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Comd Dial.jpg
A command dial commonly found in current Canon's AF EOS SLR cameras are a newer way of input and selection of various camera function. Conventional way of setting aperture value on the aperture ring on the lens is not required unless you are in manual override mode. Other manufacturer such as Nikon has also followed this method in their newer series of AF SLR cameras, where your pointer finger is used for controlling input such as aperture value and the thumb is used for shutter speed selection.

What is an Exposure ?

It can be explained as the quantity of light allowed to act on a photographic material; a product of the intensity (controlled by the lens opening) and the duration (controlled by the shutter speed or enlarging time) of light striking the film or paper (darkroom or in the color-lab).

slr1.jpg slr2.jpg slr3.jpg slr4.jpg
Viewing, metering through the Lens (TTL)

Mirror flip-up, Lens diaphragm stopped down, light reaching the film exposure is formed

Shutter curtain closes, reflex mirror stays down, back to TTL viewing

First, you MUST understand a fact, i.e. there is no such thing call a "
perfect exposure". It is all a matter of personal preference - well, only the photographer who did the image capture process will "hold" the rights and judge whether it is or it is not a "good" exposure. Virtually all modern cameras have a reflective photo cells (see SPD or Cds) built in to give you a indication what a recommended proper exposure is - basing on the brightness of the scene with the type and speed of the film in use. The term "proper exposure" is built around a reference where the photo cell read a 18% gray reflectance (most neutral in photography and resemble most outdoor environment) and give you the "suggested" reading (you may override those values).

Over exposure preferred exposure Under exposure

Exposure can a very subjective matter. I would think it is more like a personal interpretation. In this series of three pictures on the magnificent Kuala Lumpur City Centre (KLCC) beside my office (once the tallest human-made structure as at year 2003). I preferred the center image as the start-off photo for my first of the Asia Landmark series.

If you trust the meter reference and happy with it, just trip the shutter release button, and here you go, you got a photograph with proper exposure (don't worry, unless you are using slides, most modern print film have enough exposure latitude in tolerance of your mistake in exposure reading).

Shown at right is a typical focal plane shutter curtain for a SLR camera, it can be either horizontal traveled or traveled vertically to protecting film from fogging during viewing and metering; it will open during an exposure process (The span of time opens depending on your selected shutter speed); this combines with the aperture opening on a lens to form an exposure.

The correlation between shutter speed and aperture size is a direct one. Since both the aperture and shutter speed (forget about the elements of depth of field, action freezing or movement by blur factors) control the amount of light reaching onto the film. And since both double or reduce in a scale of one time (1X or 100%):
It means you can FREELY interchange the settings on shutter timing and lens opening for respective effects and YET retaining your preferred exposure setting.

Aperture value(s): f/64, f/32, f/22, f/16, f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, f/1.8/f1.4 etc. Control / adjust via the lens section*
Shutter speed(s): 1/8000, 1/4000, 1/2000, 1/1000, 1/500, 1/250, 1/125, 1/60, 1/30, 1/15, 1/8, 1/4, 1/2, 1 sec, etc. Control / adjust via the Camera section

*Referring to older manual focus-type SLRs only. Newer series of AF SLRs may have it controlled via camera body via Sub-Command Dial

For an example, let us just take an example with a scene of waterfall, the camera meter reading suggested a exposure of f/8 at 1/125 sec., your preferred effect is to freeze every single droplet of water to show the power of the waterfall, with a setting of 1/125, you may not achieve that kind of effect, but a shutter speed of 1/2000 may be able to convey that effect. Just set the camera's shutter speed dial to '2000' (1/2000 sec - just compensate it with five steps in shutter speed scale) with the reduction of light of five steps by open the lens aperture bigger by five steps; in this case, i.e. f/2.0. Now you are using a alternate combination of f/2 at 1/2000 sec. while the exposure is still equivalent to f/8 at 1/125 sec set earlier BUT the eventual effect of the photograph varies now with what you have envisioned to achieved. On the other hand, if the same scene needs to portray a sense of poetic movement, you may adjust the speed down to, let's say, 1/8 sec to make the waterfall have a sense of flowing water. The uncompensated figure for aperture might cause over exposure (from 1/125sec to 1/8 sec., there are four step down, more light will reach the film and cause overexposure).

nature flow.jpg
In this case, by adjusting the selected aperture to reduce the same equivalent amount of light to i.e. f/32 can retain the same exposure and yet achieve of what your desire - a free flowing waterfall.

Venice.jpg   The photo shown at left is another picture to illustrate an example of creative combination use between selection of a SLOW shutter speed with a flash to create certain visual effect.

Credit: Image courtesy of Mr. Jochem Wijnands ® Credit: Image courtesy of Mr. Manuel Angel Toral Fernandez®. images. Image copyright © 2005. All rights reserved.

If, for an instance, an exposure combination of 1/15 second on the shutter speed scale and an aperture value of f22 setting on the lens is needed, the aperture would get wider as the shutter speed increases. e.g. 1/15 sec at f/22 = 1/30 second f16 = 1/60 second f11 = 1/125 f /8.

Note:- Newer series of AF SLR camera that only has LCD display, the dial in front of the LCD is dedicated for variable apertures selection - such a design is commonly found on modern autofocus cameras.

Depth of field ("DOF")also plays an very important part of the creative segment in photography. It has a direct relationship with aperture value selected (the other two factors affecting depth of Field are being the focal length of the lens in use plus distance of the subject from the camera). When you understanding these factors, creative use of depth of field can add a lot of depth in your photography especially involve very much in the field of portraiture, travel, product and scenic photography. You can select a bigger aperture (Smaller number such as f2.0, f1.4 etc.) to throw undesirable background out of focus and thus put more emphasize on your subject of interest in a photograph. On the other hand, if the background of a scene is equally important or the subject is a group of people or objects at different distances from the camera where each one must appear sharp, a small aperture (f16, f22 etc.) can be used to make sure from near to far will appear in pin-sharp focus.

You MUST understand the compensated combination between apertures and shutter speeds in order to put them to good use. Most often, we always heard photographers complaining: "what turned out are different from what I saw inside the viewfinder during that moment...". Although it forms only a segment of how it can influence a eventual image, but you can get close to your desirable effect in your photography if you have a good knowledge of how each of these elements may affect your photography. Still confuse ? Let take an example, e.g. to throw all the undesirable background out of focus, select a larger aperture. We use a meter reading of f/8 at 1/125 sec. for discussion here, an aperture of f2 might achieve better result than a f8 for this purpose, but the selection requires you to compensate for the increase of light by four steps, it means unless you reduce the light by means of increasing the shutter speed to four steps in equivalent, your photograph will be over exposed. Thus, from f8 at 1/125 sec, the exposure is the same as f/2 at 1/2000 sec while you can have your background blurred out.

i.e. f/8 at 1/125 sec
= f/5.6 at 1/250 sec = f/4 at 1/500 = f/2.8 at 1/1000 = f/2 at 1/2000.

Lastly. after all this explanation; all you need to know is, for an example, a photograph taken at 1/4000 sec. and f/1.4 and one taken at 1/30 sec. and f/16 will have the same exposure value. However: the eventual effect in your photo taken with the respective choices on shutter speed selection (on camera) and/or aperture selected (on the lens) will be totally different.

A short Summary on the few sections in this site:

Shutter speed(s) (Duration/timing of the shutter curtain closing inside the camera section) :
It controls the degree of movement in your pictures (fast speed to freeze a movement or slow speed to create creative motion effect).

Aperture(s) (lens section) :
It determines the depth of field (zone of sharpness in front and behind) of the focus subject of interest. It adds depth and dimension in your photos.

Camera metering circuitry suggests an exposure (combination of shutter speed set in your camera + aperture selection on lens). User decides whether to override camera's metered / suggested combination for specific effect in the final image based on personal interpreation best expressing his/her thought.

It is so easy, isn't it ?

I do hope these can generate some interest for you to pursue further in photography.
still having Problem understand all these ?
Either beat me up or shows me what you had picked up thus far by rewarding me with a good picture or simply mail me ! 
(Probably my only e-mail contact you can find in my PIM site now but since you are still having difficulties, I permit you to reach me via email contact)

Introduction || about aperture || about shutter speed || about exposure || Glossary || Relative: Depth of Field


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