings, exposure values, and shutter speeds to take a picture you like. I can't tell you what exact settings will work best for your aqarium shots because as I said earlier all cameras are different, and your lighting will more than likely be different than mine. However if you want I can help steer you in the right direction so you can start taking those breath taking shots. I may be a newbie to FW
aquariums, but I know my fair share about digital photography and would love to help fellow members out since I will undoubtedly be requiring assitance from you.
Let me know if any of this is hard to understand or needs better explanation I wrote this a little tired with little proof reading. If there is enough interest I can probably have a thread where I can answer more photography based questions, or setup a time where I can host a chat on instant messenger and answer questions in realtime. This just covered some of the basics of photography.