Photography Basic

Photography course – Basic

The world of photography contains many terms that we may not be familiar with, out of our everyday living, and we need to learn how to use them in order to fulfill the potential of photography. In this article, I will explain many of these terms and will describe (briefly) how they relate to the photos we shoot. I hope you'll enjoy and learn.


The Camera

Body – the camera's body is one of the few parts that's really hard to get along without. It holds all the essential parts and protects them from harm's way and other stuff like hits, moisture, drops etc. We can find plastic bodies and metal bodies, the plastic ones are lighter and usually cheaper, while the metal bodies are more durable, professional and expensive. The metallic alloys that make the skeleton of the body are usually magnesium, aluminum and other light metals – the choice of which determines the price tag.

Shutter – while shut, the shutter prevents the light from reaching the camera’s sensor, and dictates the length of time during which it reaches the sensor, while it's open. There are horizontal, vertical and aperture-combined shutters, the latter usually found in cheap compact cameras. The shutter is produced of light and durable materials and is meant to last for tens of thousands of cycles. When it's worn out it needs to be replaced. The shutter speed varies from 1/8,000 of a second in the more professional cameras, to 1/4,000 in the entry-level DSLRs, and 1/2,000 in the compact cameras, and for as long as 15 seconds, 30 seconds and even 'bulb' mode, in which the shutter is left open until told otherwise and can hold exposures of few minutes. Fast shutter speeds will "freeze" the motion in the frame, and slow shutter speeds will smear the motion. The guideline for avoiding blurry photos due to shaking hands is to use shutter speed higher than 1/(focal length); for example: if the focal length is 200mm, use shutter speeds of at least 1/200 to avoid smears.

Mirror – it's not to show how pretty you are, but to reflect the light which enters the lens upwards, where it enters a prism or a mirror system and exits into the viewfinder. The method in which the mirror system works strongly affects the brightness and other factors of the resulting image. The mirror system reflects the light through a semi-transparent mirror into two other sensors – the focus sensor (see focus) and the light metering sensor (see light-metering). When the shutter release button is pressed and the photography process takes action, the mirror lifts up, the shutter fully exposes the sensor, exposure occurs, and then the shutter closes and the mirror drops down. This process, in which the mirror is up and there is no light going through the viewfinder, is called Viewfinder Blackout, and it is critical in DSLR since the longer it is, the harder it gets to track objects in motion.

The Viewfinder – we already mentioned that light enters the lens and, by going through a set of mirrors, it eventually reaches the viewfinder. The main parameters regarding the viewfinder are its size, the magnification and the frame coverage. The size of the viewfinder says a lot about how comfortable it is, and of course – the larger it is – the easier it gets to take a look. The magnification factor implements the size of the projected image in the viewfinder, and the frame coverage suggests about how much of the frame is visible in the viewfinder (usually between 91%-100%). While looking through the viewfinder, we can find important information about the exposure, the scene, focus and pretty much everything we need to know (well, almost). Bear in mind that the distance from the viewfinder to the lens is exactly the same distance as the lens from the sensor, due to the fact that both need to be in exact focus. Compact cameras (not DSLR) use two main types of viewfinders: the optical VF (viewfinder) and the electronic VF or EVF. The optical VF uses a separate window and lens system to simulate the image received at the sensor, and it's main drawback is that there is some difference between the image in the viewfinder and that on the sensor because of the two different angles observing the scene. The Electronic ViewFinder (EVF) is, in fact, a mini-LCD screen inside the viewfinder; its disadvantages are that usually suffers from low resolution and that it lags behind the actual scene. Given these drawbacks, why use them on compact cameras? Good question; mainly because it saves the battery and some screens don't work as well in broad daylight. Tip: some viewfinders have diopter adjustments for those of us who wear glasses.

Bionet – that's the ring on the body of DSLR cameras into which we attach the lens. It is almost always made of metal and its job is to keep the lens tight on the body and to transmit, via electric contacts, information from the camera to the lens and backwards – regarding focus, aperture etc and provides electricity. The bionet also shifts torque from the camera to the lenses without an internal motor.

Flash – its job is to illuminate the subject under low light conditions or as fill flash to weaken shadows. It's recommended that you use external flash, which fits on the "hot-shoe" on top of the camera. The hot shoe holds the flash and transmits information from the camera to the flash regarding exposure. for further info read the Flash Photography article.

Assist light – under dim light conditions and total darkness, the focus system needs some help illuminating the subject for focus. Some assist lights use an ordinary white light, some use a pattern and some project a grid on the subject. All flash units assist the focus using a red grid. Some cameras also use the assist light to reduce the "red-eye" effect.

Batteries – what can you do, digital cameras need electricity and they are demanding. The DSLR cameras and the more advanced compact cameras use Lithium-Ion batteries and the cheaper compact cameras use AA rechargeable batteries. Today Ni-MH batteries are the best AA on the market and hold more than 2,700 mAh of juice, more than ever before. And the chargers have reduced the charging times from several hours in the past to even less than an hour for a full charge (!) Battery life is affected by the amount of photos taken, usage of the LCD screen, usage of flash, etc. By using the camera correctly you can squeeze more shots from each pack.

LCD – that tiny screen at the back of your camera is one of the greatest revolutions of digital photography. LCD stands for Liquid Crystal Display, and today they provide excellent viewing quality with rich colors and low power consumption. The screen is used both for building a composition and reviewing the image after the shot was taken. Turning the screen off will save batteries when needed.

Light Meter – all cameras today contain a light meter, unlike in very old cameras. The light meter is a sensor that meters the amount of light which enters through the lens and onto the sensor, using various method: Matrix – covering the entire frame; Center weighted – which gives 90% importance to the center of the frame and 10% to the rest ; Spot Metering – which meters only from the tiny spot in the center of the frame. There are several kinds of sensors: from simple grey levels to the 1,005 pixels RGB sensor found in Nikon cameras.

The Digital system

Digital photography introduced a system that never before existed in the world of film photography with many advantages such as practically endless photo number, immediate feedback on the photo taken, and lately even higher quality than film based cameras. in this part we will walk through the digital system and understand its parts.

The Sensor – That's actually our "film". Its job is to capture light and convert it from photons (light particles) into electrons by photoelectric cells. Each cell in the matrix transfers electrons depending on the amount of light that enters it. A proper analogy is buckets filling up with rain water (buckets being the sensor and rain is photons), each cell has a maximum capacity of "water" and if it fills up the pixel is white and can also affect the cells around it, and this effect is called "blooming". In modern sensor we can find a "drain" system that helps prevent this phenomenon.

The size of the sensor – size does matter. The bigger the sensor per given resolution, the larger surface area each photoelectric cell (pixel) is given, which eventually means each cell can gather more photons with less interference from other cells. This mainly means less "noise" in the image. A smaller sensor also requires a higher lens resolution since the pixels are smaller and denser. Another thing affected by sensor size is the Depth of Field, a smaller sensor means Greater DOF and larger sensor is shallower DOF. Smaller sensor also has a "crop factor multiplier" because it has a smaller surface than a 35mm camera film, it takes a small portion of the projected image (crops the image) and produces a normal frame, hence practically is multiplying the focal length covrage, for example Nikon DSLR has a X1.5 crop factor and Canon DSLRs have X1.6 crop factor And 50mm lens on a DSLR will produce similar frame coverage as 75mm lens on film.

CMOS – Complementary Metal Oxide Semiconductor – now that's a long name… in short, CMOS were originally used in computer chips, it's much cheaper to produce and the main difference between CMOS and CCD is that in CMOS each photodiode (pixel) holds several transistors that read and amplify the signal. Because light also hits these transistors and not only the photoelectric cells, these sensor are traditionally less sensitive to light. (I suggest describing CMOS before CCD)

CCD – Charge-Coupled Device – one of the two common types of sensors. In CCD sensors, the photoelectric cells on the sensor don’t have a designated transistor, but rather deliver the electrons flow to the side of the sensor, where circuitry surrounding the sensor processes the output and sends it to an A/D converter. CCD sensors produce high image quality, yet are more expensive to manufacture and consume more energy than CMOS. CCDs are more common than CMOS sensors.

ISO – International Standard Organization a.k.a. ASA American Standard Association. The sensor's sensitivity is actually the amount of amplification of the signal from the sensor. Every sensor has a base sensitivity in which it provides the 'cleanest' photo, and each increase in that sensitivity will shorten the exposure and produce a noise side affect. In low light conditions it's recommended to use higher ISO, but in general lower ISO is recommended for avoiding this "noise".

Electronic Shutter – we've already talked about regular shutters, now we'll talk about the electronic one. Some cameras only posses a mechanic shutter, some only an electronic shutter and some have both. Electronic shutter defines the length of exposure by stopping the readout from the photoelectric cells after the specified period of time.

Noise – just as there are interferences when we listen to the radio, there are interferences in digital photography. In the sensor, as we amplify slightly the sensor's signal in low ISO, we will find an image clean of noise. But as we raise the ISO, more aggressive amplification is occurring and static interference between the photoelectric cells is also amplified, producing random pixels in different colors. It's recommended to shoot bright images in high ISO in order to reduce noise visibility. Another kind of noise is produced in long exposure shots, which is due to sensor heating. Try avoiding long exposures that produce this noise by taking several shorter exposures and stitching them together via software.

Noise Reduction – every camera applies some sort of noise reduction. On the computer you can use software such as Noise, Ninja, or Neat Image to clean this noise. In long exposure shots, you may apply the camera’s noise reduction method, entitled "dark image subtraction" – in which the camera takes another frame after the original frame, this time with a closed shutter (resulting in a dark frame), and then reduces the "hot pixel" in the dark frame from the original one.

A/D Converter – we mentioned that the sensor receives photons and emits electrons in reaction, but the processor in the camera doesn't know how to read this information and that's why we have the A/D converter which reads the voltage output for each pixel from the sensor and attaches a value between 0 and 255 (in case of 8 bitcolor depth) and then gives it a binary sequence so that the CPU can process it. In 8 bit depth, 0 is black and 255 is totally white. In 12 bit system the pixel is given a value between 0 and 4096 (2^12) , resulting in a greater dynamic range and more details in mid-levels.

Color – as we said – each cell can distinguish 256 levels of brightness, so how does color get into the picture? By using a Color Filter Array of RGBG (Red-Green-Blue-Green) we have a quarter of the pixels red, a quarter blue and half of them are green. The reason for that is because the human eye has different sensitivity for each color. After the readout, an interpolation called Bayer's interpolation, is being done in the processor, which cleverly calculates the colors for each pixel in consideration with its surrounding pixels, This creates a 24-bit color-depth image (2^8 x 2^8 x 2^8 = 2^24). A different kind of color rendering is the Foveon way, which uses three different layers of color for each pixel in the sensor thus creating the most reliable color.

Buffer – after the image is created, it is stored in a temporary memory section called "buffer" until it has finished its processing and is written to the memory card. The size and efficiency of the buffer affects the speed of photography and how many photos can be taken before we need to wait for the camera to take the following shot.

The Processor – one the most important parts of the digital camera. The manufacturers invest many resources in developing the main image processor and the software that creates the image and determines the final image quality. These processors are very powerful and can process tens of millions of pixels a second.

Memory Cards – at the end of the photography process, the image is saved on a flash memory card. It's very durable and very small and can hold thousands of photos (on an 8 GB card for example). The speed of the card determines how fast the buffer will empty itself and shortens the delay between each photo.

The Lens System

as we learned in the previous two episodes, the camera is a very complicated device, but it is nothing without a good lens. The lens enters the focused light into the camera's body and onto the sensor. In this part we'll walk through the lens system and its parts.

Lens system – a lens is only one optical element and a combination of more than one creates a system. The purpose of the lens system is to determine the focal length, amount of light and the focus of the light on the sensor's plane.

Aperture – the aperture is a diaphragm; its main purpose is to determine the amount of light that enters the camera. The aperture consists of a number of overlapping blades, which determine the opening of the aperture, much like the iris in the human eye. The aperture values are a result of a simple equation that means the "amount of time the aperture diameter enters in the focal length" or F/x=focal length/aperture diameter. And so a 200mm focal length lens and an aperture diameter of 50mm will result in an F/4 aperture opening. So the bigger the aperture's diameter – the smaller F number (reverse ratio). The aperture's values increase and decrease by fixed stops, in which the amount of light is multiplied by 2 or by 1/2 accordingly, and each stop increase or decreases the F number is by a multiple of 1.4 F (1.4 being the square root of 2.) The common stops are: F/1 F/1.4 F/2 F/2.8 F/4 F/5.6 F/8 F/11 F/16 F/22 F/32 F/45 F/64. Of course not all lenses can reach any of these aperture openings and most cameras also have intermediate F numbers between each stop. An F number will pass exactly the same amount of light on all lenses – 200mm lens F/4 will have the same exposure parameters as 50mm lens and F/4. A lens with a wide open aperture is also called a fast lens, as it allows more light in. Most lenses lack some sharpness in their most open aperture and the "Optimal aperture", which results in sharpest image, is usually X2 the widest aperture and so in an F/2.8 lens the optimal aperture will be F/5.6; this is just a guideline and each lens has its own "sweet spot".

Aperture and DOF – Depth of Field is the depth of sharpness in the image in front and behind the focused subject; The aperture affects the Depth Of Field (DOF) : the wider the aperture the shallower the DOF, and vice versa. The shape of the aperture affects the "Bokeh" (Japanese for blur) of the lens; the rounder the diaphragm – the nicer and smoother the bokeh will be. A round diaphragm can be reached by using rounded blades. It's recommended to read the article I wrote about DOF.

Focal length – the lens' focal length represents the distance between the front element of lens and the film or sensor. It doesn’t indicate anything about the physical length of the lens. Wide-Angle lenses utilize a small focal length, while Telescopic lenses utilize a large focal length, in order to take shots of distant objects. We divide Focal Lengths into several groups: less than 20mm – ultra-wide lens; 24-35mm – wide angle lens; 50mm normal lens; 75-300mm – telescopic lens; larger than 300mm – super telescopic lens. Fish-eye lenses use very small focal length, typically 10mm. The larger the focal length, the harder it is to manufacture, the lenses become heavier and more expensive and it's more difficult to achieve wide open aperture. For example, a lens of 500mm (focal length)F/4 would require front elements of at least 125mm in diameter. . There are lenses of fixed focal length and changing focal length (zoom). Usually the fixed focal length will produce higher optical quality since they hold less optical elements and are more precise. In DSLR lenses we find a crop factor multiplier, mentioned earlier in the Sensor size section.

Focus – in order to get a focused image, the light must precisely reach the sensor. To accomplish this, several elements must be moved inside the lens mechanism. Automatic focus works with a linear sensor that has several "pixels" that searches for contrast in the selected focus area. Why search for contrast? Because when an image is out of focus you can't find edges and contrast. The electronic engine in the camera or inside the lens mechanism signals the focus elements in the lens to move back and forth until such contrast is found and then we can take the picture. So, in order to easily focus the camera, we should point the selected focus area at a contrasting object. If the sensors are aligned horizontally, I will point them at something with vertical contrast such as a frame on the wall, and not at horizontal shades. In DSLR cameras, the central focus area is crossed by horizontal and vertical sensors, while the side areas are linear vertical or horizontal. That's why the central area is usually much more sensitive and faster. There are three ways to focus: manual – in which we move the focus ring on the lens; AF single – the camera locks focus while we keep the shutter half pressed for us to recompose; AF continuous (or AI servo) – the camera never locks focus, this setup is good for objects in motion. Lenses with fast focus motor (USM, SWM, HSM etc.) will focus faster. Wide aperture lenses will focus faster under dim light conditions.

Filters – almost every lens has an option for filter threading. The filters allow us more creative results and protection of the lens from scratches and dust. It's recommended to read the "filters" guide for more information. Read Filters Article for more information

Stabilization – especially effective for shaky hands, dim light and large focal length. The stabilizer mechanism usually allows up to 3 stops slower shutter speeds. Nikon calls it VR (Vibration reduction), Canon calls it IS (Image Stabilizer), Sigma went for OS (Optical Stabilizer) and Konika-Minolta's AS (Anti-Shake). The first three use the same principal of a floating element with gyroscopes and a fast motor to reduce to movement. Konika-Minolta's mechanism is based on a sensor on a moving platform instead of a moving lens element.

Perspective – lenses of different focal lengths have different perspectives. A wide angle lens will have a deeper perspective and objects will appear further away from each other; lenses with larger focal length will result in shallower perspective and objects will appear closer to each other. So if we want our swimming pool to look larger, we will use a small focal length.

DOF – Depth Of Field – I explained shortly before, but read the article I wrote about it where everything is explained. DOF Preview, a feature of advanced DSLRs, is a small button near the lens which, when pushed, shows how the DOF will appear in a smaller aperture. In today’s digital cameras, we don't really need it as we can take a picture and see the result directly on the screen.

Distortions – when it comes to lenses and optics, there are many kinds of distortion. There is Barrel Distortion which is created in wide angle lenses and ’rounds' the frame like a barrel, and Pincusion which is the opposite to the Barrel and 'draws' the corners of the frame inwards. Chromatic Aberration is caused when different light wave-lengths are focused on different planes than the camera’s sensor, resulting in red-ish or blue-ish glow around contrasting edges. Vignetting is darkening of the corners, usually occurring in cheap lenses and wide open apertures. Flare is caused usually by direct sunlight and due to reflecting of light between lens elements, due to poor coating.

The Digital Image

After capturing the image using the camera's body, the digital sensor and the lens system, now we have a Digital Image. Let's see what that means in this final episode of photography 101.

Pixel – stands for "Picture Element" and that's the most basic unit of an image. Each photoelectric cell on the sensor creates one Pixel in the image. A Pixel has only one color and no details, it's a simple square.

Resolution – an indication to the amount of detail in the image. The more pixels you have in an image the sharper it will appear and we can make larger prints without losing quality. The resolution is calculated by multiplying the amount of horizontal pixels with the vertical pixels and since the results are in millions we use the word "Mega" which stands for million (in Greek), and that’s where the term "Mega Pixels" got coined. An image that is 3,000 pixels wide and 2,000 pixel high is actually a 2,000×3,000 = 6 Mega Pixel image. A 2 megapixel camera can print a satisfying 10×15 cm image at 300dpi, for a 20×30 300dpi image we will need an 8 Megapixel camera.

Interpolation – some cameras, usually the cheap ones, use interpolation to extend the pixels count. For example a 12 megapixel interpolated camera with 4 million real pixels is a lie, since the camera has only 4 million pixels on the sensor, which are taken and then multiplied in order to produce the said 12 megapixels image. There are several methods for interpolation and here are the most common three.

Digital Zoom – based on the same principal of interpolation as mentioned. It essentially involves cropping and interpolation back to the original resolution. You should avoid the digital zoom and apply crop and interpolation (if needed) with a good image editing software.

Calculating Image Size – Let's see what's the real size of a digital image: If I photograph an image that is 3008×2000 pixels as in the Nikon D70, I produce an image of 6,016,000 pixels (we talked about it before), if I shoot at 24 bit per pixel (we also mentioned that) then the final file would contain 144,384,000 bits. In order to change it to Bytes we need to divide by 8 (8 bits=1 Byte) and so 18,048,000 Bytes, or in short 18.048 Megabyte.

JPEG – Since it's not reasonable to save files in the size we calculated just now, the JPEG algorithm was developed. JPEG stands for "Joint Picture Expert Group" and here’s their homepage. This algorithm manages to decrease the file size substantially by erasing unnecessary information from the image, usually small hue changes that the human eye doesn't even notice. This method decreases the file in a 1:6, 1:10 or any other ratio, so you get a 3 Megabyte file instead of the original 18 MB file. This method is irreversible and the information erased is gone forever. JPEG is now the main format in digital cameras.

RAW – This means the image’s raw data, as retrieved from the sensor, is saved in its original high quality and with no compression. The information contains greater dynamic range, 12-bit per channel (instead of 8), and before any type of manipulation. All the definitions of white balance, sharpness, brightness, saturation etc. are done on the computer. Raw files take much more room than JPEG and need more work on the computer.

White Balance – every light source has different color temperature, which is measured in Kelvin degrees. Low Kelvin (1,500-3,000) indicates red light source (Candle, Tungsten); medium Kelvin is for sun light (around 5,500) and high Kelvin is for shades and cloudy weather (8,000K). if you look at the flames in your home stove you can see that in low temperature the flame is red and in higher temperatures it is blue. The human eye adapts very well to different light sources, but the camera lacks this amazing ability and needs various calculations to achieve the correct white balance in every frame. In auto white balance mode, the camera searches for something white in the frame and can use that as reference for all the other colors. But when the image doesn't have anything white, or it has several light sources, it can mess up, and we can help by adjusting the White Ballance (also written WB) manually or by selecting from a variety of presets.

Sharpening – every image goes through some kind of sharpening. That's done by increasing the contrast in edges of forms. In photoshop you can use the Unsharp-Mask filter, which is a tool that lets you apply contrast in a very efficient way. It's important not to over-do the sharpening, because that could create visual artifacts you’d want to avoid.

Dynamic Range – that's the amount of details we will see in the highlights as well as shadows in the same image. The human eye has an incredible dynamic range, you can sit in a room and look outside a window and see the interior and exterior properly. The camera is much more limited, and we will either see the interior as silhouettes or the exterior washed out with no details. You can increase your camera's dynamic range by using RAW or by taking several images differently exposed and combining them into an HDR (Hyper Dynamic Range).

Summary

After concluding the four parts of photography 101 we know that the camera and the digital systems are very complicated. Here I described the main basic terms, Knowing and mastering the theory can help you gain more from your camera and achieve better results. There is always more to learn and I hope you've made the first step successfully

I Hope you enjoyed part IV of Photography 101 and that you gained new information from the series.

Yours truly,

Roie Galitz