Monday, March 14, 2011

Photography Basics - Understanding Exposure and ISO

by DalyCraftWorks

In these blog posts, I'd like to talk about how to take great photos for your ArtFire studios. Taking great photos requires three things from you: A little technical knowledge, attention to detail, and clarity of intention. I know with a little practice we're all capable of all three, but to start us off I'm going to talk about the most basic technical knowledge because it's important to be sure we're talking the same language before we begin exploring the more esoteric aspects of product photography.
So, let's begin with Exposure.
Exposure is controlled by the available light and three camera controls: ISO, aperture, and shutter speed. This blog post is only meant to explain ISO, but it's impossible to discuss one of these elements without bringing in the other three because they all work together. You can't alter one of them without affecting the rest. To understand the exposure process, imagine what happens when you fill a bucket with water. Once you've picked a bucket to fill, the amount of water needed to fill it isn't going to change. What will change is how fast you choose to fill it.

If you open the faucet all the way, the bucket will fill quickly.

If you open the faucet only a little, the bucket will take much longer to fill.

In the illustrations above, think of ISO as the size of the bucket, available light as the water, aperture as the faucet opening, and shutter speed as time (how long you let the water flow). If you open your aperture wide the available light will pour in, and you'll need a fast shutter speed or your bucket will overflow. If your aperture opening is very small the light will trickle in and you will need a slow shutter speed to allow your bucket time to fill.

Just remember: to achieve proper exposure you need to fill the bucket. But there are many ways to get the job done. So, if you can't adjust the light flow, adjust the time; if you can't adjust the time, then adjust the light flow. If the aperture is all the way open and you still can't get the bucket to fill, you need more light or a smaller bucket. If the aperture is closed down to a dribble and the bucket still keeps overflowing, you need less light or a bigger bucket. If this example is confusing, don't worry. All I really want you to take from it for now is the understanding that there are four variables at work any time you make a picture, they all work together, and you can't change one without affecting the rest.

Whenever I encounter a situation with that many variables, my first instinct is to eliminate as many variables as I can. The fewer variables, the more control I've got, and the greater chance of getting the results I want. Let's look at each of our four variables and see what we can do to either eliminate or control them.

First let's talk about your bucket.
What is ISO? ISO also used to be called "film speed" because it is a measurement of how sensitive a film is to light. The higher the ISO, the more light-sensitive the film. The more light-sensitive a film is, the "faster" it is, because even in low light it can be exposed properly using normal shutter speeds. Less light-sensitive films are "slow" because even outside in bright sun they can be exposed properly using normal shutter speeds. Slower films also have finer grain. The larger the film's grain, the more it resembles the "snow" on your old analog TV set. So, in the world of film, less sensitive, slow films with low ISO numbers like 64 and 100 are used outside in bright sunlight. More sensitive, fast films with higher ISO numbers like 400 or 800 are used inside or in low-light situations, with the tradeoff of larger grain.

Most of us are using digital cameras now, so what we mean when we say ISO now is the sensitivity of the camera's sensor. Each camera manufacturer tries to design its ISO settings to approximate the results you would get with film at the same ISO ratings. The lower the ISO number, the less sensitive your camera's sensor will be to light. Because we're no longer tied to the ISO of the film in the camera, the default on many digital cameras is to let the ISO change automatically in response to conditions. This is usually referred to as Auto ISO. If you regularly shoot your products indoors where light is limited, you might think letting your camera set a higher ISO when necessary is a great idea, allowing you to capture shots you otherwise couldn't get.

The problem with Auto ISO is twofold: It introduces an extra variable to deal with when shooting, and higher ISO settings introduce more "noise" just as faster films had more noticeable "grain." In the case of digital cameras, noise is created when the output of the sensor is amplified to make it more sensitive to light. Because the sensor picks up not only more of the ambient light from the scene, but more of the noise generated by the sensor itself, higher ISO settings can cause noise. If you're using a DSLR, chances are you will be able to shoot at 400 ISO or even 800 without noticing a major increase in noise. Improvements in sensor technology have allowed all digital cameras to produce less noise at higher ISO settings. However, if you are using a compact camera, things can get quite noisy even at 400 ISO.

This is because the smaller size of the sensors in compact digital cameras introduces another source of noise. The smaller the imaging chip used, the noisier the results. The number of megapixels a sensor will capture bears little relation to final image quality. Increasing megapixels on a smaller chip may actually mean noisier pictures. So, particularly when using compact digital cameras with smaller sensors, stick to the lowest ISO settings to control noise as much as you can.

This is important when shooting small items and close-ups as we do in product photography, because noise will make your jewelry look blurry or grainy even if it's actually smooth and shiny. You will see speckles, blotches and fringes, rather than smooth gradations and crisp curves. And if you need to crop and enlarge a small section of a larger photo in order to feature details of a piece of jewelry, any digital noise will quickly become much more obvious. It's a good idea to take your camera off "Auto ISO" and set your ISO manually, if possible, so your ISO remains constant. Set it to the lowest ISO your camera allows, preferably 100 or less. That way, you know you've taken one variable out of the equation. Choose the best ISO for the situation (in this case, the lowest available), set it, and forget it.

If you can't set the ISO manually on your camera, keep an eye on it as you shoot. The LCD on your camera should show you what the ISO is while you're shooting. If you're shooting indoors, you may need to Increase your available light in order to keep the ISO from going above 100 (or the lowest setting available if that's higher than 100). An ISO of 100 would have been considered a "slow" film speed, so remember a low ISO works best when there is a lot of light available. Even with a lot of light, shutter speeds can be slow. This is why a tripod is essential. Don't try to hand-hold your product shots. If you can't buy a tripod, set the camera on a stable surface. If you have a variety of books or other stable, stackable objects, you can make fine adjustments to the camera's height using the books. For a little more height add some poetry, for a lot more height add a dictionary.

If you buy a full-size tripod, be sure to get one with a ball head so you can tilt and swivel it wherever you need to. Make sure it allows you to position the camera both vertically and horizontally when shooting. Small levels embedded in the head are nice, as is a reversible middle pole so you can shoot low to the floor if necessary. The legs should telescope to bring the camera close to eye level. You only want to extend the middle bar for small adjustments, because it is less stable when it is fully extended. Use the legs first to get you close to the right height, then the middle extender for fine adjustments. The tripod should be sturdy, but the lighter the better in case you want to travel or hike with it.

If you buy a small table-top tripod, make sure it will support the weight of your camera. If possible, test it with your camera before buying it. All of the features you want in a full-size tripod are also valuable in a table-top. The more adjustable and stable it is the better.

I think that's plenty to absorb for now, so I'm going to end this post here. I'd like to continue this first series on basic technology by talking about aperture and shutter speed, including a discussion of focus and depth of field. If people are interested I could do a blog on tripods. Otherwise, I'd like to talk about composition, and specifically composing for ArtFire's listing formats, then talk about lighting and props. Please let me know what you think in the comments, and feel free to ask questions.

Megan @ DalyCraftWorks


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  3. Okay. It's not that hard to post a link. LOL
    Here we go again! I hope this time I copied the correct code.

    first illustration
    second illustration

    The illustrations are not showing up for me, so I hope this helps!


  4. Wow! Such an informative post. I am going to have to grab my camera and come back and read it again. Every time I find something that talks about aperture, fstop and all that, I just glaze over. It actually helps to have the water and bucket analogy.

  5. Very informative, helpful and well written post! I can't wait for the next one! My pics are shot using an ISO of 80, which is as low as my camera will go. They are coming out very grainy though. Not enough light? Help!

  6. Hi, Tina. Happy St. Patrick's Day! An ISO of 80 is fine. If your ISO is set to stay at 80, then as you said, the problem may be elsewhere. Can you give me more info on your camera and editing process? Do the original shots look dark and/or grainy? Are you shooting in Raw or JPG? Are you lightening or enlarging them with software?

    If you'd like, you can email me a couple of the shots you find most problematic, via my AF studio link in the byline. If possible, send the files as they came straight off the camera, before post-processing. Thanks,

  7. Very informative! Thanks so much!