Tuesday, 11 March 2008

Aperture Values

How to Use Aperture to get better Macro Photographs
The dictionary definition of an aperture is a hole or a gap. In photography the aperture is a variable opening that allows light to enter the camera. This means that you can control the amount of light that enters the camera by adjusting the aperture value. Aperture settings are calibrated or measured in f/numbers also known as "stops". Light enters the camera through the lens and finds its way to the film or digital camera sensor. When you adjust the aperture on your camera you are actually controlling movable blades (sometimes called a diaphragm) within the lens. Aperture is often the cause of confusion for beginners because the scale is written in reverse order. A large aperture of f2.8 would open the blades and make a larger hole. A small aperture of f22 would close the blades making the hole smaller. Take a look at the simplified illustration of aperture values in figure 1. Note that some camera lenses will operate at larger or smaller aperture values than in this example.

Figure 1. Simplified Illustration of Aperture Values (click to enlarge). This illustration is not to scale.

Understanding Aperture Values (Av) is an important step towards improving your macro photography. Below is quick summary of what we have learned about aperture so far.

  1. Aperture means small hole or gap and in photography it controls how much light enters the camera through the lens.
  2. Aperture is measured in f/numbers or stops
  3. Try to remember it as a scale – the lowest number represents the largest aperture and the highest number represents the smallest aperture.

If you have not found a way to memorise this summary I suggest you copy it down, take it your nearest tattoo parlour and have them tattoo this on the inside of your eyelids. This is possibly the single most important law of macro photography to learn.

Aperture and Macro Photography
Knowing how to control the aperture value is very important when it comes to taking macro photographs. I would recommend setting the camera to “Aperture Priority” mode, this will be marked Av or A on your camera. In this mode you can select an aperture value and the camera will select an appropriate shutter speed. This will enable the camera to take a picture with the correct exposure. The correct exposure means that when the picture is developed, viewed or printed the colours will look true to life. A picture that is too dark is under exposed and a picture that is too light is over exposed. This once again comes down to how much light has entered the camera. Too much light and the image will be over exposed and too little light the image will be under exposed. There are lots of elements that make up a good macro photograph. Exposure is another subject that requires a full introductory tutorial of its own! In simple terms the shutter speed controls the duration of the exposure. Although it is called shutter speed it actually refers to the duration of time that the shutter remains open. It follows that when you reduce the amount of light that can access the camera, longer shutter speeds are required. This allows the camera to collect enough light to create a properly exposed image. It should be starting to dawn on you by now that everything in photography is linked to the availability of light.

Fast Camera Lenses
A digital SLR camera body "knows" the minimum and maximum aperture of the lens attached to it. The camera will not allow you to enter an aperture value outside these figures. Once you understand aperture and how it will affect your photography you can use this knowledge when choosing a new macro lens. Unless you understand the f/number scale you will not realise the limitations or benefits that one lens may have over another. Luckily I have explained all this to you and now you can buy a new macro lens and understand how it will work on your camera! When photographers refer to a lens as being “fast” they do not mean it will auto-focus quickly. What they are describing is the large aperture size which will allow the lens to operate in low light conditions. This can be very beneficial in macro photography and this attribute is sort after in macro lenses.

I know that starting out in macro photography can be a daunting task. I say this quite often but macro is such a fascinating form of photography that you feel compelled to succeed. Provided that you follow my guidelines your macro photography will start to improve quite dramatically. I am confident about this because knowing how your actions affect the results will vastly improve your confidence. Just knowing this information about the aperture will give you much more control over the camera. At the end of the day a camera is a piece of equipment like any other and once you have mastered the controls taking macro shots will become second nature.

Use a Tripod
To accommodate for longer exposure times and small aperture values a tripod is generally required. A tripod will reduce the chances of your photographic work suffering from camera shake. A sturdy tripod is a not just useful during the shot, it holds your camera for you while you are working, leaving your hands free. I read recently that one photographer enjoyed the fact that his tripod made him slow down and compose his photographs more thoughtfully. This is a good point and not something I had really considered before. Using a tripod is a great for getting your camera where you want it. When photographing wild flowers this can be a real challenge. Often more time is spent on the set-up than actually taking the shots! It can take a long time in some cases to get the set-up and light how you want it. If at the end of the day you get the “money shot” than it will be all worthwhile. Setting up the camera and tripod is part and parcel of the process and will pay off once you get the hang of it. I have found that wild flowers can be difficult to photograph from above. I now always try to take a side view and then gradually move further outwards. I Always take several shots in the same position before moving the camera. This increases the chance of getting a good shot if one of the images is spoiled by camera shake or a sudden gust of wind.

Figure 2. Illustration of LCD display - highlighting Aperture Setting of f2.8

Looking at the illustration of the camera LCD screen, an aperture value of f2.8 is being displayed. The camera is being used in “aperture priority” mode. This means that the aperture value is entered into the camera manually. The camera will automatically select an appropriate shutter speed. When the shutter button is depressed half way the shutter speed will be calculated from the amount of available light. This tends to work quite well although there is no guarantee that the settings will produce an adequate exposure. Sometimes the camera will get it wrong due to the fact that light reflects from some surfaces differently than others.

TTL Flash
TTL flash operates through the camera taking into account your aperture value, shutter speed and ISO speed. A non-TTL flash uses its own metering system. I would recommend a TTL flash for beginners to macro photography. Most flash guns and macro ring lites are TTL compatible. A popular choice for insect or bug photography is to attach a flash gun to a bracket and then diffuse the light. This means to make the light less intense by placing a cover over the flash. This will let less light through when the flash operates. Depending on the operating mode, the camera will akes into account whether or not flash will be used when the shutter is activated. Flash is important in macro photography, even in good light it enhances the picture by picking out the details in the subject. The fact is that if you are serious about macro photography you will need to get a decent flash system so that you can use faster shutter speeds. Long exposures and large apertures make macro photography very difficult as proved in my last post. At this stage I have established all the basics facts about aperture values.

Depth of Field!
In my next post I will be covering Depth of Field (DOF). This is controlled using the aperture so it should follow on quite well from this post. I realise that getting started in macro photography can be frustrating and difficult. It is quite important that you try to get all the equipment necessary to take a good macro picture. If you can not afford to get new digital SLR equipment have a look for some second hand gear. Most photographers take great care of their gear leaving it in tip-top condition. Another option is to have a look at the bridge or compact cameras. I have seen some very good macro photography taken with these cameras in recent years. Unfortunately photography is an expensive occupation. There are lots of websites that claim that you can make cheap equipment and get good results. This is partially true, but you generally need to invest in some good camera equipment if you want to get consistently good macro images. It is better to learn how to do this properly with good equipment so that you are not missing good photographic opportunities. In my next post (as stated above) I will explain how aperture can be used to control the depth of field.

I hope that this has been a useful source of information for you. If you have any questions, queries, concerns or comments about this article or website please feel free to contact me. Thank you for visiting and reading my Macro Photography for Beginners website.

Marvin Africa

1 comment:

Anonymous said...

Hey nice articles - best info. so far on macro....Do keep on adding!