This series of news articles is intended to help the novice digital photographer who wants to learn more. The aim is to explain key terms and introduce new ideas to help you, as a novice, explore the world of digital photography.

Understanding Exposure; the good the bad and the ugly!

We talked a little in the [link]"previous edition of EDP about shutter speed, aperture and ISO and today we’re going to take that a little further. This article is specific to DSLRs because most general digital cameras have very limited options when it comes to adjusting your exposure (they do it all for you). But, by all means read on and learn something new even if you don’t own a DSLR yet!

In terms of photography, exposure simply refers to the total amount of light you allow through your camera and into the image sensor to record your photograph. While most digital cameras can handle some exposure error and compensate for you automatically, understanding exposure can really help improve your photography.

So why is it important to understand how to manually control the exposure on your digital camera? Well, too much exposure, and your photos will be bleached or washed out, too little and they’ll be too dark to see anything. While it’s possible to correct your photos in software such as Adobe Photoshop at home, there are a few reasons why you should avoid this:

If you overexpose your photo, you’ll end up with "blown highlights" (you know, that bleached cloud look?). It’s the same with under-exposed images which come out too dark. Basically, if your camera doesn’t capture the detail, you can’t recover it later!

The colour saturation and contrast of poorly exposed images is quite noticeable and often quite ugly (unless you know what you’re doing).

Taking the time to correct the exposure while you’re taking the shot will save you more time than trying to correct it later at home in Photoshop or similar software.

Ok, so on with the most important things! There are three main things that can make a difference to the exposure of your image; Shutter Speed, Aperture and the ISO Setting. Previously we talked about these individually, but now I’d like to talk about how they work together to give you a better image.

Shutter Speed

The first major part of understanding exposure, is learning to understand and better control your cameras shutter speed. The shutter speed is a measure of how long the shutter stays open when you take your photograph. While your shutter is open (think of it like a window), light can enter the camera and fall on the image sensor.

The longer the shutter stays open, the more light enters the sensor and is recorded on your image. If you leave the shutter open for too long, the photo will be overexposed and the image will come out too bright.

When we’re talking about shutter speeds, it’s probably important for you to know that we’re only talking fractions of seconds. In fact, 1/30th of a second is generally considered a slow shutter speed! It’s common for a digital SLR to be capable of shutter speeds in excess of 1/4000th of a second!

Examples of images taken with a fast shutter speed (like below), show you just how quickly the shutter opens and closes in order to focus on the subject (often fast moving) and take the image. Images taken with a fast shutter speed should be crisp and in focus.




Examples of images taken with a slow shutter speed (like below), show you just how magic an image can look when you slow things down a little. Notice how the things which are in motion appear blurred, and those which were still are clear and sharp.

The Aperture

Well, you know from the last edition that the Aperture is simply an adjustable hole in the lens which also allows light onto the sensor. You can adjust this hole and therefore allow more or less light in, depending on the conditions you’re shooting in.

You also need to be aware that the Aperture and shutter speed work together - if you slow the shutter speed (letting in more light) you have to close the aperture to compensate. It works the other way around too, if you have set a fast shutter speed (letting in less light) you have to open the aperture to allow in more light to compensate. Huh? Have I lost you yet? Ok.. read on.

Shutter Speed and Aperture working together

So, let’s put these two together and think of this in simple terms. A correctly exposed photo might need say 1000 "units" of light to hit the sensor and record the image as you see it.

If you let too much light in (say 2,000 units), your image will be over-exposed and will looked bleached out, especially the light sections such as skin, clouds and white garments. If you don’t let enough light in to the camera to expose the image (say only 500 units), then the photo will be under-exposed and it will be too dark to see any detail.

One way you can gain the correct exposure is to open the shutter. If opening the shutter speed for half a second lets in 500 units of light, doubling that to one second will allow in the 1,000 units you need and the image should look just right.

The other way your camera can allow those 1,000 units in is to open the aperture. So, the shutter speed can stay at half a second, but make the aperture twice as large and let that little bit of extra in that same half a second.

A fantastic example of shutter speed and aperture working well together can be found in *DuvallGear’s work:

and


It’s difficult to capture this sort of scene perfectly at the best of times, but when you want to try this at sunset, you’re most likely going to have to practice getting the exposure just right in both the foreground and background. This could almost lead us into discussing HDR Imaging and the various aspects of blending various images at different exposure settings together, but we might save that for another day (there’s a link to another dA news article about HDR at the bottom though)!

Taking long exposure shots like *DuvallGear’s shown above are not far out of your reach! The combination of the long shutter speeds (and unless you have steady hands, you’ll need the tripod), larger aperture (smaller hole) give results like this! With the camera steady, any object which remains still will stay in perfect focus, and any moving objects (like water or clouds), will come out softer and slightly out of focus (motion blur).

ISO Setting

The last point I want to discuss with you here, is the ISO Speed for your camera. We discovered in the last edition, that the ISO rating is simply the measurement of how much light we allow onto the sensor; think of it like absorption. In traditional photography, it generally referred to how sensitive your film was to light (or film speed). If you’re shooting outside in the evening, chances are you’re going to set the ISO at a higher level, so your cameras sensor "absorbs" more light.

So, how does this help with controlling your exposure? Ok, imagine your set to take a photo: your aperture is fully open (to let as much light in as possible), and the shutter speed is as slow as you can manage without a tripod, and you still don’t think there’s enough light?

Well, you increase the ISO setting. You have a few options to chose from when you go to your ISO settings, anywhere from 100 (low) to 1600 (high). Lower ISO settings are usually used when you have enough natural light around you and the higher settings are usually used at night or indoors where there might be less light.

It’s important to remember that your ISO setting will not only determine how much extra light you allow to be absorbed by the sensor but also the overall quality of the image, so be careful when using this option. Higher ISO levels will result in more "noise" and excessive noise will result in a poor quality photo, so it’s standard practice to use the lowest ISO setting possible.

Go and look for yourself

To finish things off this time round, I thought I’d feature some great work, many of which are interesting in their own way. Be sure to go and look at the images and then check out the photo’s Exif data under the view count of each deviation (really the most important information if you want to learn). Check out the various settings people have used to achieve the results they have in the details of the images they’ve presented!






Some links to consider
If you’d like to have a play, there’s a great website http://www.photonhead.com which has an online camera simulator you can play with to learn more about exposure. Give it a go!

If you’re interested, you can read more about HDR Imaging here.

Future Editions:
Rule of Thirds
Lighting and Flash
Optical vs Digital Zoom
Lenses and Filters
Special Photography Secrets
Macro special…

Previous Editions
EDP Edition #1
EDP Edition #2

Thanks for reading. Feel free to send a note if you've got a suggestion for future editions of EDP!

Cheers,
Cath