Camera Lens

A light-tight box with film in it doesn’t require a lens to expose film—even a pinhole camera can capture an image. But a lens can gather more light than a pinhole. A lens can focus and clarify. It’s the tool we use to define our image.

Scientists and photographers have studied the lens since the early Twentieth Century. Few will describe any lens as technically perfect, although a lens’ unique optical characteristics make it the best choice for a particular shoot.

Lens function is complex. We know that since all visible objects reflect light rays in all directions, we must gather as many rays as possible and get them to our film without distortion. Simple lenses use a single convex glass element positioned so that the light rays from the subject are bent towards and converge at the film. By carefully placing the lens relative to the film, we successfully record an image.

An iris is an aperture of variable size used to control the intensity of light falling on film. The iris control is usually calibrated in f-stops or T-stops. A change of one f-stop or T-stop is equivalent to doubling or halving the intensity of light falling on the film. T-stops are more accurate because they factor for light loss through the lens glasses.

Simple lenses have a limited ability to focus light. Optical distortions can result when light rays enter from the lens perimeter; those rays have to travel farther to reach the film and will be less focused. Toa limited degree we can solve this problem by narrowing the glass width; the resulting loss in light, however,makes the lens “slower.” For each additional stop of light passage in a given lens, the design becomes more complex—the geometric correction becomes more extreme.

Standard, wide-angle, telephoto, and zoom lenses include the ability to adjust focus and iris. Some lenses include a second element, positioned between the first element and the film. Its concave surface compensates for the distortion of the first element. Each element introduces distortion, typically resulting in internal reflection, or flare. The distance between these elements and the precise grind of the glass is critical, and these factors add significant cost to the lens.

An aperture controls the quantity of light passing through a lens. The best lenses perform well at every aperture setting. As such, the precision of the lens must be consistent at every point within each glass element.

Dr. Max Berek of Leitz established image quality standards before 1914 by capturing “miniature” still photographs on 35 mm film. His “circle of confusion” defined the measure of permissible out–of–focus quality in a ten-inch paper photograph. Though modified, this concept endures.

Color is probably the most complex factor in lens design. Because each color has a specific wavelength measured in nanometers, a particular shade has a unique wavelength. Blue objects and red objects will focus in diJerent places on a film frame, whether the film is black-and-white or color. Getting all colors to converge on a single plane despite their diJerent lengths is fundamental to lens design. In 1938 Kodak pioneered the concept of making glass lenses with exotic types of rare-earth elements and cementing them together in each element to correct the aberration.

Zoom lenses were developed later. A good zoom lens must address each of the potential pitfalls while oJering the utility of variable focal length. In motion picture applications, the light transmission, sharpness and individual color focus must remain unchanged despite the focal length change within a shot.

Focal Length and Focus

Lenses are identified by their focal length in millimeters and maximum aperture in f-stops (e.g., 50 mm/f1.4 lens). The focal length is defined as the distance from the optical center of the lens to the film plane. The f-stop is calculated from the dimensions of the lens.

Focal Length and Angle of View

The focal length of a lens determines the angle of view, or perspective, seen through the lens. Normal lenses provide a perspective that approximates human vision.

Lenses that are shorter than normal provide a wider angle of view—they are wide-angle lenses. Lenses that are longer than normal provide a narrower point of view and magnify the subject—they are telephoto lenses. Wide-angle lenses make background objects appear further away; telephoto lenses compress distance and make the background appear closer. Thus, moving the camera toward a subject (as in a dolly move) results in a look that is very diJerent from a scene captured by zooming the lens from a stationary camera position. The apparent separation from the background, making objects relatively smaller, makes camera movement less noticeable. Thus, using wider lenses for hand-held scenes is preferable.

Digital Camera - TRIPOD

Created by James Ryan Carssow © 2009

A tripod is an essential tool of any good photographer. If you have a new camera, especially a DSLR, and are wondering what accessory to buy next, a quality tripod should top your list (followed soon after by a camera-brand external flash).

Why do I need a tripod?

To take photos of landscapes, sunsets, etc. at the peak times of beautiful natural light when you will need to utilize shutter speeds that are too slow for hand-holding your camera. This is the number one most important reason to own a tripod. You will MISS the shot of a lifetime as the sun sets and the sky explodes with orange color if you don’t have a tripod.
Tell me the five best landscape or sunset photos you’ve ever seen and I’ll bet you the cost of your camera that every single one of them was taken with the camera mounted on a tripod.

To take “macro” photos of tiny objects up close. Because of the extremely small apertures (f16, f22, f32) needed to get adequate depth of field in macro photography, the appropriate shutter speed may be too slow to hand-hold your camera.

To take photos of large groups of people. In these situations it is often best for the photographer to compose the shot and focus the camera, then take his eyes out of the viewfinder to scan the group and wait for the moment that everyone is smiling and looking at the camera to finally fire the shutter (a wired or wireless remote shutter release is also helpful here).

To take photos with yourself in them. Please don’t rest your $500 DSLR on the hood of your car or some flat surface in order to take a photo of you and your soul mate together in frontrandom of some iconic place on your vacation. This is how nice cameras get broken or stolen.

To take photos that will be digitally “stitched” together to form a panoramic view. Try doing this once without a tripod and once with. You’ll use a tripod every time after you see the difference in the results.

To take time elapse exposures of stars at night.
To take photos of cityscapes at night
To take photos of small objects to sell on eBay
To take photos of rivers and water falls in which the water appears to be “flowing” in the photo (you need shutter speeds of slower than 1/15th of one second to do this)
To take photos of sleeping babies (or husbands) indoors without flash

Basically … to take photos of any stationary subject in dim ambient light.

What kind of tripod to buy

This is a question with an easy or a complicated answer, depending on your point of view. The easy answer is buy a tripod that best fits your camera and how and where you like to photograph. The complicated answer is that there are hundreds of choices and prices ranging from $25 to well over $1,000. So here are some tips:

Always try out a tripod in person with YOUR camera before buying. This doesn’t mean you
can’t order a tripod over the internet or find a great deal on eBay, but try to test the same or a very similar tripod at a local photography store or from a photographer friend who already owns one. You don’t want to buy a tripod unseen only to realize once you receive it that it doesn’t work well with your camera.

Make sure the tripod is sturdy enough to hold your camera (and lens, flash etc.) steady in all
conditions and at all angles. If you have a heavy professional or semi-professional camera and/or lens, then you’ll need more than a $50 plastic tripod from Sunpak, Velbon, or Slik. But if you have a relatively small and light consumer-level DSLR, then one of these inexpensive tripods will work well.

Make sure the tripod is lightweight enough for YOU to carry it with you. The cliché amongst
photographers is that a cheap lightweight tripod that you actually have WITH YOU is 1000
times better than the heavy and expensive tripod that is sitting at home or in the trunk of your car.

Make sure the tripod “head”, the maneuverable contraption upon which the camera sits, is strong enough to support the weight of your camera and largest lens and a flash. Also make sure it can maneuver in every conceivable direction and that it locks down tight once your desired position is achieved. Make sure the methods of locking and unlocking the head’s movement are easy for you to use. Some are much more complicated and cumbersome than others.

Don’t buy a tripod that is intended for video cameras. The manner in which the tripod head rotates and “pans” is built for video cameras and not still cameras and will not be as maneuverable as you need for a still camera.

Make sure the tripod is flexible enough for your needs. For example, if you like to take macro photos of flowers and other things low to the ground, then your tripod needs to be able to flare its legs out so your camera can be positioned low to the ground. Good professional tripods can hold the camera anywhere from 6 inches to 6 feet above the ground. Cheap, plastic, consumer tripods can only go “as low” as their legs will collapse to when folded up for travel (usually 18 to 24 inches off the ground minimum).

If you own or use more than one camera, then you’ll definitely want a tripod with quick-release plates that screw into the bottom of each camera and then latch onto the tripod. This way you can quickly change from one camera to the other on the same tripod without having to unscrew the tripod screw each time. This is also safer and better for the camera (even if you only own one) because you’re screwing a small lightweight plate into the bottom of your camera, and not the entire tripod.

If you’re using a very large lens to photograph sporting events (something that costs at least
$1500 new) then you need a monopod, not a tripod. If you’re not using such a lens, then you do not need a monopod to photograph sports. If you mount your camera, and not your lens, to the monopod, then you don’t need a monopod.

Tips for photographing with a tripod

Tripods are really quite self-explanatory. Just adjust the legs to the height you want, then rotate, tilt, and pan the head until your camera is positioned properly. But there are a few tricks to know when using a tripod:

If you need a tripod for your photograph, it’s likely because of slower shutter speeds that would cause “camera shake” and blur from hand-holding the camera. If this is the case, then often even the motion of pressing the shutter button can blur the photo slightly even if mounted on a tripod.

There are two solutions to this:
Use a remote shutter release
Use the self-timer built into your camera. Any shaking motion caused by your finger depressing the shutter button will fade after a few seconds. So set your self-timer to 10 seconds, press the shutter, and the photo will be taken – shake free – 10 seconds later.
Many DSLRs have “grid lines” inside the viewfinder that can be turned on with a menu function (check your user manual). These lines are great for helping you level the horizon of a landscape photo so that the photo does not appear “tilted” if the horizon is not straight across. Don’t rely solely on any bubble level built into your tripod, as the horizon itself may not be perfectly level.

If the ground you’re working on is uneven, then adjust the legs of your tripod to compensate.
Don’t extend all three legs all the way and then let the tripod lean on the uneven ground. There’s a good reason the three legs adjust height independently, and this is it.

Try using your tripod at different heights to get new perspectives on typical subjects. Don’t be afraid to work with your knees, butt, or even belly on the ground.

For taking tripod-mounted photographs with the camera tilted to vertical orientation, it is best to use specialized camera-rotating brackets (available at good photography stores or online) that keep the camera’s center of gravity directly over the center of the tripod. Using the basic tilt function built into many tripods allows the camera to lean to one side of the tripod and could, in some cases, cause the camera to shake enough to blur a photo or even cause the tripod and camera to fall to the ground.

BE CAREFUL when using a tripod or monopod as they often give a false sense of security that your camera is completely stable and secure. One wrong spin or turn and you can knock over your tripod, sending your expensive camera to an early death on the hard ground below. SCARY

STORY – a former photographer colleague of mine once rested his monopod mounted camera and lens on a stadium wall for a brief second while digging another memory card out of his pocket. The top-heavy combination quickly slid off the wall, crashing to the concrete below. Both his $5,000 Nikon D2X camera and $6,000 Nikkor 200mm f2.0 lens were ruined – even the Nikon factory could not repair either.

Digital camera - ISO

Created by James Ryan Carssow © 2009

ISO, along with White Balance, is what sets digital cameras apart from 35mm film
cameras. With film, you loaded one roll of film and used that film speed for that entire roll. If you wanted to use a different film speed, you waited until you changed rolls. With digital, you can change the ISO setting for each photograph if you desire. This opens up a whole new world of options by allowing the third element of exposure – ISO – to be adjusted for each photo, just like shutter speed and aperture.

The trade-off:
A higher ISO is more sensitive to light (brighter), but usually offers less pleasing overall results because of increases in “grain” or “noise” in the final image and less overall sharpness, crispness, and color saturation.

A lower ISO is less sensitive to light (darker), but usually offers more pleasing overall results because of less grain/noise and better overall sharpness and color.

But this trade-off changes every year as the higher ISO settings in newer cameras get better and better. Five years ago, ISO 800 looked really crummy on even professional DSLR cameras. But today, ISO 800 looks good and even ISO 1600 is adequate for many uses.

General rule of thumb (circa 2008) to ensure pleasing results:

Small point-n-shoot cameras – stay at 400 or less
Consumer DSLRs and other advanced amateur cameras – stay at 800 or less unless you must go higher (i.e. night or indoor sporting events)
Professional DSLRs – 1600 or higher depending on camera model

Note: Some cameras allow auto ISO or “high auto ISO” … be careful of this because the camera may not choose the best ISO for your particular situation. Often, unless you need a fast shutter speed or a deep depth of field, it is better to shoot at 125 f5.6 400 than 250 f8 1600 because the “grain” or “noise” at ISO 1600 will degrade the photo.

Some basic photography truths …

Created by James Ryan Carssow © 2009

Photographing outdoors vs indoors Photographing outdoors in good daylight is EASY for any camera. I’ve seen good outdoor photos taken with a shoebox pinhole “camera” – seriously.
Photographing indoors or at night in sub par light is CHALLENGING for any camera and any photographer.

Shooting moving subjects

Shooting moving subjects (i.e. sports, pets, children) indoors or at night without adequate auxiliary lighting sources is EXTREMELY DIFFICULT for any camera and any photographer, and beyond the capabilities of many “consumer level” DSLR cameras and lenses. Yes, even if you paid $500 or $1000 for your camera you may be unable to get Sports Illustrated quality photos of your child’s 7 pm football game.

Lenses 
If you’re going to spend the money on a top-flight name-brand camera (Nikon, Canon, Olympus etc.) then buy the same name-brand lenses, flashes etc. in order to get the best performance from an entire camera system. There is no point to spending good money on a Nikon camera only to stick a mediocre Sigma, Tamron, or Quantaray lens on it. Retailers like Ritz/Wolf camera love to push off-brand lenses because their profit margins are higher on these cheaper products. But the most important part of any camera system is the quality of the glass in the lenses. Don’t skim on the glass to spend more on the electronics. As a general rule, DSLR cameras lose more than half their value in the first year; while quality, name-brand lenses often sell years later on the used market for 80% or more of their original purchase price.

megapixels The number of megapixels a camera utilizes is nearly meaningless as a measurement of the effectiveness of the camera or the quality of photos produced by it. Any camera with 4 megapixels or better is more than enough for any photograph printed 12x18 inches or smaller, and many 4 megapixel images can be printed as large as 2 foot x 3 foot if properly exposed and in sharp focus.
Megapixels are a misleading gimmick relied on by camera salesman to convince uneducated buyers to spend more money. Ever heard a camera salesman say, “this camera is twice as good, it has 8 megapixels and the other only has 4”. Well, just because the number 8 is double the number 4 does not mean an 8 megapixel image is twice as large (or twice as good) as a 4 megapixel image. A 4 megapixel image is approximately 2450 pixels by 1650 pixels = 4 million pixels. An 8 megapixel image is approximately 3600 pixels by 2400 pixel = 8 million pixels.
Look at the numbers: 3600 is not twice as much as 2450. And 2400 is not twice as much as 1650.

At best an 8 megapixel image is 50 percent “larger” than a 4 megapixel image, and in reality it is less significant than that in terms of a difference noticeable to the human eye. In order to achieve an image size twice as large as 4 megapixels, you need an image that is 4800 pixels x 3600 pixels or approximately 16 megapixels. And for what photographic purpose would you need 16 megapixels? To print billboards? Unless
you’re a professional making money on photography that requires extremely large prints, any camera offered for sale as of 2008 already has more megapixels than you’ll ever need or use.
So if given the choice between buying two very similar cameras, especially if from the same manufacturer, go for the camera with fewer megapixels because it will cost significantly less and offer no significant reduction in photographic quality. Camera makers and sellers love to charge hundreds of dollars more for a few more megapixels. Do the math and you’ll see the difference is negligible. Look at photographs taken with each camera and you’ll see the difference is even less.

One of the biggest scams in camera sales as of Christmas 2008 is the Nikon D60 a 10 megapixel DSLR camera that sells for $700 with a lens when compared to the Nikon D40, a nearly identical camera with 6 megapixels that sells for $450 with a lens. That’s a difference of $250 for 4 extra useless megapixels.

Of course, many cameras with higher megapixel counts also offer many other legitimate improvements over lower-megapixel cameras. The Nikon D200, for instance, was a quantum leap improvement over the D100 model it replaced, not because it had 10 MP to the D100’s 6 MP, but because it was built of stronger titanium alloy, had a more sophisticated autofocus system, a faster frame-advance rate, a significantly better flash system, a larger and brighter LCD screen, better ergonomics and menu design, and many other advances making it a better overall camera/

DSLR camera

Why buy/use a digital SLR camera?

 - flexibility
 - speed
 - manual control
 - to take your photographic possibilities beyond the limitations of “point and shoot”
 - better inherent image quality because of larger imaging sensors and more sophisticated exposure meters and autofocus systems


What is a DSLR camera and how is it different from other types of digital cameras?

DSLR = digital single lens reflex. An internal mirror reflects the view directly from the  photographic lens into the viewfinder. When the button is pressed to take a photo, this mirror is instantly pulled upward (this is the “clicking” or “tapping” noise you hear) and out of the way of the shutter, which slides open to expose the imaging sensor (the digital “film”). Because you see directly through the photographic lens, there is no need for a second “viewing” lens (as with older camera designs), thus – single lens reflex.

The SLR design is superior to other designs because it allows the photographer to see through the viewfinder exactly what is seen through the lens and what will be “seen” by the imaging sensor. When looking through the viewfinder of non-SLR cameras, the image seen is not exactly the same that the imaging sensor or film “sees”.

Point-n-shoot digital cameras have electronic LCD viewing screens at the rear of the camera that show a digital representation of the view through the lens. But an SLR is still the only camera style that allows a real-time optical view through the photographic lens. This inherently allows for faster and more precise operation of an SLR camera over other types.

SLR System

SLR System - How does it look

Cross-section view of SLR system:
1: Front-mount lens (four-element Tessar design)
2: Reflex mirror at 45-degree angle
3: Focal plane shutter
4: Film or sensor
5: Focusing screen
6: Condenser lens
7: Optical glass pentaprism (or pentamirror)
8: Eyepiece (can have diopter correction ability)

Camera Flash

Created by James Ryan Carssow © 2009

Use of flash with older film cameras was often a misunderstood and feared facet of photography for many novice photographers. But today’s digital TTL (through the lens) automated flash systems are technological marvels that take most of the guess-work out of using photographic flash.
An in-depth examination of flash would take up too much room for this guide, but suffice to say using the TTL flash mode on your camera or external flash is all you need to use most of the time, with perhaps a few tweaks for various situations.

 Camera-brand flash

When buying an external hot-shoe mounted flash, you should always use the camera-brand flash. The flash systems of top DSLR camera manufacturers like Nikon and Canon are extremely sophisticated and engineered to work seamlessly with their own brand of cameras and lenses.
Buying the camera-brand flash is a no-brainer. Don’t waste your money on an off-brand flash like Sunpak, Quantary, or Vivitar.
In the film days, those companies made cheaper flashes that produced decent results. But with digital – which is much more technologically difficult to sync with flash – using anything other than the camera brand flash system is just asking for headaches and poor results.
If you ever get to the point of buying the larger studio strobe systems, then you can buy something other than the camera brand. But you’ll need to know how to set up and control those studio flash systems manually.

Types of flash

Built-in on-camera flash or “pop up flash”

• Convenient (don’t have to worry about carrying extra gear)
• Decent results when used properly for subjects at short distances.
• Only option is straight ahead “deer in headlights” flash
• Limited power and flexibility

External hot-shoe mountable flash

• Flexible – point the flash head in any direction 360 degrees to bounce the light off of walls, ceilings etc. for a softer flash effect
• When coupled with a diffuser box (translucent white plastic cover over the flash head) and bounced off a low- to moderate-height ceiling at a 45-degree angle delivers the most pleasing and evenly distributed on-camera man-made light possible.
• Much better power and distance/range than built-in flash, but not up to capabilities of professional strobes
• One extra piece of equipment to lug around

Professional strobes and studio lighting systems

• Best man-made lighting option available
• Extremely expensive
• Complicated (too complicated for further discussion in this guide)
• Not easily portable – these large and cumbersome lighting systems often require two or three large cases full of equipment to operate

When and how to use flash

When, where, and how to use flash still confuses many novice photographers. The common
misunderstanding is that flash is only needed indoors or to freeze action. Most novice photographers would never consider using flash outdoors under bright sunlight, which is actually one scenario where “fill flash” is most needed.

Here are some tips …

Indoors – this is when most “automated” cameras use flash. When there is not sufficient natural light to get a decent exposure at hand-held shutter speeds, flash is used to augment the natural light with often mediocre results. Here are ways to improve indoor flash exposure:

Don’t use flash at all. Unless you need flash to help freeze people or other movingsubjects, many indoor photos are better without flash. If you can gain proper exposure and a fast enough shutter speed without flash, then do so, or use a tripod or IS/VR capable lens. Placing subjects, especially for portraits, near windows to allow outside light to illuminate the subject is a classic technique.

Bounce or diffuse your flash – this is when an external hot-shoe mounted flash becomes your most important photographic tool. Watch your average wedding photographer working the reception area. He/she will almost certainly have an external flash and will often diffuse the light through a soft box or by bouncing the light off the ceiling. This gives a much softer, more even exposure than the typical “deer in headlights” straight flash effect. It also greatly reduces the chance of “red eye”. Red eye, by the way, is caused by the flash being too close to the camera lens and firing too much light too directly at the eyes. With the external flash mounted higher above the camera lens and the light bounced or diffused, the chances of red eye are greatly diminished.

You can try diffusing the light from your camera’s pop-up flash by putting a piece of wax paper in front of the flash. But beware the pop up flash has little flash power to begin with and diffusing it in this manner will reduce that power even further. So be sure your subjects are physically close and that you don’t want/need to see much detail in the background, which will likely show up as almost black. Balance the flash exposure with the ambient room lighting exposure by reducing the power of the flash (look up flash exposure compensation in your user guide) so that both the foreground subject and the background surroundings are properly exposed and visibly detailed. This can often be semi-automated with a “SLOW” setting on your camera or flash. Some cameras, especially the point-n-shoot variety, also call this the “NIGHT” flash setting or “PARTY MODE”. But be careful when doing this to customize your white balance. Ambient light from incandescent or fluorescent bulbs combined with pure white light from the flash can produce some strangely colored results. If you want to get very particular about this, there are colored “gels” or filters that fit over your flash head (just like colored lens filters) to correct white balance issues when combining flash light with ambient lighting.


Outdoors – this is where most automated cameras don’t use flash, but where it is often most useful.

Under bright sunlight conditions, especially when photographing people for posed shots and portraits, USE YOUR FLASH. The automated system in your camera won’t do it for you. You have to “force” your camera to fire the flash on a manual or semi-manual setting. Using flash in bright sunlight is called “fill flash” and is perhaps the most important and under-utilized use of camera flash. When human subjects are lit by extremely bright mid-day sun, faces often become a mixture of properly exposed bright areas and dark, detail-less shadows. By using proper fill flash, the subject’s entire face is brightly lit with little to no shadow and the result is a bright, beautiful face against a bright and beautiful sunlit background. Fill flash in bright sunlight is the same basic technique used by the photographers who shoot models in bikinis for the Sports Illustrated swimsuit issue and other publications (along with reflectors, shades, and other more complicated techniques). Most TTL flash systems are great at fill flash, with some minor tweaking of flash exposure compensation. But YOU, the photographer, must initiate the use of flash under bright sunlight. The camera’s auto mode simply will not do this. AND this is really one of the ONLY times you should ever use full power straight ahead flash. If possible, you should always bounce or diffuse your flash if not in direct sunlight.

With subjects in shade but a bright sunlit background, you can use flash to “balance” the exposure of the subject and background. If flash is not used, then to properly  expose the shaded subject, the sunlit background will be over-exposed. Or, more commonly, the whole photo will be “properly exposed” according to the camera,  leaving the shaded subject underexposed and dark. Using flash to balance a shaded subject against a bright background may require some tweaking of white balance, but usually not to the extent needed for balanced indoor flash.

Subjects outdoors at night offer the same difficulty with flash exposure as indoor subjects, but without the easy solution of bouncing a flash off a ceiling. Try using your flash pointed straight at the subject but with SLOW or REAR flash setting. Or diffuse  your straight ahead flash and adjust flash exposure compensation until you get a pleasing result. If photographing distant subjects at night, no flash in existence will have enough power to illuminate the scene or subject. You’ll need to use a long  exposure and a camera mounted on a stable tripod.

Lastly, many photographers will attempt to use flash to freeze action when they cannot achieve a fast enough shutter speed to do so. This is OK if there is no alternative, but do not expect stellar results.
You can expect plenty of “deer in headlights” exposures with visible and detailed subjects but backgrounds that quickly fade to black. Also this technique greatly increases the probability of red eye in human subjects. And using this technique is banned at many sporting events as it interferes with the players’ ability to see clearly. Worst of all, using flash in any circumstance takes a lot of battery power. But using flash as the main “spotlight” form of illumination will drain batteries in record time. And portable flash units do not have  sufficient battery power to quickly “recycle” for a subsequent full power burst of light.
So even if your camera can photograph 5 frames per second, only the first one or two of those frames will even be visible as the flash fails to recycle its power and thus fails to fire at all for the last few frames of a quick burst.

Internal Combustion Engine - Spark ignition engine

Internal combustion engines are devices that generate work using the products of combustion as the working fluid rather than as a heat transfer medium. To produce work, the combustion is carried out in a manner that produces high-pressure combustion products  that can be expanded through a turbine or piston. The engineering of these highpressure  systems introduces a number of features that profoundly influence the formation of  pollutants.

There are three major types of internal combustion engines in use today:

 (1) The spark ignition engine, which is used primarily in automobiles;

 (2) The diesel engine, which is used in large vehicles and industrial systems where the improvements in cycle efficiency make it advantageous over the more compact and lighter-weight spark ignition engine;

 (3) The gas turbine, which is used in aircraft due to its high power/weight
ratio and also is used for stationary power generation.


Each of these engines is an important source of atmospheric pollutants. Automobiles are major sources of carbon monoxide, unburned hydrocarbons, and nitrogen oxides.

Probably more than any other combustion system, the design of automobile engines has been guided by the requirements to reduce emissions of these pollutants. While substantial progress has been made in emission reduction, automobiles remain important sources of air pollutants. Diesel engines are notorious for the black smoke they emit.
Gas turbines emit soot as well. These systems also release unburned hydrocarbons, carbon monoxide, and nitrogen oxides in large quantities.
SPARK IGNITION ENGINES

The operating cycle of a conventional spark ignition engine is illustrated in Figure 1.
The basic principle of operation is that a piston moves up and down in a cylinder,
transmitting its motion through a connecting rod to the crankshaft which drives the vehicle.
The most common engine cycle involves four strokes:

1. Intake. The descending piston draws a mixture of fuel and air through the open
intake valve.

Figure 1 Four-stroke spark ignition engine: stroke 1. intake; stroke 2. compression; stroke 3. power; stroke 4, exhaust.

2. Compression. The intake valve is closed and the rising piston compresses the fuelair
mixture. Near the top of the stroke, the spark plug is fired, igniting the mixture.
3. Expansion. The burning mixture expands, driving the piston down and delivering
power.
4. Exhaust. The exhaust valve opens and the piston rises, expelling the burned gas
from the cylinder.

The fuel and air mixture is commonly premixed in a carburetor. Figure 2 shows how engine power and fuel consumption depend on equivalence ratio over the range commonly used in internal combustion engines. Ratios below 0.7 and above 1.4 generally are not combustible on the time scales available in reciprocating engines. The maximum power is obtained at a higher ratio than is minimum fuel consumption. As a vehicle accelerates, high power is  needed and a richer mixture is required than when cruising at constant speed. We shall  return to the question of the equivalence ratio when we consider pollutant formation, since this ratio is one of the key factors governing the type and quantity of pollutants formed in the cylinder.

The ignition system is designed to ignite the air-fuel mixture at the optimum instant.
Prior to the implementation of emission controls, engine power was the primary concern in ignition timing. As engine speed increases, optimal power output is achieved

Figure 2 Variation of actual and indicated specific fuel consumption with equivalence ratio and load. BSFC denotes "brake specific fuel consumption. "

by advancing the time of ignition to a point on the compression stroke before the piston
reaches the top of its motion where the cylinder volume is smallest. This is because the
combustion of the mixture takes a certain amount of time, and optimum power is developed if the completion of the combustion coincides with the piston arriving at socalled top dead center. The spark is automatically advanced as engine speed increascs. Also, a pressure diaphragm senses airflow through the carburetor and advances the spark as airflow  increases.

Factors other than power output must be taken into account, however, in optimizing the engine operation. If the fuel-air mixture is compressed to an excessive pressure, the mixture temperature can become high enough that the preflame reactions can ignite the charge ahead of the propagating flame front. This is followed by very rapid combustion of the remaining charge and a correspondingly fast pressure increase in the cylinder. The resultant pressure wave reverberates in the cylinder, producing the noise referred to as knock (By et al., 1981). One characteristic of the fuel composition is its tendency to autoignite, expressed in terms of an octane rating.

High compression ratios and ignition spark timing that optimize engine power and efficiency lead to high octane requirements. The octane requirement can be reduced by using lower compression ratios and by delaying the spark until after the point for optimum engine performance. Emission controls require additional compromises in engine design and operation, sacrificing some of the potential engine performance to reduce emissions.

Advantage of the CMOS Sensor

Sony - April 2011

1. Introduction

Existing mainstream analog security surveillance cameras have being using analog signals with a video format that can then be sent through a single BNC cable using a TV format (NTSC, PAL). Today’s typical imager is the CCD sensor in analog security surveillance cameras. Until a few years ago, the other type of imager, the CMOS sensor (mainly VGA) had been used in web cameras and some imaging devices. 

 

2. Comparing CCD & CMOS

Although both image sensors act as capture devices for a camera, the latest CCD and CMOS sensors are very different in structure. Figure 1 describes these structures. 

CMOS sensors structure

CCD sensors structure

CMOS sensor - Advantage power consumption and speed

To use CCDs in video applications, it is necessary for all the vertical and horizontal shift registers to constantly relay received image data as electronic signals. As a result, there is a limit to achieving high resolutions and increasing speed. Additionally, power consumption becomes comparatively high.

On the other hand, CMOS sensors only need to move one readout column of circuitry, so power consumption is low and it’s easy to increase speed.

3. CMOS Sensor “Exmor”

In recent years, with growing interest in small HD-resolution camcorders, there has been significant development of CMOS sensors which are low power consumption devices with high-speed image readout capabilities. In the field of security surveillance, this development is accompanied by the increasing prevalence of IP networking, which in turn builds demand for HD resolution, as the digital of the network surveillance camera signal does not depend on a conventional TV format.

Because of these growing needs, Sony has amassed its image quality knowledge accumulated in CCDs, and dedicated this to creating new, more advantageous high- speed, high-resolution CMOS sensors. The result is a CMOS sensor with an entirely new structure: the “Exmor”.

Both CCD and CMOS sensors have the same part that converts light into electricity (a key element of image quality). With the “Exmor”, however, Sony uses high image quality pixel technology accumulated in CCD development to enlarge as much as possible the light-receiving section of the photodiode.

Tables 1 and 2 show specifications and Image Sensor Characteristics for the “Exmor” CMOS, CMOS and CCD sensors. 

 

(Table 1) Specifications

Item	IMX035	IMX012	ICX445
Sensor type	“Exmor” CMOS	CMOS	CCD
Image size	Diagonal 6.08 mm (1/3 type)	Diagonal 4.7 mm (1/3.8 type)	Diagonal 6.0 mm (1/3 type)
Transfer method	All-pixel	All-pixel	Interline
Total number of pixels	approx. 1.49M pixels 1384 (H) x 1076 (V)	approx. 1.33M pixels 1304 (H) x 1017 (V)	approx. 1.32M pixels 1348 (H) x 976 (V)
Number of effective pixels	approx. 1.39M pixels 1329 (H) x 1049 (V)	approx. 1.28M pixels 1296 (H) x 985 (V)	approx. 1.25M pixels 1296 (H) x 966 (V)
Chip size	7.64 mm (H) x 7.64 mm (V)	6.452 mm (H) x 6.402 mm (V)	6.26 mm (H) x 5.01 mm (V)
Unit cell size	3.63 μm (H) x 3.63 μm (V)	2.925 μm (H) x 2.925 μm (V)	3.75 μm (H) x 3.75 μm (V)

(Table 2) Image Sensor Characteristics

Item		IMX035	IMX012	ICX445	Remarks
Sensitivity (F5.6)	Typical value	460 mV	290 mV	460 mV	3200K, 706 cd/m2 (Exposure time: 1/30 s)
Saturation signal	Minimum value	830 mV	550 mV	350 mV	Tj = 60 °C

Another major element that determines image quality is noise reduction. In “Exmor” CMOS sensors, noise on the analog part is eliminated by the built-in Correlated Double Sampling (CDS) circuit. Other new structural elements drastically also decrease the noise-contamination level.
Figure 2 and Figure 3 describe these structures.

• The A/D conversion conventionally done just before signal readout is now performed immediately after the light-to-electricity conversion, and is performed for each column. This helps to reduce noise because the analog circuit is made shorter, and the frequency lower.

• Noise-elimination circuits (CDS circuit) are equipped in the digital domain in addition to in the analog domain.

Conventional CMOS sensor structure vs “Exmor” CMOS sensor structure

Through these methods, rapid improvements have been made in CMOS sensor image quality, achieving the same performance level as CCD sensors.

Taking the example of recent, typical Sony IP cameras, the minimum object luminance specifications for cameras equipped with either a CCD or an “Exmor” CMOS sensor are as follows:

Sony CCD network surveillance camera SNC-CM120: 1.3M CCD equipped 0.8 lx Sony CMOS network surveillance camera SNC-CH140: 1.3M CMOS equipped 0.2 lx .

What Are the Different Types of Agricultural Tools?

Many items that are commonly found in garages and backyards are actually agricultural tools. Although rakes, shovels, and other hand tools may not be essential to the average person, they can be very important in an agricultural setting. The fact that some of these items have been used for generations shows the longevity of a good idea.

A spade is a tool that is often used for agriculture. Laymen, however, commonly confuse the spade with the shovel. They are both old tools that are very similar, but they are not exactly the same. Spades tend to have flat edges and lack the curved head that shovels usually have. This makes the spade a good digging implement, but it is not very suitable for carrying materials.

Rakes and hand cultivators are two other agricultural tools that may be confused. A rake can be considered a handheld cultivation tool, and the two implements can be used for many of the same purposes. When a person in the agricultural industry speaks of a hand cultivator, however, he is most likely referring to a shorter tool that has three tines and requires a person to bend or stoop to the ground to use it.

A plow is a tool that is designed to turn over layers of soil. While most people can generally agree on the purpose, they may not all agree on how the tool works since there are different types. For large, commercial agriculturists, a plow is likely to be described as something that is attached and pulled behind a tractor. In rural areas and less developed countries, some farmers still use the more traditional method of hooking their plows to horses or donkeys and having the animals pull them.

Another tool that may look different from one farm to another is a sprayer. These agricultural tools are used for a number of purposes such as distributing fertilizers or pesticides. They come in various shapes and sizes.

Some sprayers have a tank where a substance is stored and long arms that branch out from the tank. These can be hooked to a tractor, and as it moves along, the substance from the tank is sprayed through the arms. Other sprayers have tanks that are carried on a person’s back. The tank is connected to a hose that has a wand, allowing a person more control over what he sprays.

Knives are generally recognized as culinary tools but are not commonly recognized as agricultural tools. They do, however, play an important role in some segments of the industry. Sugarcane is a crop that is still largely harvested by hand. A cane knife, which is often designed like a machete with a hook on the tip, is widely used for this task in many countries. Harvesting knives are also popular in the banana industry.

How to Buy a Digital Camera

Buying a digital camera can be disorienting. There are hundreds of cameras available at many different types of retail outlets (online and in traditional stores), with prices ranging from $75 to several thousand dollars. In this digital camera guide, we aim to help you overcome some of this confusion.

Buying a digital camera can be disorienting. There are hundreds of cameras available at many different types of retail outlets (online and in traditional stores), with prices ranging from $75 to several thousand dollars. Some cameras are small enough to fit in a shirt pocket. Others are large and can weigh up to two pounds. Some are easy to use. Others look like you need an engineering degree to operate them. And almost all are advertised with abbreviations that can be cryptic and confusing for the novice. In this digital camera guide, we aim to help you overcome some of this confusion.

What is a digital camera?
The first step is to understand what a digital camera is. With a film camera, an image is formed by collecting light from a particular scene or subject and focusing on film, which reacts chemically when struck by light and is said to "capture" the image. What makes a camera "digital" is that, instead of film, it has an image sensor that reacts to light by sending out electrical signals.
The camera takes the information from the image sensor and processes and stores it as a collection of pixels in a digital file, usually on a memory card inside the camera. Although the actual process is more complex than that, in essence it is how a digital photo image is made. It's essentially made up of thousands and thousands of tiny dots, or pixels.

What are megapixels?
When you collect a million pixels, you have a megapixel. The number of megapixels tells you how many pixels the image file has. A camera that captures 8 million pixels, for example, is called an 8-megapixel camera. The number of megapixels a camera features can also help to determine the size photos you can print or the amount of cropping you can do. For example, a 4-megapixel camera may be enough for snapshots, but if you want to print poster-size images or crop heavily, 8 megapixels (or greater) is more suitable.
A 6-megapixel camera might be all you'll need because higher resolution doesn't necessarily produce better prints. Lenses and other factors affect quality too. But most cameras today have at least 10-megapixel sensors. The size of the sensor, and the size of each individual image sensor element, which corresponds to pixels, can affect photo quality. But remember, the number of megapixels alone doesn't determine the quality of a digital camera's images.

Types of digital cameras
Our Ratings are divided into two main categories: Basic cameras, are simple point-and-shoots with just the features needed for routine shots, and advanced cameras, which are feature-laden cameras that include sophisticated point-and-shoot and models that let you chance lenses. Note that all point-and-shoots, whether basic or advanced, include cameras with lenses built into the camera (that is, non-removable).
Our basic camera category is divided into three subcategories: subcompacts, compacts and superzooms.
Subcompacts fit in a pocket, are lightweight but generally have few manual controls. A few include nontelescoping zoom lenses, and others have zooms as high as 14x. Compacts are a bit larger, and often have more manual controls than subcompacts. They can also be among the most inexpensive cameras available.
Superzooms offer 15x or greater zoom, with some recent models including optical zooms as great as 30x. Like compacts, superzooms often, though not always, include manual controls. They're also among the more expensive basic cameras.
Our advanced camera category is also divided into three subcategories: advanced point-and-shoots, SLR-like and SLRs.
Advanced point-and-shoots have a nondetachable lens but differ from basic models because they have lots of manual controls, a hot shoe for an external flash, and support for RAW files. It's the lightest advanced type. SLR-like models have interchangeable lenses, but they lack a through-the-lens viewfinder. They're smaller and lighter than an SLR but usually larger than a point-and-shoot. SLRs have the most features, with interchangeable lenses and the largest sensors for the best image quality in low light, and a through-the lens viewfinder. Controls are extensive. They're also the heaviest, most expensive cameras.

Next steps
After you consider the type of camera you want and the number of megapixels you need, but before you dive into specific models, be sure to check out our brand profiles, which outline many of the most popular camera product lines and their respective character traits.
Next, look to our Ratings and Recommendations (available to subscribers) for the models that have the best performance and image quality, including scores for how models capture regular, low-life and flash photos. If you're interested in how well a camera captures video, consider the video quality score. And to see which models respond the quickest, consider the response time score, which is an overall speed judgment, including start-up time and the shutter delay for the first and later shots. In most cases, our Ratings found that point-and-shoot cameras take decent snapshots. So, look through our Ratings for specific features that are important to you. For example, if you want a point-and-shoot that has a better LCD than others, look for a model with a Very Good LCD quality score. Or, if you want a model that includes a touch-screen LCD, look for that in our Ratings. There are also scores for how well a camera handles shake, which can cause blurry photos, its controls, and versatility.

What you'll spend
For many, price is a major factor when buying a camera. In general, look to pay the following for the type of camera you're looking to buy:

• For basic point-and-shoots (subcompacts, compacts, and superzooms), expect to spend $100 to $400.
• For advanced point-and-shoots, expect to spend $350 to $600.
• For SLR-likes, expect to spend $450 to $1,200.
• For SLRs, expect to spend $500 to $2,000.
When you're ready to buy, consider where you will make your purchase. Although some walk-in stores, such as photo-specialty camera shops, might have knowledgeable salespeople, you can't rely entirely on the staff of walk-in stores to assist you in your purchase. Use the internet and our Ratings for information before buying. Also, if you decide to purchase at a traditional retail store, forgo the extended warranty because digital cameras have been among the most reliable products in our surveys.
Many respondents in our surveys found online shopping to be a more satisfying shopping experience than walk-in-store shopping. Most walk-in retailers offer either low prices or wide selection. But some online retailers offer both. But be cautious of very low prices and verify that the camera isn't refurbished or gray market (diverted from other retailers or not meant for sale in the U.S.).