View Full Version : Exposure: A simple guide

29-07-2012, 10:36am
With all the features on your camera, there are really only three. When you use things like Scene modes, they are just preset variations of three camera settings that help ensure you get a good result. In Auto-Mode, you camera makes an evaluation and adjusts these same three settings. You might have a myriad of dials and menu options, which you can pick and choose, but these are often only simplifying the same three settings again!

What are these three camera settings that are the basis of all photography. They are the shutter speed (the time which your camera's shutter is open and your sensor, or film, is exposed to the light reaching it through the lens. The aperture, this is the diaphragm within the lens that can be closed or opened to differing sizes to control how much light hits the sensor, and the final one is ISO. ISO is the sensitivity of your sensor or film to light.

So using these three settings alone, you can basically achieve everything your camera does in auto, semi auto modes, and below is what each one does

Shutter Speed

The shutter speed controls how long the light coming through the lens apertures is allowed to hit your film/sensor. Slow shutter speeds can be minutes, seconds, or some of the lower fractions of seconds, like 1/2 a second, 1/4 of a second. Fast shutter speeds are usually very fast, like 1/1000th of a second. The faster the shutter speed, the more movement is frozen and the sharpness of moving objects will be increased. A guideline is that you can generally hand-hold your camera for a shutter speed that is the inverse of the focal length. So if you are shooting with a 200mm lens, then 1/200th of a second should allow you to hand hold your camera and get a sharp photo. Shooting at slower shutter speeds either requires a very steady hand or some sort of stabilising (a tripod). Slower shutter speeds allow blur (like moving water effect).


Aperture lets you control the diaphragm in the lens, thus how much light hits the sensor/film for a given shutter speed. Apertures are fractions. So aperture f2.8 is larger (more open) than aperture f22. These are really 1/2.8th and 1/22nd. So 1/22nd is smaller than 1/2.8, thus an aperture of f22 is smaller than f2.8. An aperture of f2.8 is bigger, so will let more light hit the sensor/film for any given shutter speed than will f22. This is apparent for all aperture selections : f4 is smaller than f2.8, but bigger than f8. The more open you aperture, the less the depth of field : distance, front to back, in your photo that will be in focus, outside what you focus on.

So a photo taken at f2.8 will have a shallower area of your photo that is in focus compared to a photo taken at f22.


ISO is the camera's sensor (or film) sensitivity to light. Low ISO's like 100 and 200 are less sensitive to light than ISO 800 or 1600. Lower ISO means less noise or grain in your photo than higher ISO's. As you go higher and higher with an ISO, the more noise/grain is visible in your photos. As you increase the ISO to a larger number and make your sensor more sensitive to light, it means you can use a faster shutter speed.


To get a great photo, you need to decide what your photo is going to look like, before you take it, and then adjust the above three settings to get the result you want. All three settings above are not independent, but they can be independently adjusted. Changing one without changing the others may not get you the photo you want.

Say you want to get a slow milky water effect, you need a slow shutter speed, but just adjusting the shutter speed and nothing else might result in your photo being over-exposed. So you set your camera to 1/2second shutter speed cause you want to show the blur of the water, but then you will likely need a smaller aperture (larger number) otherwise the amount of light hitting your sensor could be to much and you end up with pure white areas with no detail in your photo. So with 1/2 second shutter speed set, you can close down your aperture to say f22 to reduce the light through the aperture in the lens.

It is getting late into the afternoon and you are shooting kids sport. You are using a fast shutter speed to freeze the action, say 1/500th of a second, but as it gets darker, your photos are coming out dark. You can increase your ISO from 100 to 800 to increase the sensitivity of your sensor to light, thus getting shots that are not so dark.

See how all three settings work together to achieve the result you want/need. Learning how Shutter speed/Aperture/ISO inter-relate is the basis for all photography. So come to grips with how they work and interact with each other, and you are on the way to understanding your camera more fully and being able to make educated choices in relation to camera settings, to get the photo YOU WANT!

29-07-2012, 4:16pm
STOP Press.
(Humbly added as simple stuff for some, perhaps of some use to others.)

A useful means of understanding the relationships between the three controls: Shutter Speed, Aperture, and ISO is by the use of "exposure stops".

(Aside: I think that "stop" comes from the fact that these controls have usually been click stops.)
The connection between all three is that:

A doubling/halving of the shutter speed is equivalent to one whole (main) f-stop and is also equivalent to a doubling/halving of ISO value.

The three exposure stops below are all equivalent:

1/250 sec, f/11, 100 ISO

1/500 sec, f/11, 200 ISO

1/1000 sec, f/8, 200 ISO

(That's all.)

29-07-2012, 4:26pm
The Library!!



29-07-2012, 5:18pm
I like the following explanation of the "Exposure Triangle"


I hope it is useful to you.

29-07-2012, 5:54pm
In that explanation above, I don't get the relationship of their analogy to the ISO. They use quantity of water to represent ISO. But that just doesn't work ... a wide bucket for a short time, and a narrow bucket for a longer time may well collect the same quantity of water irrespective of ISO. It doesn't work. In their equation, only two parts of the triangle are needed, but there are three. They need to add a sponge to the bucket, and vary how ABSORBENT that sponge is. A sponge that soaks water up fast, versus a sponge that soaks water up slowly, and the final result is the quantity of water - NOT IN THE BUCKET - but the quantity that is in the SPONGE.

My very poor understanding of ISO is really really roughly analogous to how quickly the sensor can respond to the light that is hitting it. Hence why an ISO that can respond very fast, will make up for less light getting in, because it responds quicker to the light that's there.
So now to finish off their analogy so that it actually works with all three parts of the triangle ... you look at Width of bucket (aperture) and length of time in the rain (Shutter speed) and absorbency of the sponge (ISO) and the final result is to measure how much water is absorbed by the sponge (your final photo).
So more water in the bucket by being a longer time in rain, or more water in by using a wider bucket, is then further adjusted by a more or less absorbent sponge, and the final result is the water that is absorbed.
A sponge that absorbs water really quickly will pick up much more of the water that comes in - even if that's not very much water. But a very slow sponge that's made of less absorbent material, will pick up very little water, no matter how much comes in.

Anyway, I may be totally wrong here. And I'm happy to be told so.

04-08-2012, 8:36am
I think exposure as well as metering is one of the most discussd topics in Photography as far as questions and tutorials go would i be right???...
I know i'm a tad thick and it took me awhile to get my head around it comfortably to be able to either look at a scene and part guess the exposure via the sunny sixteen rule or via the cameras metering system.
I try look at it this way and try explain it to my Children whom all like Photography as well and that is.
(1) Keep apperture for controlling your depth of field as well as how it effects light to your sensor.
(2) Shutter speed by how much light it allows to your sensor.(light over time)
(3) And ISO , how sensetive you allow your sensor to become to light.
Hence your exposure triangle .
Yes it is important to do the math regarding the stops of light between speed and apparture for knowing how much extra light you will allow to effect the sensor whether it be via the shutter speed ,aperture or ISO but for the beginning try keep it as simple as possible ,if possible:) and keep it to those three mentioned above .
For me what i mostly do and hope i am on the right track is first look at my subject and decide on apperture of the scene to attain the depth of field i wish as well as take into account the sweet spot of my Lens (Twice the max or widest apperture of that given lens or by trial)..
Say i pick on a Landscape and pick f11 for instance in manual mode...I then next point my camera at a nuetral area of my scene being green grass or a blue sky( other neutral points of interest can be the palm of your hand etc).
This will be depending on your subject & if i pick the blue sky i will meter my cameras meter dial to zero on that Blue sky and then point my camera at the nearest cloud if one exists:) and see how far out the needle/pointer on my meter has moved off centre and adjust accordingly with my dial to bring that needle / pointer back to a stop over or under depending again on the scene and how bright or dark the scene may be. Normally good for horizon or seascape shots.
Metering off green grass or green folliage for a lanscape scene, say a mountain etc i do the same. Zero my meter of the grass then point my Camera at the scene i wish to photograph and see how far to either side my meter has moved and dial an adjustement accordingly for that first shot.
Now where does shutter speed and ISO come into this??..
Well as we know for starters your shutter speed for a nice sharp image is advantages to be as near to or above the focal length of the lens used ey??? and for Birding or moving object much faster so once we have metered as mentioned above we look to see if our shutter speed falls into that arena or as we are metering shoud i say.
If we can attain that shutter speed easilly enough at a low ISO (to avoid grain/noise in our image) Good!!.
If not then this is where ISO comes into the equasion by bumping up ISO we make our camera sensor to light more sensative and can attain faster shutter speeds..
App Priority mode takes a lot of the mucking around out of the equasion by allowing you to select the Apperture and it selects the shutter speed mostly and all you then have to do is toggle your exposure comensation or ISO if it cannot get the speed you wish.
If you take the time to do the math on app,shutter speed and ISO then the Sunny Sixteen rule can be used quite comfortably as a guide to suss you scene out and get an aproxomite starting point in your head of where to set up your camera to start off with.
My keep it simple take on metering and would like to be corrected if i'm out of kilta here:)...

04-08-2012, 9:21am
In that explanation above, I don't get the relationship of their analogy to the ISO. They use quantity of water to represent ISO. ...

It's an over simplified analogy.
This item is more correct http://www.ausphotography.net.au/forum/showlibrary.php?title=New_To_Photography:Detailed_explanation_of_ISO

05-08-2012, 10:58pm
So my improvement on the analogy by likening the ISO to a variable-absorbency sponge collecting the water isn't an improvement?
Mind you, ideally since a camera doesn't store any light once the shutter closes, to make this analogy work, the bucket would have to have no bottom, so that once the "shot" is taken (the bucket is removed from the rain) no water continues to soak into the sponge. The excess water needs to be lost just as the excess light is lost if the ISO was too low.
Hmmmm... Maybe the analogy is getting stretched a bit too far now - like all analogies really.