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Lens Aperture – What it Is, Does and How to Use it
Aug 7th
The lens aperture is a measure of how much light the lens will let through into the sensor in the camera body. The bigger the aperture is, the more light will shine through. Using a bigger aperture also results in less depth of field (depth of focus, DOF). If it’s difficult for you to remember, just think of the small, pocket-sized digital cameras you can get nowadays. They tend to render everything in focus opposed to the more sturdy, professional single-lens-reflex (SLR) cameras that have the ability to create soft, out-of-focus (OOF) areas behind the main subject. Big means plenty of light-sensitivity together with a narrow focus area.
The aperture is measured in terms of f-stops and this can perhaps be a bit confusing since a smaller f-stop is equivalent to a larger aperture. It is usually written like this, the scale going from large aperture to small aperture:
f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16…
These are the standard values, separated by one unit called an f-stop. Each lens has a maximum aperture and can be stopped down from there to gain larger depth of field and to set the exposure (which it does together with the shutter and ISO speed). Another good reason to stop down your lens (to use a smaller aperture) is that the lens usually works better when stopped down 2 to 4 stops from it’s maximum value. It draws sharper and lessens unwanted effects such as chromatic aberration and vignetting. Using a lens wide-open so to say, is rarely a good idea unless you are pressed for light or using an absolute top-of-the-line lens.
A fast lens, you say?
Sometimes the large-aperture lenses are also referred to by photographers as ‘fast lenses’. Strictly speaking this is nonsense since it’s still a piece of glass and not a racing car! But what it means is that with a large aperture, more light will come in allowing for a faster shutter time in the camera. The lens itself is in no way ‘fast’, it’s just easier to say that ‘the lens is fast’.
With a ‘fast lens’, you can use a high shutter speed, ie. in the thousandths, 1/1000 sec or less. This allows you to really capture moments that’s gone in the blink of an eye and opens up a new world of things that happen too quickly for the human eye to catch.
As is now evident, the depth of field is directly related to the lens aperture. Having one of these ‘fast lenses’ on your D-SLR camera gives you lot’s of creative possibilities. One of the big challenges in serious photography is to separate your main subject from all the background clutter, to focus the viewers attention on the subject without distractions. To get a blurry background, set the aperture quite high, go a little close to your subject (without exaggerating the perspective too much) and allow some distance between your subject and the background. It’s important to remember that the placement of you, your subject and the background also plays a role in how much blur-effect you get. It’s not only about what lens aperture you are using.
Bokeh
Ok, so now you have an out-of-focus background. But there’s a bit more to it than that. (Admittedly, we are moving into the subtler details now.) If you look at the out-of-focus areas of different photos, you’ll see that it can look quite different. Some lenses have a really nice, soft, smooth and silky way of rendering the out-of-focus details while others have a tendency to render hard rings and edges around high-contrast objects. This can be a bit distracting to look at although it is somewhat subjective. The quality of the out-of-focus areas is generally called ‘bokeh’ and is largely decided by the way the lens is constructed, how many aperture blades it has and what f-stop you are using. Photo aficionados can debate at length about the quality, characteristics and effects the bokeh has on a photo while more ‘normal’ people would give far more importance to the focused areas of the photo. In some genres though, it does play a significant role. In portrait photography, wildlife photography (using long tele-photo lenses) and macro photography the silky bokeh can really be the dot that makes the ‘i’, an add a magical touch that’s hard to pin down.
Try to incorporate some bokeh awareness into your photography and there’s most likely improvements to me made.
Digital Photography: Aperture Priority, Shutter Priority, and Manual Modes
Jul 16th
Digital photography has given almost anyone with a camera the potential to become a creative photographer. These days even compact cameras offer features that once were only found on ’serious’ SLR cameras.
The trouble is, most people who have grown up with point-and-shoot cameras have very little idea what these features are all about. After buying a good digital camera with the best intentions, they soon give up and switch to automatic.
Are the settings on your camera really so hard to understand? Of course not, but it can seem that way at the start, especially if they are not explained to you in simple terms you can understand.
The two settings you need to understand here are Aperture and Shutter Speed. Aperture is the size of the hole that lets the light in for your photo. The larger the hole, the brighter the exposure. The shutter speed is the length of time given to each exposure. Slower shutter speeds allow more light, resulting in a brighter exposure. By finding the right balance of these two settings, you and/or your camera control whether your photo is overexposed, underexposed, or just right.
With your camera set to Manual mode, you control both settings. If this seems daunting, you can start with the semi-automatic functions, Aperture Priority and Shutter Priority.
How do the semi-automatic functions work? They allow you to choose one setting (either aperture or shutter speed), while the camera chooses the other. That way you can be a little bit creative, but with the safety net of knowing your camera will make sure your exposure is correct. It is a good halfway point between automatic and manual.
Let’s start with Aperture Priority. This function allows you to set the aperture on your camera; the camera chooses the shutter speed for you.
The aperture controls depth of field (the area in front and behind the main subject that will be in focus). When you set a wide aperture, you reduce the depth of field; when you choose a smaller aperture, you will have a greater depth of field.
Obviously when you change the aperture, you change the level of light in your exposure. The camera will compensate by adjusting the shutter speed. So when you operate your camera in Aperture Priority mode, you have control over the depth of field, but your camera still makes sure your exposure is correct.
The catch here is, you still need to keep track of what your shutter speed is doing. If it falls to a very slow speed, you need to use a tripod to eliminate camera vibrations.
How about Shutter Priority? Here you set the shutter speed, and the camera balances the exposure by setting the aperture. This is a great system if you are working with moving subjects. Sometimes you may want to freeze a moving subject with a fast shutter speed, or create a motion effect with a slower shutter speed. Meanwhile the camera compensates for the changes in shutter speed by adjusting the aperture.
Shutter priority may be a better option for some beginners. It is much easier to stay aware of when to use your tripod. Also, when your camera manages the aperture, it controls the depth of field, which is not usually as critical as the shutter speed. You may not always get exactly what you want, but you won’t get any catastrophic failures.
These two semi-automatic functions appear to offer you the best of both worlds. You get to be a bit creative, and try out your photography skills, while your camera’s high-tech hardware makes sure you don’t overexpose or underexpose the photo. So far, it sounds perfect.
So why should you learn to operate your camera in Manual mode? The answer is simple.
Aperture Priority and Shutter Priority both work on the assumption that your camera’s reading of the exposure is always correct. Unfortunately, that is not always true. In fact, sometimes you have to be smarter than your camera.
Imagine you are photographing a flower in the sun, but the background is in the shade. This simple situation can be all it takes to confuse your camera. It may expose for the background, brightening the exposure and totally overexposing the flower.
In this situation, semi-automatic settings will not solve the problem. You could try to darken the exposure by (for example) closing the aperture. The camera would simply adjust the shutter speed to compensate, maintaining what it believes to be the correct exposure.
What you need to do is switch the camera to Manual. Then you can adjust both settings and create an image that is slightly darker, bringing your flowers into perfect exposure.
This is not just a hypothetical exercise. Situations arise all the time that require you to out-think your camera. If you understand how to operate your manual settings, you can take control, and you won’t be left blaming your camera for ‘the one that got away.’
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