LESSON: Focusing

Camera lens focused on the droplets

    Okay, you see that shutter button on your camera? Or that button where you click so that it can capture images? Well, that is an important feature in most digital cameras nowadays. That button is also like the focus button for the camera lens. Well, that's only applicable when the camera is in AF (Auto Focus) mode. For convention, please set your camera to AF mode this time. We're gonna need it for our focusing lesson. We will tackle manual focusing as we progress through the lessons.

HOW TO PROPERLY FOCUS USING AUTO FOCUS MODE

Below is the image of a camera button.

Unpressed shutter button

   There are two levels for that shutter button. The first level is when you lightly apply force on your fingers just enough to sink the button without fully pressing it. One must press the button down enough to a point where you feel a greater resistance to your finger. That first level is the auto focusing trigger. It will automatically focus to the entity that the camera's sensors can detect. That focus button is very important for capturing images especially if you want to take pictures of nearby objects. The figure portraying the lightly pressed shutter button is shown below.

Half-press or slightly pressed button for focusing

       The greater resistance that you feel after pressing the button lightly is the second level of, where the camera would capture the image, and store it in its electronic memory storage. This is sometimes accompanied by a small 'click' feeling when you press the button. The figure portraying the fully pressed button is shown below.

Fully pressed button. This will capture the image

IMPORTANT: 

Always keep in mind that before completely pressing the shutter button, one must first lightly or halfway press the shutter button for the camera to fix its focus on the entity. 

The camera will indicate whether it has reached focus or not. It is like locking on to the target.

One must first lock on to the target or entity by focusing, and after the camera achieved proper focus, then it is the time when the photographer must fully press the capture image button.

      A proper focus is usually indicated by a small green circle on the camera's display. An improper focus is usually indicated by a blinking red circle on the camera's display. Sometimes, the camera would just make audible 'beeps' or sound pulses. Usually, a greater number of pulses indicates that the camera didn't achieve proper focus, and a smaller number of beeps indicates that the camera achieved proper focus.

The camera was not able to focus properly. A blinking red circle indicator will be displayed on the screen of the camera. Sometimes, the camera would just 'beep' or create multiple sound pulses that the user can hear. These beeps will indicate if the camera achieved focus or not.

A proper focus was achieved by the camera. A green indicator is usually displayed in the camera's display. If not, a small number of audible beeps will be heard.

   

     AF focusing makes life easier in most cases. The camera will automatically focus on the subject depending on the camera's sensor readings. The technical part of this will be discussed below.

AF focusing is truly useful on entities that are near the camera. It can soothe the pain of manually focusing the lens of the camera to a desired point.

auto focusing done by the camera

Image captured using auto focus mode.

 MANUAL FOCUSING

  There are some lenses in SLR (Single Lens Reflex) cameras that don't have AF mode. These lenses require manual focusing. Manual focusing is mechanically done on the lens. It usually requires twisting a part of the lens to change the focus. 

Manual Focusing done in macro mode

In some lenses with large focal lengths, autofocus is not included. This is due to the imperfections of autofocus in long distances. This will be explained below.

HOW A DIGITAL CAMERA OPERATES ITS AUTO FOCUS MECHANISM.

     The camera emits a light to the entity. For most cameras, this light can't be seen by our eyes. That light will be reflected by the entity back to the camera. The light sensor on the camera detects  how much light packets go back to the sensor. These factors determine the distance of the entity is to the camera. The camera, based upon the sensor data, it will try to mechanically drive the lens to focus on that distance.

The camera emits a light ray displayed by the red line. The blue box is the entity. As the light ray hits the entity, some of the light reflects back to the camera's sensor

   I told you earlier that the AF mode of the camera isn't effective in large focal length  lenses. The entity you are trying to shoot is really far away in these cases, and only very small packets of light are emitted by the object. These small packets of light cannot be detected by the camera sensor.

    The distance between the entity and the camera can make the emitted light vulnerable to distortions. These can be due to the environment, when there's too much fog, or the color of the entity is black, where it absorbs much light, light bending due to varying densities of the air, etc. The emitted light can only reach the subject, with only a fraction of its total amount because this light is distorted when it reaches the subject. When this travels back, this emitted light has a high possibility of not reaching the sensor of the camera. Thus, the camera can't figure out the distance of the entity from the camera, and this will render an improper focus by the camera. In these cases, manual focusing is needed.

Pictures involving imperfect autofocus in long distances:

Auto focus was set here, but unfortunately, the camera cannot focus on the entity using auto focus mode.

auto focus imperfection. The auto focus cannot detect the entity. This gave an unfocused image.

      Manual focusing is also an advantage when times are needed. Auto focusing is not reliable in long distance shooting. Manual shooting is needed in these hard situations. 

Manually focused lens. This time, the entity is clear and sharp.

NOTE: The camera can't read your mind. So the camera doesn't know where you want to focus. The camera relies on its software and sensors to achieve an accurate focus. 

On manual focusing, specifically in DSLRs, there are lenses that display a range of its attainable focus points. These foci range is marked on a part of the lens. These marking can be in meters or in feet. 

Source: http://www.123rf.com/photo_2407980_the-markings-on-the-barrel-of-a-1980s-manual-focus-wide-angle-camera-lens-showing-aperture-distance-.html

The lens has markings on where to place its focus on.

BASIC EXAMPLES IN FOCUSING

      Assuming that a subject lies 3 meters from the lens, and the subject's background is the forest (it is always assumed that far away subjects have infinity distance) and a part of its foreground (1 meter from the lens) are pebbles. 

The photographer marks his/her focus on 3 meters. Now, the lens is focused on the subject (the subject is clear, both background and foreground are unfocused),  

but when the photographer extends the focus to infinity, the subject and the foreground become unfocused, and the background, which is the forest becomes focused.  

The photographer sets the focus of the lens to 1 meter. The foreground gets focused, and the background and subject are unfocused.

Usually, the unfocused subject is blurred due to some optics princples that we won't tackle for now.

TIPS: 

-In auto focus mode, common in most digital cameras, do not immediately press down the shutter button. Always take time to focus on your entity by slightly or pressing the capture image button halfway.

-When shooting far away or very near from an entity, first try the auto focus mode. If it is  effective, it will give a nice and accurate image, but if you're uncomfortable with using auto focus due to inaccuracies of focusing,  delay time of focusing, unable to focus properly, you can always switch to manual focusing.

-Setting a lower f-stop number will make the unfocused part more blurred. A nice type of blurness is called "Bokeh". You can search it up the net what it really means, but for now it's a japanese word that's being used in photography to define a blurness that is distinct and nice.