[i_am_hydrogen]

Originally Posted by harls

thanks i_am_hydrogen.. I'll try out your steps.

is photomatix available free on the web, or do you have to pay?

There is, but the free version leaves a watermark.

Originally Posted by edmontonenthusiast

I have some questions. I'm new to SLRs and I got the D40. I've read a bit about some of these things, but I just don't get it.

1) Aperture: how is it supposed to help the image?

2) Shutter: shutter speed and everything doesn't make sense! When I turn the dial too much it goes pitch black, am I going too high for 1/___ sec? I think so but I don't know how to get it just right. Like a waterfall - how to make the water blur or froze.

The Three Elements of Exposure

I. Aperture

Aperture performs two main functions. First, by expanding and contracting, it regulates the amount of light that is let onto the camera's sensor. Think of aperture like the pupil in your eye. Paradoxically, the smaller the F/number, the larger the aperture hole will be. For example, F3 will let in much more light than F12. In photography parlance, smaller F/numbers are called "narrow" apertures because the hole is narrowly open, while larger F/numbers are called "wide" apertures because the hold is wide open.

Second, as Home mentioned, aperture affects the "depth of the field" of a photo. Narrower apertures (e.g., larger F/numbers) create what is known as a "greater depth of field," meaning that the photo is acceptably sharp (or nearly so) from foreground to background, right edge to left edge. Wider apertures (e.g., smaller F/numbers) create a "shallow depth of field." The classic example of a shallow DOF is a portrait in which the person's face is in perfect focus and the background is blurred. The blurred area is known as "bokeh," a term used to describe the rendition of out-of-focus points of light. Three ways to achieve a shallow DOF are: (1) aperture, (2) focal distance, and (3) distance between subject and background. In other words, use a wide aperture, get as close as possible to the subject you want to keep in focus, and try to put some distance between the subject and the area you want to be blurry.


II. Shutter Speed

As aperture controls the amount of light that is let onto the sensor, the shutter speed controls the length of time that light is allowed in. A "slow" shutter speed lets in more light than a "fast" one. Slower shutter speeds can be used in artistic ways to give a sense of motion to a photo by, for example, blurring car lights, smoothing out clouds, blurring airplane propellers, and adding a cottony appearance to cascading water. Faster shutter speeds are useful to freeze sports action.

An important rule-of-thumb is to avoid--when shooting hand-held--permitting the shutter speed to be slower than 1/focal length with which you are shooting. Thus, if your focal length is 100mm, do not use a shutter speed slower than 1/100th of a second. But there is a wrinkle. Most non-full-frame cameras have "crop factors," meaning that the sensor is cropped such that it is smaller than the sensor of a full-frame camera. Without getting into too much technical detail, it is important to know your camera's crop factor in order to calculate your actual focal length. For example, a Canon 40D has a crop factor of 1.6x. This means that 100mm is actually 160mm. Consequently, you would not want your shutter speed to dip below 1/160th of a second.


III. ISO

ISO controls how sensitive the camera's sensor is to the light that is being let in through the aperture hole. It can add an "umph" factor to that light and make an image brighter. Higher ISOs, however, increase the risk of imparting the image with grain or "noise."


IV. Conclusion

At some point, it becomes necessary to better understand the mathematical interrelatonships between aperture, shutter speed, and ISO. Some examples:

- f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32 are the standard full f-stops. Increasing the aperture by one stop lets in twice the amount of light. Decreasing it by one stop lets in half the light.
- Halving a shutter speed from, say, 1/500 to 1/1000 lets in half as much light. Increasing it from 1/500 to 1/250 lets in twice the light.
- A wider aperture allows for a faster shutter speed.
- A narrower aperture forces a slower shutter speed.
- Doubling the ISO doubles the amount of light, which allows you to increase the aperture by one stop or halve the shutter speed. For example, assume the following: ISO 200, f/4, 1/1000. If you double the ISO to 400, you can widen the aperture to f/2.8 or halve the shutter speed to 1/2000.