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Old 03-25-2005, 01:39 PM   #1 (permalink)
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Default Avoiding image blur (3 of 3)

In this last post about avoiding image blur I'll explain the camera settings that affect the image sharpness.

1. Shutter speed
Very simply put the shutter speed is the speed with which the camera takes the picture. Here are a few images taken with different shutter speeds:

Fast shutter speed 1

Fast shutter speed 2

Slow shutter speed 1

Slow shutter speed 2

The shutter speed is measured in fractions of a second - 1/8, 1/15, 1/30, 1/60, 1/125 and so on. The greater the divider number the faster the shutter speed - so a shutter speed of 1/125 is faster than 1/8. As a general guideline you should use a shutter speed of no less than 1/30 to "freeze" the movements of fish and plants in your tank. Setting the shutter speed can be done manually on most modern cameras. If your camera doesn't have that option and it sets the shutter speed to a lower number then your only option is to use more light.

Note that all of the above pictures have both sharp and blurry areas. Shutter speed is only one of the things that are important when trying to get a satisfactory picture:

-Some of the leaves of the plant in "Fast shutter speed 1" are out of focus. Also the plants on the background are out of focus. Both of these blurry areas are a result of the focusing, not the shutter speed.

-The tops of the foreground plants in "Fast shutter speed 2" appear white (overexposed). That is an exposure and light diffusion problem, but not a shutter speed issue. The rocks and fish on the background are blurry - another example of out of focus area, but not a shutter speed issue.

- The overall hue of "Slow shutter speed 1" is a bit on the yellow side. That's a "white balance" setting issue. The fish appear as cool colorful blurs which is definitely a shutter speed problem - the camera "took its time" to take the picture and the fish moved around during that time. Such colorful trails are an extreme example of using slow shutter speed and most likely you will seldom have to deal with them. These trails created by the fish are not an entirely bad thing - Amano has a more than a few images in his magazine that employ that to give the image a flowing, even dreamy feeling:

-I choose the "Slow shutter speed 2" picture as an example of a shutter speed that is just a little but too slow to "freeze" the movements of the fish. That is probably the situation that you will encounter most often - a slightly faster shutter speed would produce a sharp image. Note how some of the red tetras appear sharp enough (having in mind the overall softness of the image) but some are definitely blurry. A shutter speed slightly faster would have "frozen" the fish's movement.

Modern cameras usually have shutter speeds of 1 second to 1/2000 of a second. Often only the dividing number is displayed on the camera (8,15,30, 60, 125...). If your fish are too fast for a shutter speed of 1/30 and you need to shoot them with 1/60 you may find that you need more light. Before adding more light bulbs to the tank or before reaching for the flash try adjusting the aperture of the camera;

2. Aperture
In simplistic terms the camera's "aperture" is a "hole" in the middle of the camera lens that you can control - make it big or make it small. It allows you to do 2 things:
- Precisely control how much light enters the camera.
- Adjust the "depth of field" (more about it below).

Aperture is measured in numbers too - the most common range is 22, 16, 11, 8, 5.6, 4, 3.5, 2.8, 2. For now please overlook the seeming randomness of the numbers, but remember that the smaller the number the more light enters the camera. So for example setting the aperture to 3.5 will let more light in than setting it to 8.

Controlling how much light enters the camera is a pretty clear concept to grasp. What may not be immediately obvious is that the amount of light that enters the camera is also connected with the shutter speed. Here's why understanding the correlation of the two is important:

Say you set your shutter speed to 1/30 and the aperture of 3.5 and you get a nicely exposed image. But some of the fish in the picture are blurry. It'd make sense to set the shutter speed to a faster one - say 1/60. But with 1/60 and aperture of 3.5 your image comes out too dark (underexposed). Setting the aperture to a wider one will result in a proper exposure - 1/60 and 2.8 will work. The shutter speed and the aperture are linked. You will get the same exposure with the following combinations:

1. 2 sec. - 22
2. 1 sec. - 16
3. 1/2 - 11
4. 1/4 - 8
5. 1/8 - 5.6
6. 1/15 - 4
7. 1/30 - 3.5
8. 1/60 - 2.8
9. 1/125 - 2

Notice that some of the shutter speeds above are too slow. Fish and even slow moving plants will appear smeared. As mentioned before - try to shoot with a shutter speed of 1/30 or faster. The combinations of shutter speed/aperture listed above may seem redundant because all of the combinations provide the same exposure. But the image produced with combination (1) will differ from the image produced with combination (9). The so called "depth of field" of the first image will be much greater. Look at the images below:

In this image the fish on the background is blurry because the depth of field is very shallow (meaning the aperture was opened wide). Closing the aperture would result in both fish being sharp.

Here's another example of a shallow depth of field (wide aperture). The plant in the center is in perfect focus but the fish in front of it is out of focus. Closing the aperture would result in both the plant and the fish being in focus.

And this is an example of a wide depth of field. Note how all the plants in the tank, from the front to the back glass are sharp. Closing the aperture increases the depth of field:

Shallow depth of field is commonly used in portrait photography to accentuate the eyes or the face:

When shooting aquatic plants that same technique helps make a plant stand out of its environment:

Compare the above picture with the one below. This gorgeous red Ludwigia would look even better if the aperture was set to a wide one so the background was blurred a bit.

When you experiment with different shutter speed/aperture settings you will notice that often you need additional light. Closing the aperture requires stronger light. Using faster shutter speed also requires stronger light. Once again - before adding more light bulbs to the tank or before reaching for the flash try adjusting another setting of the camera - the "film speed".

3. Film speed (or ISO rating)
Obviously digital cameras don't use film but besides the shutter speed and aperture your camera has a setting that you can adjust if the light is not enough (or too much). The ISO ratings is also measured in a weird sequence of numbers - 100, 200, 400, 800 being common.

Here's how the ISO setting will help you get a sharper image without changing the light:

In this example a correctly exposed picture is a result of using an ISO of 100, 1/60 (shutter speed) and 3.5 (aperture).
By changing the ISO setting to 200 the camera becomes more "sensitive" to light. That means that you could shoot the same tank with a faster shutter speed setting of 1/125 and 3.5. To a get a wider depth of field you would keep the same shutter speed - 1/60, but close the aperture to 4.

Setting the ISO to 400 will allow you to go even faster - 1/250 and 3.5. Or get more depth of field by using 1/60 and 5.6.

The following tables may show things clearer for you. All the combinations below result in a correctly exposed image:

Faster shutter speed, same depth of field:
Shutter speed--Aperture--ISO
125 -------------3.5-----200
250 -------------3.5-----400

Same shutter speed, wider depth of field:
Shutter speed---Aperture--ISO

At ISO settings of 800 and higher some cameras have a tendency to decrease the quality of the image. That is not a problem in newer and more expensive cameras. In the written example above the first image was taken with 1/60, 3.5, and ISO 100. Using a high end camera will allow you to shoot with 1/1000 and 3.5 at ISO 1600 or with 1/60 and 11 for an extremely wide depth of field.

An important detail about depth of field is that it decreases greatly when you get closer to your subject. Macro photography deals with very, very shallow depth of field (1/4" is considered wide) and using a lot of light, a tripod, and all the other ways to avoid camera shake are of utmost importance:

Keep in mind that often your images will appear less sharp when posted on the Internet because of the different ways of compressing the files. As mentioned before - getting the sharpest original image possible, with the least amount of digital editing is the best approach. Digital editing will be the topic my next few big posts here.


Last edited by niko; 03-25-2005 at 04:58 PM..
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