Selasa, 28 Juli 2009

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Basic SLR Cameras

Photography is a very simple process: rays of light reflected from a subject pass through a hole in a box (a camera) to form an image on light-sensitive material (film). But, because light never stays the same and the film may not have the same right amount of sensitivity, the camera needs special controls so that it can be adjusted to allow in the correct amount of light.

These controls don’t make the camera more difficult to use, just more flexible. This flexibilty means that the photographer can shoot many different subjects in different lighting conditions with just one camera. A camera such as 35mm manual focus or auto focus SLR with a range of controls, will enable a photographer to take anything from a happy snaps to breathtaking landscapes, nature subjects, special-effects pictures and, who knows, along the way perhaps some stunning and even inspiring images.

Even high-end 35mm automatic snap-shot cameras, while not versatiles as an SLR, enable you to do much more than just point the camera and press the button.
Both of these camera types are widely available today and both have their pros and cons. A closer look at their features, plus a grounding in camera basics, will help you to make better use of them and improve your photography as a whole.


The Camera

There are two features which controls the amount of light that is transferred on to the film. The first is the aperture, which is a hole with a variable size. Most SLR camera lenses have eight or nine variations of aperture size, known as f-stops. They are shown like this: f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22 and f/32. The widest aperture opening in this range is f/2, while the smalest is f/32.

Aperture control the amount of light entering the camera and getting on to the film. They are adjusted manually via an aperture ring, or electronically on an automatic camera.
The lenght of time that the light is allowed into the camera is controlled by the shutter. Because today’s film are so sensitives to light, shutter speeds are mostly in fractions of a second, with only a few shutter speeds lasting for one second or longer. A typical shutter speed range on an SLR is shown as fractions of a second and full seconds like this: 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, ¼, ½, 1, 2, 4, 8 and B. The letter B refers to “bulb” or “brief” time. At this setting, commonly known as the “B setting.” The shutter stays open for as long as the camera’s shutter button is pressed in. When you lift your finger off the shutter button, the shutter closes.
So, in order to get a correctly exposed image, the aperture and the shutter speed work together to allow a fixed amount of light for a fixed amount of time into the camera and then on to the film, to produce the image. The whole procedureis called the exposure. A correct exposure setting is when the aperture and the shutter speed chosen produce an image that is not too dark and not too light.

Different combinations of aperture and shutter speed will give the same exposure. For example, a setting of f/8 at 1/60 second will give the same exposure as f/5.6 at 1/125 second. Also, the shutter speed in use will depend on whether the photographer wants to freeze the actions, or wants a moving subjects to record as ablur, or simply wants an in-between shutter speed for a subject that’s not moving.

Fast shutter speeds like 1/125, 1/250, 1/500, 1/1000sec or higher will sharply record moving subjects. Slow shutter speeds of 1/60, 1/30, 1/15, 1/8sec or below won’t be able to record moving subjects sharply.


Exposure Modes
All exposure modes come from two basic types: manual exposure, aperture priority auto exposure and shutter-priority auto exposure.

Manual exposure enables the photographer to choose the aperture and the shutter speed that will give the correct exposure.

Aperture-priority auto exposure is a system in which the photographer chooses an aperture and the camera automatically selects the corrects shutter speed.

shutter-priority auto exposure enables the photographer to chooses a shutter speed and the camera automatically selects the correct aperture.

These exposure modes are found in most 35mm SLRs. Some basic SLRs only have the manual exposure mode, while higher level SLRs have these three modes plus many more.
One of these advanced exposure modes is called program. This is fully automatic exposure mode that chooses and sets the correct aperture and shutter speed. Program’s fully-automatic approach is ideal for compact cameras, almost all of which have this mode. It is also included on SLRs as a snapshot mode, used for general picture-taking.

There are versions of program mode that favor shutter speeds or apertures (as with aperture-priority auto exposure). A further refinement of program mode is something called program shift. This feature enables the user to freely adjust the aperture or shutter speed as needed. The camera’s exposure system will then automatically choose the corresponding shutter speed or aperture that will give a correct exposure. Think of it as a combination of aperture-priority auto and shutter priority auto exposure.

For the SLR user, the automatic exposure modes save time in setting apertures or shutter speeds, or both together. Many SLRs on this types also have an auto exposure (AE) lock feature which enables you to lock the exposure for one part of scene or subject. This is useful if there’s a risk of the camera’s exposure system being “confused” by tricky lighting (it does happen!). In this case use the AE lock to take an auto exposure reading of your main subject. Lock it, then compose your shot and take the picture.


The Metering System
The metering system in a 35mm SLR camera measures the amount of light in the scene and calculates the best-fit exposure value based on the metering mode explained below. Automatic exposure is a standard feature in all SLRs cameras. All you have to do is select the metering mode, point the camera and press the shutter release. Most of the time, this will result in a correct exposure.
The metering method defines which information of the scene is used to calculate the exposure value and how it is determined. Metering modes depend on the camera and the brand, but are mostly variations of the following three types:

Matrix or Evaluative Metering

This is probably the most complex metering mode, offering the best exposure in most circumstances. Essentially, the scene is split up into a matrix of metering zones which are evaluated individually. The overall exposure is based on an algorithm specific to that camera, the details of which are closely guarded by the manufacturer. Often they are based on comparing the measurements to the exposure of typical scenes.

Center-weighted Average Metering

Probably the most common metering method implemented in nearly every SLRs camera and the default for those SLR cameras which don't offer metering mode selection. This method averages the exposure of the entire frame but gives extra weight to the center and is ideal for portraits.

Spot (Partial) Metering

Spot metering allows you to meter the subject in the center of the frame (or on some cameras at the selected AF point). Only a small area of the whole frame is metered and the exposure of the rest of the frame is ignored. This type of metering is useful for brightly backlit, macro, and moon shots.


The SLR Viewfinder

The viewfinder is the single most important user interface on any camera. Throughout the history of cameras, the method of aiming the camera accurately and communicating its view to the operator is what has determined and defined most different basic camera types.
Yet the viewfinder is perhaps the single most fudged and botched aspect of today's 35mm SLRs. With the exception of the Contax Aria of the late '90s and the more recent Minolta Maxxum 7, virtually all entry-level to mid-range cameras skimp on the viewfinder. The worst offenders are cameras that are meant to be cheap (they have mirror-box prisms) or cameras that are meant to be small (which usually have poorer coverage).

For the Sake of Clarity
To be clear, let's define a few terms about viewfinders, just in case you're not entirely up to speed. (And if you aren't, don't feel bad. Most people aren't. Why do you think the manufacturers are able to get away with such blatant skimping? An educated consumer is a dangerous consumer. Oh, did I say "dangerous"? I meant "demanding." Or maybe "discriminating." Undesirable, in any event.)










Magnification:
this refers to how big the viewfinder image appears to be in an absolute sense. Like a batting average, it's usually expressed as some decimal fraction of one. 1X is the size that things appear to be when you look at them with your eye (a.k.a. "the naked eye"). Now, obviously, magnification also changes when you use different lens focal lengths — telephotos make things look bigger, wide-angles make things look smaller. So camera magnification is specified with a 50mm lens. Less often stated is that the lens must be set at infinity, because magnification also changes slightly depending on how close or far you focus the lens.

Let's say a camera's magnification is .75X. What this means is that your camera, with a 50mm lens on it, set at infinity, makes things appear to be three-quarters the size they look to be with your naked eye. .5X means half as big; .9X means nine-tenths as big. Better cameras have higher magnification. .88X is better than .67X. You're getting this.
I hope it stands to reason that magnification also determines the apparent relative size of the viewfinder image rectangle. I once tried an interesting little experiment — with identical 50mm lenses on both, I held a Pentax ME Super (high magnification) to one eye and a Pentax ZX-5n (low magnification) to the other. The ZX-5n's viewfinder image fit inside the ME Super's with lots of room to spare.

Coverage: this compares what you can see in the viewfinder with what will be recorded on the film. It's reported as a percentage. If you can see through the viewfinder half of what will be on the negative, that would be 50% coverage.

To further confound matters, coverage is sometimes reported as a linear measure and sometimes as an area measure. To simplify this, imagine a big square drawn on graph paper that has ten little squares per side. The linear measure is 10 x 10 little squares, and the area measure is 100 little squares. Now imagine that we're going to draw a slightly smaller square inside the big one that's smaller by one little square on each side. That square has eight little squares on each side. The linear coverage of the inside square is 80% of the larger one (8 instead of 10); the area coverage is 64% (8 x 8 instead of 10 x 10). You can see from this that when one camera manufacturer reports that its viewfinder has 92% coverage and another reports 95% coverage, you still can't quite be sure how they compare, because one might be reporting linear coverage and the other area coverage.

Now, if you were no expert and just taking a stab at this, you'd probably guess that you would want to see in the viewfinder all of the picture you're about to take. It stands to reason you don't want to see half of it, or a tenth of it, so why wouldn't you just want to see all of it? As with many things, however, it turns out that the uncomplicated answer is not the correct one.


The Lens

The third most important aspect of an SLR camera, apart from enabling the photographer to see through the lens to accurately compose his pictures and to asses focus, is lens interchangeability. Wheter the SLR is a manual focus or an autofocus model, most have access to a huge range of interchangeable lenses that can be used with them.

Manual focus lenses can only be used with manual focus SLRs, while autofocus lenses can only be used with AF SLRs. However, there are exceptions to this rule, namely Nikon. They allow a certain amount of lens interchangeability between their manual and autofocus SLR models. Some independent lens manufacturers (those that don’t have SLR ranges of their own) also produce lenses which allow this type of flexibility.

Manual lenses have a manual focus ring and an aperture ring which has a full range of the most commonly used apertures. A manual focus zoom lens also has a zoom ring, which the photographer can use to alter the focal length. This varies the amount of the scene that will be seen in the viewfinder and the amount of the scene that will therefore be included on film. Typical zoom lens focal lengths are 24-70mm and 70-200mm though there are others with different focal lengths.

























Fast and slow lenses

Some lenses have wide maximum apertures, such as f/1.8 and f/1.4 (the widest aperture commonly found on lenses). There are rarer, very expensive lenses of f/1.2 or even f/1.
Others start with smaller maximum apertures such as f/3.5 and even f/5.6. Wide maximum aperture lenses are preferred to as “fast” lenses, while those with smaller maximum apertures are called “slow” lenses.
Zoom lenses have slower maximum apertures than fixed focal length lenses (ie 28mm, 50mm, 200mm and so on). And a zoom lens’s maximum aperture changes, becoming smaller as it goes toward the long end of its focal length range. So while a 70-200mm f/3.5-5.6 zoom may have a maximum aperture of f/3.5 at the 70mm setting, this will become f/5.6 at the 200mm setting. With fixed focal length lenses, and some zooms, there is just one maximum aperture.

Focusing
Manual focus SLRs need to have the lens focused manually in order to give a sharp image. Autofocus (AF) SLRs are able to automatically focus the lens when the shutter button is pressed. Both have their benefits and though AF SLRs are generally more sophisticated and easy to use, manual focus SLRs mostly cheaper and give a bit more user-control. Some manual focus SLRs are expensive too, and, while lacking autofocus, have other sophisticated features. Because of this and because of the amount of user-control they offer, many of these are popular with proffesional photographers. But many pros in certain fields (for example, sports and news photography) use AF SLRs for their sheer convenience.


Depth of Field

A correctly focused lens will produce a sharp image of the subject you’re photographing. But some subjects such as landscapes, also need to be sharp in the foreground and in the background, as well as the main subjects area. The area of sharpness that extends from in front of, as well as behind, the subject is known as the depth of field.
Wide apertures , such as f/2, f/2.8, f/4 and f/5.6, give shallow depth of field, that is, there is only a narrow area across the subject area which is sharp.
Small apertures – f/8, f/11, f/16, f/22 and f/32 – give greater depth of field, which means that a larger portions of the scene in front of and behind the subject is sharp, as well as the subject itself.

Greater depth of field is ideal for landscapes or just general subjects where you want everything to be sharp focus.














shallow depth of field has its uses, too. A wide aperture can make background details unclear, so the viewer will only concentrate on the part of the scene that is sharp – the main subjects. This can be very effective if photographing a person against a busy – looking background. Use a wide aperture and the distracting background will become indistinct. Shutter-priority exposure modes can do this for you.



















A second benefit of shallow depth of field is that the wider the aperture the faster will be the corresponding shutter speed. This is excellent for photos of people, as a movement, even changing facial expressions, can then be more accurately captured by the camera.


Flash

Flash units are either built-in to the camera or separate. Nearly all the compact cameras and some autofocus SLRs have a built-in flash unit. On SLRs this unit is situated on top of the camera. These units deliver enough power to be useful as emergency flash illumination for subjects within a close range. Some are even more sophisticated and can alter the coverage of the flash illumination to correspond to a (limited) range of lens focal lengths. But none have the power or advanced features of a separate flashgun. This separate unit fits into the hotshoe found on the top of all SLRs. While many of these flashguns are reasonably priced, the more powerful ones can cost as much as a mid-priced SLR.

This is because they are capable of giving illumination over a larger area. And they have additional features that make further use of this power. But there are many low to mid-priced models which give a good combination of reasonable power output plus other features.




















Flash sync
The correct flash synchronization or sync speed is indicated by an “X” near the appropriate shutter speed on the shutter speed dial of a manual focus SLR. Alternatively, the sync speed may be highlighted by being in a different color to the other shutter speeds.
An autofocus SLR’s flash sync speed is shown in the instruction book. Typical sync speed on older SLRs are 1/60sec or 1/90sec. On newer models the sync speeds are usually 1/125 or 1/250sec.

Although shutter speeds faster than the recommended flash sync speed will cause blacking out of part of the image, shutter speed slower than the sync speed will not have this effect.
With very slow shutter speeds, a subject that’s moving will appear as a blur, while flash will sharply freeze part of it. This gives an effect of the movement though if you want to avoid this then stick to your SLR’s fastest flash sync speed for sharp focus shots.

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