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Exposure - should I try Manual or Semi Manual Exposure?


Camera manufacturers work hard to better automate their cameras. Always better Auto modes, Art filters, Sweep panoramas and the list continue. The problem is, the better it gets the further away we are from what happens inside the camera, when taking great images. I cannot help to think that the Mode Dial on most cameras never leave the A (Auto) position. Does it need to be on anything else than (A) in order to take good images you might ask? The answer is a BIG NO, great images does not only happen in manual or semi manual exposure mode. Photography in general has so many different sides to it that it will be incorrect to say that exposure is the only thing that will make or break a good photographer.

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That said, I personally believe a thorough understanding of exposure can help the photographer to be more creative, it will help the photographer to better plan an event or image and improve his or hers success rate during photo sessions. In this article I will discuss the basics of exposure. Similar to the other articles I wrote, it is important that you practice. Practice will build your own confidence and experience and most important you will master your camera.

In the two previous articles, Dynamic Range and White Balance, we discussed various technical and theoretical aspects of photography that are closely related to this article also. I therefore like to invite you to read those first.

I like you to paint the following picture in your mind. You have your new SLR camera with you and you taking a few casual images. As you lift the camera and as you look through the optical view finder of the SLR camera, the following happens. Light enters the front of the camera lens, goes through the lens, hit the mirror, get reflected through the pentaprism of the SLR optical view finder into your eye. As you press the shutter release button to record the image, the mirror moves up to free the image sensor, the shutter opens and instead of being reflected up to the pentaprism the signal now hit the sensor for the duration the shutter is open. If the shutter opening was opened wide enough plus if the shutter stayed opened just long enough to perfectly "expose" the sensor then we will have the perfect image.

Folks we just described what happens when we
expose the camera sensor. In the description two variables played an important role to get the right level of exposure, the diameter of the shutter opening plus the time the shutter stayed open. The ratio between the diameter of the shutter opening and the time the shutter stayed open determines how much light will hit the sensor. The time/diameter ratio we used in this example linked to the amount of light that hit the sensor can be defined as basic "exposure".

To complete the picture in your own mind you need to consider the following. It could happen that we opened the shutter and that the sensor was exposed perfectly, but the sensor was not switched on. Logical you would say, how can you expect me to take a picture if the sensor is not switched on. The sensor is an electronic component and different to the old film role, it needs to be switched on in order to function. Sensor manufacturers took this principle a step further by giving the photographer control over the switching on/off, off the sensor. To picture the "how much switch on" concept think of your living room lights that can be dimmed. Manufacturers gives us the option to switch on the camera sensor incrementally until its fully switched-on, or until it reaches its full sensitivity. In bright sunlight one can turn the sensitivity down and in a darker room one can turn the sensor sensitive up. The sensor sensitivity is adjusted with the ISO button on the camera. A high ISO value (ISO1600) means a high sensitivity and a low ISO setting (ISO100) means a lower sensitivity.

In the above described picture we referred to shutter opening, the time the shutter stayed open and finally we discussed sensor sensitivity. We therefore saw that three variables are responsible for correctly exposing the camera sensor. In photography we speak of Shutter Speed (time shutter stayed open) and Aperture (shutter opening) and ISO (sensor sensitivity).

When the concept exposure was developed the developers decided to implement a basic but standard practice that will be the same all over the world. This standard basically says that if the shutter speed is increased by a full stop then the light hitting the sensor will be halved. If the shutter speed is one full stop slower then the light hitting the sensor will be doubled. The same rule applies for the ISO setting and the Aperture settings. Be careful not to mix a half stop with a full stop. For example an aperture of f3,5 to f4,0 is not a full stop. Its also possible to increment or decrease the settings in third steps or half steps.

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Exposure therefor has three important variables, ISO setting, Shutter Speed and Shutter Opening or Aperture. These variables will determine the camera exposure. Below I show you graphical view of Aperture, plus you will see exposure expressed in a triangle to help you save the picture we build in your own mind.

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Light is therefore the basis for all our “exposure” decisions. How much light do we have? What is the quality of the available light? What intensity do I want? Do I need a flash? Do I want to add or subtract light? What do we mean by quality of light? It basically means the photographer will always qualify the light. If you out doing a photo shoot and the sky is hazy not giving a nice view on the surroundings then one typically say the light quality is not good. Late afternoon sun normally has better "light" quality than midday sun....

Then we also need to consider the "
scene effect" we want, should everything be in focus, do I need to freeze the moment, do I like to mimic movement, is it a candlelight scene? Each of the three exposure variables has specifics characteristics to help control what the "scene effect" will look like. The following are unique aspects of each of the three exposure variables, Shutter Speed, Aperture and ISO.

Shutter Speed - With shutter speed we can freeze a moment (fast shutter speed) or we can simulate movement (slow shutter speed). Shutter speed will also determine camera shake, we typically want to use a minimum of a 1/60th of a second with a 50mm focal length setting to prevent camera shake. With a 200 mm lens we will require a minimum shutter speed of 1/250th to prevent shake. If a stabilizer is good then one normally say it could give a 3 or 4 stop benefit. That means instead of a 1/250th on a 200 mm lens one would be able to use a shutter speed as low as 1/250th less one stop = 1/125th less one stop = 1/60th, without shake for a three stop gain.

Aperture - With the Aperture setting we can do a number of things. Aperture will determine the depth of field (what is in focus). With a large aperture one can do low available light photography (typically a concert). We refer to a lens with a large aperture setting of f2,0 or f2,8 as a “fast” lens or kit lenses are typically referred to as slow lenses because the lowest aperture setting they have is f3,5 or f4,0. Personally if I do not use Manual Mode much on my camera I prefer to use Aperture Priority Mode. I find Aperture Priority mode to give me the most creative control options.

ISO setting - ISO has no specific characteristic other than it creates grain at high ISO settings. Sometimes it can be of help to create specific old looking black and white scenes. Personally I use ISO to support the shutter speed or the aperture setting I want.

The above description of each exposure variable is only a small window into what each of them can contribute towards the specific scene effect you want. As you build your own confidence and experience you will see and learn about many more effects you can create. In the examples below I used the three exposure variables to create the scene effect I wanted at the right exposure level.

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Night


This a typical night scene. I found that night time aperture does not have the same visible effect as in daylight. In daylight I would typically use a smaller aperture (f8,0 - f14) to ensure the complete building is in focus. Using a smaller aperture as described in a night scene, I have to select really long shutter speeds which only increases the chances of camera shake. I therefor like to up the ISO (ISO800) a little to support getting the shutter speed (30 to 120 seconds) down and too select a moderate aperture (f5,5). The camera will be fitted to a tripod.

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Panning


This is a typical panning shot. To get the effect one first have to practice to move the camera in a smooth movement to follow the car. The shutter speed will be not really high because we do not want to freeze everything when we press the shutter release. The aim is to keep the shutter open just that moment longer to capture the moving effect. While doing this the panning movement must be steady enough so that the car is sharp. We only want to focus on the car which will normally require a large aperture of f,2,8 to f3,5. But in this case we want to bring down the shutter speed so we have to up the aperture to about f5,5. That will typically bring down the shutter speed to below 1/60th. Important is to keep the ISO at its base setting of ISO100. Taking up the ISO will only increase the shutter speed.

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Action


Here we want to capture the moment. Again we do not need a large depth of field. Using a aperture of f2,8 to f4,0 will give more than enough focus depth. Next is to get the shutter speed up in order to freeze the flag at the instant I press the shutter release. To do that I prefer a shutter speed of 1/500th or more. To support getting the shutter speed up I might have to increase the sensor sensitivity to ISO800.

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Movement


What do we need to do to create the movement in the image? This should be you first question when you plan a shot, how much focus do I want, is it a night scene, is it a portrait and so we can continue. Each type has a typical base setting one can work from plus each type has a lead exposure component. In this example Shutter Speed will be the lead component. To create this movement type effect we need to keep the shutter open a fraction longer. Again not too much because then all will be blurred. After deciding the shutter speed then the aperture and ISO will follow.

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Creative


As I mentioned elsewhere in this image, a good understanding of exposure, light and how to apply it will just open your creative mind. This is a basic example of how to create movement with rich colors. This can be used as is or it can be used as a overly for another image in Photoshop. I will leave the details for how to adjust the camera away from this description. I invite you to try it for yourself and to discuss it in the forum section with us.


Conclusion


Folks I hope you found this article interesting. I shared a lot of information and I will not be surprised if you need to read the article a few times. If you can arrange the different aspects I discussed in this article clearly in your mind you will experience photography totally different to before.

In this complete article I never talked about exposure compensation. The reason is simple. Those who advice you to use exposure compensation to control dynamic range or to correct camera problems should not be on your list of trusted advisors. Exposure as you saw is a complex topic and not something you quickly vary or alter with a exposure compensation setting. If you really believe your camera tends to over expose over the full scale from dark to bright scenes then I will agree to dial in a small compensation. On the other hand if it is exposure you want to control then my advice is to read the above article one more time.

The digital camera is a creative tool and in the right hands it can deliver wonderful results. The key to success is knowledge, practice and experience.

You welcome to mail me your images and those I really like I will display on the site.

Siegfried