Photograph is a Hobby - The Lesson about Aperture of The Lens

Photograph is a Hobby

The Lesson about  Aperture of The Lens

Some of people have many different hobbies. Below, let me to share about my hobby,  It's a Photography...

General principle and implications for the depth of field.

1. Explanation of the basics of opening :

The aperture is one of three important parameters (with the speed and sensitivity) that manage exposure.

The opening is size of the area that will allow light to pass through the lens during exposure. 

(a hole formed by strips of metal, the size of which can be changed).

Aperture is expressed, by convention, with value f /, where:
a small value f / (. eg f/2.8) is an open letting in plenty of light, which is useful for low light scenes (prevents underexposure);

conversely, a great value f / (eg. f/11) is a small opening letting little light, which is useful for very bright scenes (avoiding over-exposure).

The most common aperture values ​​are:

f / 1.4, f / 2, f / 2.8, f / 4, f / 5.6, f / 8, f/11, f/16, f/22, f/32.

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Two examples of large and small depth of field (Figure 2):

two images on the left were made with a larger aperture (f/2.8) and a small depth of field

the two right images were made with a small aperture (f/16) and a large depth of field

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2. The opening practice :

In general, there are two main reasons for us to change the opening:

change the amount of light passing through the lens (eg, open the aperture up to let more light in order to use a fast speed.)

change the PDC (eg. shut up the diaphragm so that all plans are clear photo).

But one never goes without the other if you open to let in more light, you also decrease the PDC, if you close to increase the PDC, you decrease the amount of light passing through the lens ...

Thus, as often it will need to decide what is your priority and change other settings (usually the speed or sensitivity) to get what you want.

Finally, note that opening also has a slight impact on the optical performance of the lens, the end openings cause optical aberrations greater. Concrete and abstract:
Very large aperture (short of f/5.6, f / 4 or f/2.8, depending on the quality of the lens) generally cause vignetting (the corners of the image are darker than the center);

Very small openings (beyond f/16, for any purpose) causes diffraction (optical phenomenon that leads to a lesser sharpness / image quality).

Thus, in case you do not have special requirements related to the opening (for brightness or PDC), better to use an intermediate aperture (f/5.6, f / 8 or f/11) in order to get a better picture quality.

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3. Exercises to control the opening and depth of field :

To train you to use different apertures,  Chose the aperture priority mode on your camera, this mode allows you to select the desired aperture while the camera automatically adjust the other

At first, in order to simplify the task, made tests in favorable lighting conditions, such as outdoors, in order to have enough light you do not want préoccupper difficulties associated with the speed or sensitivity due to lack of light.
To test the impact of the opening of the depth of field (PDC), find simple subjects with a set of perspective quite marked (eg. A character with a distant background) and made several times with the same photo a different opening.

Make also vary the distance of focus.

On some SLR cameras, there is a test depth of field button, which allows you to preview (in the viewfinder of the camera) what is the depth of field. If your case has to test for depth of field button, do not hesitate to use it!
Finally, you can also spend a few moments to test the optical performance of your goal (or your goals) at the end openings (and different focal if it is a zoom).
For example, to evaluate the vignetting, take a picture of a uniform clear surface at full aperture and compare with a smaller aperture (look over the pictures to see if they are significantly darker full aperture).

Finally, I hope that you'll enjoy the short lessons, and enjoy your hobby, even you are not a pro..