This article will hopefully help you understand the way to use the aperture on your camera lenses to get more light into the camera. In Part 2 we will deal with how aperture effects focus.At the heart of every camera lens is its aperture. It is the mechanism by which you, the photographer, let more or less light into the camera and together with the shutter-speed and ISO is one of the three cornerstones of exposure.
But use of the aperture, whilst pivotal in the process of getting light into the camera, goes far beyond just light-gathering; it is also the mechanism by which the photographer controls the depth of focus, or depth of field, in each of his or her images. Here then we will discover what aperture is and how you can use it to control light and focus.
The pupil is the aperture of your eye and, like your pupil, the aperture of a camera lens can be varied in size to let more or less light in. The first basic concept of aperture to get your head around is that the smaller the number [f/1.4 for example] the bigger the aperture, or ‘hole’.
Big number, little hole, less light. Simple. Well, a little bit back to front but simple enough once you know. One more time: small number, big hole. Big number, little hole. The diagram below should help get that point rammed home.
What does the ‘f’ stand for? Well, it doesn’t really matter but it helps to know that when someone says they used ‘f/8’ that you know that they mean the aperture setting of ‘8’ on the lens. The next little bit of jargon is the ‘stop’. You will hear this all the time, so now’s the time to learn what it means. First of all, people may say; ‘Which f/stop are you using?’ Translation?: what aperture setting are you using? So the ‘stop’ refers to the setting of the aperture. The next context in which you will hear the word ‘stop’ is when someone is asking you or telling you about a change in exposure. For instance, your pal has taken a picture that is too bright. He may say; ‘Hmm, I think I need to stop down’. Excuse me? Maybe if his pictures are too bright, he shouldn’t have stayed up so late, rather than needing to stop down.
‘Hmm, I think I need to stop down’ in translation means; ‘I think I should make the aperture smaller’.
Stop down: select a smaller aperture [bigger number].
So if you ‘stop down’ to let less light in through the lens, do you ‘stop up’ to let more in? No.
Oppostite of ‘stop down’ = ‘open up’.
With me so far? I hope so.
If you really want to know more about f-stops and the science of it all, read this excellent entry on the Wikipedia.
One more important thing about ‘stops’ is what amount of light is meant by ‘one stop’, as I am sure at some point you will hear people talking about ‘change the exposure by a stop or two’, or something similar.
What does this mean? Well, basically, if you have the camera set at an aperture of f/8 and want to ‘open it up a stop’ then you would turn it to f/5.6. If you wanted to ‘stop down’ by one stop, you would use the control on the lens to make the aperture smaller by one full click; i.e. you would turn it to f/11.
One ‘stop’ bigger [e.g. from f/8 to f/5.6] and the aperture is letting in double the light.
One ‘stop’ smaller [e.g. from f/8 to f/11] and the aperture is letting in half the light.
Confused? Well, first of all you might be saying: ‘Hey, wait a minute, my digital SLR doesnt have an aperture ring on the lens. I change the aperture with a little dial on the camera.’ This is a very important point and one further compounded, possibly, by the way you have the camera set up; i.e. do you have it set to change aperture in one-third of a stop increments, or by full stops? Finding this out will mean a little exploration in the menu of your camera but if you try and rememeber the following, it will help:
In the old days, cameras had a ring on the lens to change aperture. That ring was marked off in ‘one stop’ gradations:
1.8 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 and so on, but usually not much past f/32 on even the best lenses.
So these are your full stops. If you have the camera set at f/1.8 and want to ‘stop down three stops’ then you make the aperture smaller by three clicks; i.e. select f/4. If the camera was set at f/11 and you wanted to ‘open up three stops’, you would make the aperture bigger and select f/4.
Digital SLRs have made the job of understanding this a little harder by virtue of the fact that they are being controlled by the camera rather than by your fingers turning a ring manually. Meaning they can set the aperture size in many more gradations than just a full ‘stop’, usually in chunks of one-third of a stop. So on your digital camera you will find, on the display, apertures of f/1.6, f/3.3, f/6.3 and so on. These are thirds of a stop. You can, though, generally tell the camera via its ‘settings’ menu to allow aperture to be selected in full stops or in thirds of a stop. For beginners I would suggest setting the camera to control aperture in full, ‘one stop’ chunks.
I hope you are all still with me. This may all sound complicated and it is obviously more difficult to explain it on a web-page than demonstrate it in person….. and I havent gotten around, yet, to making little videos of myself demonstrating these things. That comes soon, when I have someone joining me in Japan later this spring, for a year, to work on this site and the business in general. He’ll be appearing in and I will be filming the demos; he’s cuter and younger than me
Combinations of aperture and shutter-speed and how changing one changes the other…
Although I will be writing a fuller explanation of shutter-speed, it is worth mentioning that changing the settings on the camera to let ‘one less stop of light into the camera’ is not just about doing it with the aperture controls. I feel a table of numbers is now in order…… and it makes the explanation easier.
First of all, we shall assume that the correct exposure for scene we are shooting is: f11 at 1/60th second. Here is what aperture corresponds to which shutter-speed with that exposure as the base.
All the combinations above will return a good exposure, even though we have opened up or stopped-down the aperture, or changed shutter-speed. Basically you can now see that halving the shutter-speed [making it twice as slow – 1/60th to 1/30th for instance] results in needing to make the aperture one ‘stop’ smaller. Remember what we learned about how much difference in light changing the aperture by a ‘stop’ makes?
- One ‘stop’ bigger [e.g. from f/8 to f/5.6] and the aperture is letting in double the light.
- One ‘stop’ smaller [e.g. from f/8 to f/11] and the aperture is letting in half the light.
Now, let’s add shutter-speed into the bargain:
- Halving the shutter-speed [making it half as fast – e.g. from 1/60th to 1/30th sec.] is the equivalent of stopping down the aperture one full ‘stop; e.g. from f/11 to f/16.
- Doubling the shutter-speed [making it twice as fast – e.g. from 1/250th to 1/500th sec.] is the equivalent of opening up the aperture one full ‘stop; e.g. from f/5.6 to f/4.
The faster the shutter-speed [e.g. 1/2000th sec] less light gets in. This means a bigger aperture. If the shutter is open for longer [e.g. 1/60th sec] more light is getting in, therefore you need a smaller aperture.
N.B. Remember that ISO is the third factor effecting exposure. Read our article on ‘Understanding ISO’ here.
Jargon used in this article or which you may hear on this topic:
- Stop – one, full click on the aperture ring of an older lens, e.g. f/8 to f/11. A stop’s worth of light is effectively half or double what was coming into the camera before you closed or opened the aperture, respectively.
- f/stop – the numbered setting of aperture, corresponding to its diameter relative to the focal length of the lens.
- ‘Stop down’ – to make the aperture smaller.
- ‘Open up’ – the make the aperture bigger or wider.
- Maximum aperture – the biggest size of aperture available on the lens [e.g. f/1.4].
- Fast lens – a lens with a very large [e.g. f/1.4] aperture.
- Slow lens – a lens with a very small ]e.g. f/8] maximum aperture.
- Variable aperture – zoom lenses typically have a maximum aperture of f/2.8 to f/6.3 through their range. A very fast zoom lens will be constant f/2.8 or f/2, which means the relative aperture will stay the same throughout the zoom range. A more typical consumer zoom will have a variable relative aperture, since it is harder and more expensive to keep the effective aperture proportional to focal length at long focal lengths; f/3.5 to f/5.6 is an example of a common variable aperture range in a consumer zoom lens.