"Exposure"

[Sergio]

What exactly is exposure? I'm kinda confused.

If my shutter speed is really low, my exposure is higher right?

If my ISO is higher, is my exposure higher?

I simply need to know what technical term is exposure, I'm not sure if it's shutter speed, ISO, or something else. I need to know because I need to shoot multiple pictures in different exposures to create an HDR image.

[Tiberius]

Exposure is actually a combination of shutter speed, aperture and ISO.

I've created a tutorial for it on DeviantArt, which can be found HERE.

I've also got a tutorial about some basic exposure settings HERE.

[Sergio]

Thanks I will take a look at them. I haven't had much time to experiment with my camera. I always got confused with aperture too, I barely learned how to change it right now.

EDIT: I've barely read the second tutorial, and I've learned a lot so far. Great tips!

[moracca]

When dealing with HDR images, exposure is handled a bit differently than in some other situations. I didnt get a change to read the tutorials posted above, but one quick thing I'll mention is that by changing the aperature size (f/stop), a smaller number (2.8 for example) means a larger aperature, and therefor more exposure, whereas a larger number means a smaller aperature and less exposure. Similarly, changing the shutter speed will also change the exposure. Faster shutter speed means less exposure (less time for light to hit the sensor). Normally you can compensate one by the other, ie, if you have want a faster shutter speed, you can user a larger aperature size (a smaller number) to make up for the amount of light you lose by speeding up shutter time. For HDR tho, you want to vary your exposure by changing the shutter speed only, not the aperature size. This is because in adition to changing the exposure amount, changing the aperature size will also affect your depth of field, in other words how much of the picture is in focus. This means that you wouldn't want to use it to get the different exposures on an HDR image, because you want all of your images to be as identical as possible (except for the varied exposure). For HDR it is recommended to change the shutter speed to get the different exposures. This is usually done in 2 step intervals. A "step" is defined as a halving or doubling of the previous setting, so one step up from 1/2 a second would be 1 second, and one step down from 1/2 a second would be 1/4 a second. Say your ideal exposure was at 1/15 second. If you were going to use 3 exposures for an HDR image, you would want one at 1/4 (1/8 = almost half of 1/15, 1/4 = half of 1/8), one at 1/15 sec, and one at 1/60 sec.

Someone please correct me if I'm wrong. Hope this helps!

[wulf]

The most useful explanation I've come across is to think of a triangle. The area of the triangle is the rate at which incoming light is turned into the final picture. The three sides of the triangle, all of which can be adjusted to affect the overall area, are film speed (ISO), aperture (f/stop) and shutter speed (in seconds or fractions thereof).

The science of taking a picture is based on judging how much light is available and then adjusting the parameters in your control to get a resulting picture that has a suitable spread of tones and doesn't lose information in black (no light captured) and white (too much light captured) areas.

The art of photography is understanding the side-effects of adjusting each of the settings and making a decision that results in the image you intend. Tiberius' tutorials have some good information on this. The best way to grasp it though is to experiment yourself - take pictures, adjust settings in a methodical way and examine the results.

Wulf

[Sergio]

Thanks guys, you're a lot of help. Hopefully this makes my hdr photos look better.

[xxpinballxx]

Tiberius, I read your write up on the aperture shutter and ISO settings.
very well done and cleared it all up a bit more fore me. I knew what they meant but not sure how to adjust and use them for certain circumstances. thanks for the link.

[Tiberius]

Glad it helped, xxpinballxx. If you've got any questions, feel free to ask.