Autofocus

February 15th, 2010 Andrei

This feature can be found in all digital cameras. In autofocus (AF) mode the camera will automatically focus on the subject in the focus area in the center of the LCD or viewfinder. Many digital cameras allows the user to also select other autofocus regions that will be indicated on the LCD/viewfinder.

AF Area

In “single AF” mode, the camera will focus when the shutter release button is pressed halfway. Some cameras offer “continuous AF” mode whereby the camera focuses continuously until you press the shutter release button halfway. This shortens the lag time, but reduces battery life. Normally a focus confirmation light will stop blinking once the subject in focus. Autofocus is usually based on detecting contrast and therefore works best on contrasty subjects and less well in low light conditions, in which case the use of an AF assist lamp is very useful. Some cameras also feature manual focus.

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AF Servo

February 13th, 2010 Andrei

This system allows the camera to maintain focus on subjects that are moving. It is a very useful feature for sports or wildlife photography and it is normally found on digital DSLRs.

Autofocus Servo is normally triggered by switching focus to “AI Servo” on Canon, or “Continuous” on Nikon, followed by half pressing the shutter release. The camera will continue to focus on the subject as long as the shutter release will be half pressed or fully depressed (actually taking shots). The Autofocus Servo usually also puts the camera into “release priority” mode so that the camera will take the shot when the shutter release is depressed, regardless of the current AF status.

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AF Assist Lamp

January 24th, 2010 Andrei

This is a lamp which is used to illuminate  the subject you are focusing on when shooting in low light conditions. The lamp is usually located beside or above the lens barrel. These lamps are not very powerful and they usually only work over a short range, up to about 4 meters. The light that they make is usually visible light, but there are lamps which uses infrared light instead. This is better for candid shots where you don’t want to startle the subject. Notable higher end external flash systems feature their own focus assist lamps with far greater range.

laserfocus

The picture above is a hologram AF found on some Sony cameras. This works by projecting a crossed laser pattern onto the subject. This bright laser pattern helps the camera’s contrast detect AF system to lock on to the subject. The system works well as long as the subject is large enough to be covered by several laser lines.

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AD Converter

January 17th, 2010 Andrei

Sensors from your digital camera consists of millions of pixels with photodiodes which convert the energy from the light (actually from the incoming phototns) into an electrical charge. That electrical charge is then converted to a voltage which is amplified to a higher level so that it can be further processed by the ADC (Analog to Digital Converter). In accordance with the voltage value, the ADC classifies it into a number of discrete levels of brightness and assigns each level a binary label (a number in binary code, consisting of 0 and 1). The ADCs are classified by the number bits that this labels are formed of. So a one bit ADC will classify the voltage as either 0 (black) or 1 (white). A two bit ADC would categorize it into four (2^2) groups (black-00; white-11; and two levels in between-01 and 10). Most consumer digital cameras use 8 bit ADCs, allowing up to 256 (2^8) distinct values for the brightness of a single pixel.

adc

The minimum resolution (bit rate) of an ADC is determined by the dynamic range (accuracy) of the sensor. For example if the dynamic range of the sensor is 1000:1 (or 60dB) the ADC must be at least 10 bits which is 2^10 = 1024 discrete levels. This will avoid loss of information. Theoretically a 10 bit ADC is the perfect fit for this dynamic range (1000:1), a 12 or 14 bit ADC will not generate additional tonal information other than noise. However, in practice it makes sense to overspecify the ADC to 12 bits to allow for some margin of error on the ADC.  It is also useful to have extra bits available to minimize posterization or banding when applying the tonal curve to the linear data.
Often, marketing material advertises the bit rate of the ADC to suggest the digital camera or scanner is able to output images with a high dynamic and tonal range. From the above it is easy to understand that this is only true if the sensor itself has sufficient dynamic range. The tonal range and dynamic range can never be larger than the dynamic range of the sensor.
Digital SLR cameras have sensors with a higher dynamic range and are usually equipped with 10 or 12 bit ADCs. Normally such cameras offer the option to save the 10 or 12 bits of data per pixel in RAW because JPEG only allows 8 bits of data per channel.

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Lesson 22: Conclusions

January 5th, 2010 Andrei

ConclusionsI will conclude this first beginner tutorial with some basic ideas that you need to have in mind when taking photos, so that you will be satisfied with the final result.

What goes through your mind in the moments as you raise your digital camera up to take a shot and before you press the shutter? If you’re like many digital photographers you’re not thinking about too much – you just want to capture the moment and then move on. However getting in the habit of asking some simple questions can help take your images to the next level. Here are some questions to get in the habit of asking while framing your shots.

What story am I telling? – This is an important question and one that should help you to make any number of decisions in terms of composition, framing, exposure etc. In essence what you’re asking is “why am I taking this shot? What is it’s purpose and what am I trying to convey?”

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Happy New Year

December 29th, 2009 Andrei

Happy New YearHello everyone! I’m on vacation right now and this is the reason why I haven’t post nothing new lately. So I just wanted to assure you that new lessons and many other interesting articles will come soon. Meantime I hope you all enjoy holidays and take as many beautiful pictures as you can! I wish you all a Happy New Year!

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Lesson 21: Background

December 13th, 2009 Andrei

BackgroundThe background in a photography is both an opportunities and a challenge to photographers. On the one hand it can put a subjects in context and make it stand out in a way that highlights it wonderfully, but on the other hand backgrounds can overwhelm subjects and distract from them. Some of the common problems that photographers have with backgrounds are:

Distracting Focal Points – this can happen to everyone – you line up a shot of a friend to take a portrait and just as you press the shutter someone else pops into the frame with the intention of ruin your shot. The result is that the real focal point of the shot becomes this person which pops into the frame. This is an extreme example of distracting focal points in the background but it’s something that happens quite a lot.

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Lesson 20: Active Space

November 26th, 2009 Andrei

20Shooting moving subjects is always a challenge. The time is short and usually you don’t have a second chance, so you must think and act fast. One of the most important rule that you’ll have to consider when shooting moving subjects is to give them space to ‘move into’. The main idea behind this is to frame in that way so the subject will have space in front of it. Some call the space in front of a moving subject the ‘active space’ in a photograph. Alternatively the space behind your subject is often called ‘dead space’.

The reason that this compositional technique is used is that when someone views an image and sees that your subject is moving in a direction, their eye naturally moves in that direction too. It’s something instinctive. Working with the way your viewer will instinctively view your image helps to create balance, drama and anticipation in your shot.

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Lesson 19: Using Focal Points

November 22nd, 2009 Andrei

16Next time when you are about to press the shutter button on your camera, take a moment and ask yourself: “What is the focal point in this picture?” Some other ways to ask the same question might include – What is the central point of interest? What will draw the eye of the viewers of this picture? What in this image will make it stand out from others? What is my subject?

The reason a focal point is important is that when you look at an image your eye will generally need a point of interest or something that will really hold attention. Without it you’ll find people will simply glance at your shots and then move on to the next one. Once you’ve identified a point of interest or focal point you then should ask yourself how you can enhance it.

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Lesson 18: Filling Frame

November 15th, 2009 Andrei

Filling FrameThere is a rule in photography that says if you want to improve your photographs 100 percent, move closer. It’s true. The one sure way to keep from including too much extraneous information in a photograph is to fill the frame with your subject and nothing but your subject. Filling the frame from edge to edge leaves little doubt about what your intended target was. There are two ways to get closer: Use a telephoto lens or walk closer to the subject.

While empty spaces can be used effectively in photos to create stunning results you’re much more likely to get a positive appreciation from those looking at your photos if your shots are filled with interest. This technique is particularly important when taking pictures of people whose facial features tend to disappear when you move away from them.

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