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What is an "aperture" ?

Aperture is referred to the lens diaphragm opening inside a photographic lens. The size of the diaphragm opening in a camera lens REGULATES amount of light passes through onto the film inside the camera the moment when the shutter curtain in camera opens during an exposure process. The size of an aperture in a lens can either be a fixed or the most popular form in an adjustable type (like an SLR camera). Aperture size is usually calibrated in f-numbers or f-stops. i.e. those little numbers engraved on the lens barrel like f22 (f/22),16 (f/16), f/11, f/8.0, f/5.6, f/4.0, f/2.8, f/2.0, f/1.8 etc. Each of this value represents one time the amount of light either more or less in quantity. Meaning to say, f/16 will let in 1X the amount of light than a diaphragm opening of f/22 and so forth; while on the other hand, an aperture of f/4.0 will let in 1X lesser than that of f/2.8 etc.

Diaphragm.jpg Loading...
Note: the diaphragm blades inside this manual focus Canon FD lens control the amount of light passing through the lens that eventually hitting to the film during an exposure process. The 'amount', or simply explained in layman term - opening changes according to selection of aperture (f/number). In this case, it is indicated by the f-numbers that imprinted on the lens barrel.

LENS SIDE:- If a simple word "diaphram" can be confusing to you, just try to think numbers engraved on the lens barrel are NOT referred to aperture diaphragm BUT rather, there are just number to let you refer the size of the lens diaphragm. So, if you are new to this, just memorize these numeric settings that will do, as they represent the corresponding size of the lens diaphram inside the lens and let you determine and control how much light you would require to let into the camera for a proper exposure by way of selecting an appropriate aperture diaphragm from large to small (lens opening). But technically, these numbers refer to the relative physical opening of the lens diaphragm. So, don't worry about the confusing part of them.

NOTE:- When you are one level up:- *.. These numbers are very significant to the lenses because they are calculated based on the properties of the lens they're on. f/5.6 on a wide angle lens will not have the same diameter as another, say on a long lens. There are simple lens formulas which help calculate the different properties. But the f number diameter is unique to each lens..". Benoit Aubry (benoit_aubry@hotmail.com but I would rather teach a new budding photographer whio may be interested in picking some pieces rather than serving technical request of a more seasoned photographer. But ant=yway, thanks, pal.

Modern Autofocus SLR cameras may have a different ways in manipulating the aperture. One of the trend is - the aperture value is now control via a thumb wheel on the camera (usually near the shutter release button) and the AF lens has no aperture ring to alter the value. Each camera manufacturer usually has their own series of lenses under a trade name to verify its usage, various compatibility issues with their previous camera model's function etc. For an instance, Canon manual focus lenses are called "FD" or "FL"; while their newer series of autofocus lenses (AF) designed for their Canon EOS Series cameras are referred as "EF" (Electro Focus). Each of these MF/AF lenses has their own respective way to illustrate the control of aperture in the camera. When you turn the aperture ring on a lens to vary the aperture, you will be able to check visually the set opening of the lens diaphragm (Opens bigger or stopping smaller). * here in this section, I am confining the discussion within the MANUAL FOCUS lenses ONLY because the proportion of used equipment forms the basis for a cheap, easy entry for potential new serious photographers.

* Some lenses such as those made by Canon (See above), the lens diaphragm will not react to turning, unless you press the aperture pin.
pentaxlens.jpg Nikonlenszm.jpg zuiko.jpg
There are many camera brands out in the market, thus, it is indeed very difficult for me to compile all of the labels into a single site. Anyway, I am using three popular camera brands to illustrate the whereabouts of these aperture on the lens. (A) is a typical FA lens by Pentax; (B) is a typical manual focus Nikkor zoom lens from Nikon; while the (C) is a Zuiko lens by Olympus.

Reminder:- the key to an theoretical good EXPOSURE = Aperture + Shutter speed

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. (WE ARE HERE) Control 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 via the Camera section

Remember: For a theoretical "perfect" exposure to be formed i.e. nice colour balance, every details shown or simply a photo that you are happy about, take a good combination between using an aperture with the appropriate matching shutter speed for any given film speed (ASA/ISO) are required. The latter refers to the film speed of the film roll used. i.e. ASA 100, ASA 200, ASA 400 etc. the faster the film speed used, you can use to capture lower lighting situation but at the expense of grainer output of prints / slides. Next, a little confusion may create for you to learn here: - each step increment in the use of film speed will also indirectly correspond with one step of aperture OR shutter speed.

I know you must be asking a mind boggling question while you read until here: Ooi....HOW THE HELL WOULD I KNOW WHAT APERTURE TO SET on my lens when I take a picture ? Frankly, you need not have to ! Inside any modern camera, there is a metering cell residing internally which measures the light intensity of the scene you are trying to capture/pointing to. Its metering circuitry will SUGGEST an exposure for you. For an instance, the exposure suggests by the camera's internal metering circuitry indicates 1/125 sec. (camera) with f/8.0 (lens) will deliver a decent exposure for your intended capture. You can override the camera setting (depends on whether the camera has such option for you to manipulate the aperture on the lens OR shutter speed on the camera, most P&S don't offer such options but a SLR camera usually does). For an example, change the f/8.0 to f/4.0 (let in more light by 2 steps 4.0-->5.6-->8.0) and compensate the shutter speed by few stops by limiting light entering the camera shutter i.e. 1/125--->1/250--->1/500. The compensated 2 steps on the shutter speed still delivers the SAME EXPOSURE as the earlier camera suggested reading. The difference is now with a f/4.0, you can achieve a narrow Depth of Field (refer to below WHY and WHAT difference it will bring to your picture with such alternation)..

However, the MOST confusing part for any new photographer is: Just remember in photographic term: a BIG aperture is actually referring to a smaller number engraved on the aperture ring of the lens i.e. f/1.4, f/2, f/2.8, f/4.0 etc. while small apertures mean bigger numbers i.e. f/22, f/16, f/11, f/8 etc. Once you have "overcome" such "mental block" in calculation, it should help you greatly understand / enjoy reading more in other sections that follow. So, it is important that you OUGHT to digest this paragraph. (CLICK HERE to understand the relation of those numbers found on the lens where how the lens diaphragm inside at each aperture set. Well, I am not sure who was the hell was the bloody smart guy who first started by inverting the number on the aperture on the lens - where small number (f/2.0, f/2.8 etc.) is actually referring to a larger lens opening while big number(s) such as f/11, f/16, f/22 etc. is actually smaller aperture. Basically, large aperture (f/2.0, f/2.8 etc.) lets in more light to the camera shutter for an exposure, while small aperture (f/11, f/16, f/22 etc.) has a smaller opening in the lens diaphragm to let in LESS light for a given exposure. The confusion usually causes a beginner who might be poor in mathematics gives up serious photography from here @#$^*#&*!!. Well, I guess you are not within that figures-fophia group, so - why don't just be patience and spends a few minutes to DIGEST this part. Trust me, it worth the time and could reward you with plenty of joy with the camera you own.

About aperture and its direct relation that might affect in your photography:- i.e. Other than controlling the amount of light entering into the camera, What else does "apertures" do ?

When the shutter button is released, light passes through the aperture diaphragm and hit the film, an exposure is formed. Basically, aperture, along with duration/timing of the shutter curtain opening, BOTH contribute to a the formation of an exposure. But aperture also affects an important photographic element called "depth of field" (short form "DOF"). You may ask, what is hell is this "Depth of Field" ? Depth of field is just technical term used to describe the 'zone' of sharpness' between nearest and furthest of a subject in focus (to be more exact, distance of sharp focus in front and behind, subject on which the lens is focused).

There are a few elements that will affects Depth of Field in a picture
Note:- Factors on lens ONLY, shutter speed never affects depth of field):

  1. 1 the lens opening (diaphragm inside the lens)   the bigger the apertures used, the zone of sharpness is shallower or vice versa i.e. smaller aperture used will has extended depth of field
    2 the focal length of the lens (50mm as standard, 80mm above as telephoto; 35mm or shorter as wideangle)   wide angle lenses have extended field of sharpness than a longer focal length telephoto lenses and/or longest reach focal length on your zoom lens), and
    3 the distance from the lens to the subject   the nearer the subject is, the shallower the zone of sharpness and vice versa.

frame.jpg <<--creative use of picture frame in composition and small aperture to gain maximum depth of field.


PhilipChong (41k)

Shallow depth of field with combination of close focus with a telephoto lens and a fairly large aperture may limit the zone of sharpness to minimal.

MORE illustrations

MC Lau (

Top and Bottom:- Typical scenic pictures with a smaller aperture to gain extended depth of field (sharp zone of focus)


PhilipChong (44k)

Lovely blur out (depth of field) on distracting background via use of a combination of telephoto lens with a large aperture which draws viewer attention to the main subject.

CY Leow (52k)

In fact, if you still don't understand, just memorize this: Other than it can be used to regulate amount of light entering into camera for an exposure, aperture also will affect the degree of depth of field. When combined with other essential elements that may also contribute to depth of field changes, such as focal length of the lens in use, the distance of your object in focus, you can make use of depth of field for creative control in your photography. For example: use larger aperture (Smaller number like f/2.8, f/2.0 etc.) with a long focal length to isolate or emphasis on expression, such as in portraiture photography; or use a smaller aperture (Bigger number like f/16 or f/22 etc..) to ensure pin-sharp details in both the foreground and the background.

Another factor you need to know is: All the markings on the lens barrel are double in effect . i.e. f/11 doubles the amount of light of f16, f2 allows 1X more light than of f2.8 does into the camera etc.

With a mechanical SLR camera, with the proper exposure GUIDE suggested by the built-in meter in a camera, you need to adjust both aperture and shutter speed yourself (it is termed as "MANUAL" setting in an automatic camera). Usually in the case of an automatic camera, you will still have manual control operating as if you are using a mechanical camera. Typically, a few extra choices of exposure control methods may be provided:- the first is called "Aperture Priority" (some camera uses a symbol "Av" - short for "aperture value"; the next is "Shutter Priority" (Tv - short for "Timing value". Aperture priority means you select the aperture to determine the depth of field yourself and the camera will set to the appropriate shutter speeds to match your aperture selected for a optimum exposure suggested by the camera's built-in electronic metering circuit, while shutter priority will let you select the preferred shutter speed setting and the camera will select the matching aperture values to match your choice. The third option is called the "Programmed Mode"(P - short for "Programmed Auto", where the camera select both the aperture value and the shutter speed for you and you may have no control in determine the depth of field yourself. (some cameras offer a another mode called flexi-program - I think it is too complicated to explain here).

Some examples of how an APERTURE PRIORITY AUTO SLR-type cameras shutter speed ring look like
and comparison made with a fully mechanical SLR type (below - far right)

Nikon F3

Nikon FE2

Nikon FA

Nikon FM

Nikon F3
Top Av auto SLR models of yesterdays: -Other examples are:
Pentax LX

Nikon FE2
Other examples like the Olympus OM2n and Canon AV-1

Nikon FA
This is a Multi-modes auto SLR. The ring doesn't have an "A", various modes ae at the side P, S, A and M (Manual)

Nikon FM2n
The Shutter Speed ring of a MECHANICAL / NON-AUTO SLR. no Auto selection button or setting. You need to set the shutter speed on the camera section along with the aperture on the lens. Other brands such as Pentax offers K1000, Olympus has an OM-1 etc.

Canon SLRillus.jpg (15k)
Newer range of autofocus SLR cameras use a new method of controlling aperture. You will find there is NO NEED to set aperture via the lens aperture ring; instead - aperture is controlled by the thumb wheel for BOTH shutter Speed (B) and Aperture (A). A method first pioneered by Canon on their manual focus Camera, the Canon T90 back in 1986. Although this new electronic input method is different from older SLR cameras, the principle remains the same. The VISIBLE confirmation of the selected aperture used on camera like this type is via the LCD on the top panel OR through the viewfinder.

Note: An exposure control ring found in many modern SLR. The various setting may be represented by a few symbols/letters, "P" is for "Programmed AE", the "Tv" is for shutter priority while the Av (aperture value) is referring to aperture priority - Canon's way of interpreting in their A and T series camera bodies. IF you are a owner of one of those SLR cameras, you can CLICK HERE to find out the exact model you are using. While Nikon Owner may use THIS SECTION OR you may find the specific camera models that I might have developed with a featured section.

Every camera manufacturers have different design of how to adjust shutter speeds with a dedicated AF lens. For an example, Nikon's Nikon F5, 1996/7 finally followed Canon's path in using wheel input for shutter speed and aperture control; followed by its next generation AF film/digital-based SLRs which resulted in newer AF G-series Nikkor lenses now has NO aperture ring on the lens barrel for controlling aperture. However, if an older manual focus Ai lens is used in manual or aperture priority AE mode, it will still operate as an conventional SLR in which you will still make use of the lens aperture scales. Time changes, methods alter but basic principle remains.

I strongly advise you to consume this section first before you think of proceeding to the next segment on shutter speeds. If you can't ,or finding difficulties digesting what I have prepared here, I'm sorry for my failure in explaining the essentials. In such cases, I would suggest you to buy a better illustrated photographic reference book or join a local photographic club. But if you do understand and have picked up something from this section, you are encouraged to click at the button underneath and continue...

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


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