In this next part of the tutorial series and moving on from ISO and Shutter Speed we are going to be looking at aperture and the affect it has on exposure. Some of you may already be aware that aperture not only controls your available light exposure but also your flash exposure (This is true of ISO also) but we are not getting in to flash yet, more on that much later on this blog.
The reason I want you to concentrate on just available light exposure and the fundamental exposure triangle (ISO, Shutter Speed, Aperture) is because I want you to get this nailed down before you go learning flash or buying that new camera or lens. Walk before you Run.
I have taught enough workshops in my time to of seen a number of folks wanting to do the next thing before they have the basics covered.
Let’s get in to aperture.
Aperture or F-Stop s it is sometimes called is that IRIS opening in your lens that kind looks like the Start Gate in SG1.
As we make a change to the aperture value we change exposure as well as DOF (Depth Of Field).
Concentrating on the exposure element, let’s walk through it. In the video posted below I walk through the effect of changing your aperture has on exposure. Also we have the aperture values in both 1/3rd stop and full stop laid out in a table.
As you can see from the table above you can change the aperture in 1/3rd or full stop increments and as it is with ISO and Shutter Speed to change a full stop you are making 3 clicks on your dial.
1/3rd > 2/3rd’s > 1 Full Stop.
As you open up your aperture from F8 to F5.6 (1 Full Stop) for example you increase exposure and as you stop down your aperture F5.6 to F8 (again 1 Full Stop) you reduce exposure.
Also as you increase exposure 1 stop you are doubling the amount of light and as you decrease exposure 1 stop you are halving it. (Exactly the same as ISO and Shutter Speed)
You can also make a change in 1/3rd stop increments, for example F8 to F7.1 is increasing exposure 1/3rd of a stop. Going from F8 to F9 is decreasing exposure 1/3rd of a stop.
A smaller F number F2 is a brighter in exposure than a larger F number F4 and it’s this that trips people up at times.
F2 to F2.8 to F4 to F5.6 - As the lens is stopped down from F2 through to F5.6 the exposure is decreasing getting 1 stop darker with each change.
F5.6 to F4 to F2.8 to F2 – As the lens is opened up from F5.6 through to F2 the exposure is increasing getting 1 stop brighter with each change.
F5.6 is darker than F2 and it definitely gives you more depth of field at the same focal length and working distance to subject. We will get in to Depth Of Field more in the future.
Aperture and Different Lenses
You will find that some lenses will have a different aperture range than others, for example a consumer zoom or kit lens will typically be a variable aperture lens, where a more professional lens will have a constant aperture throughout its range.
Variable Aperture Lens – aka the kit lens
A 18-55 kit lens will be a F3.5-F5.6 lens which means that if you are pulled wide at 18mm and at F3.5 and then you zoom in to 55mm the aperture is going to go from F3.5 to F5.6 on you and change your exposure 1 and 1/3rd stops. That may sound like a bad lens but they are just fine for getting started with, no need to go shopping yet. As long as you are aware of this lens trait you can work around it.
The aperture range will vary lens to lens but you will typically find it is F3.5 through to F32 and your constant common aperture in the focal range will be F5.6. this means if you set your aperture to F5.6 (or above) and find a good exposure for your photograph you can keep it at that aperture even when you change your focal length.
Constant Aperture Zoom – aka the pro lens
A higher end zoom lens such as a 24-105 F4 has a constant F4 aperture through its focal range (24mm to 105mm) which means as you zoom from 24mm to 105mm your aperture & exposure are not going to change on you. They cost a fair bit more than your typical kit lens though.
I have a couple of these lenses in my working kit.
Canon EF 24-105 F4 L IS which is a constant F4 lens that has an aperture range of F4 to F22.
Canon EF 70-200 F2.8 L IS is a constant F2.8 (1 stop brighter than F4) lens that has an aperture range of F2.8 through to F32.
With the above zoom lenses I can set any aperture that gets me a good exposure and it will stay until I change it. I have worked with variable aperture lenses before but personally I prefer either constant aperture zooms or primes.
Prime Lens – aka fast glass
We also have prime lenses, OMG I love prime lenses.
A prime lens is a fixed focal length and they are available in a wide range of focal lengths (14mm,24,28,35,50,85,100,135,200,300 etc). Primes are also regarded as fast lenses and when people say that they mean it lets in a lot of light (small F number). Where a more expensive zoom lens will have a constant aperture of F2.8 or F4 a prime can open up to F1.2, F1.4, F1.8, F2 depending on the lens.
I have a number of primes in my kit because I prefer shooting with them over zoom lenses.
Canon EF 35mm F1.4L II – This is a 35mm F1.4 lens and has a aperture range of F1.4 through to F22.
Canon EF 50mm F1.8 II – Plastic fantastic or nifty fifty. This lens is a 50mm F1.8 lens that has a aperture of F1.8 through to F22
Canon EF 85mm F1.8 USM – This is an 85mm F1.8 lens with an aperture range of F1.8 through to F22.
Canon EF 100mm F2.8 L IS – This lens is a 100mm F2.8 macro lens with an aperture range of F2.8 through to F32.
As you can see all but one of the prime lenses are faster than my zoom lenses. They let more light in.
We will get in to lenses in more detail in future posts and videos.
With the three exposure variables that we have looked at so far (ISO, Shutter Speed, Aperture) we have control over the exposure of a photograph and you can build that exposure by changing any or all three of these elements.
As we go forwards looking to learn about exposure I will show you how to do just that.
Remember that aperture controls your exposure but also has an effect on depth of field. If you are working with variable aperture lenses you have to watch for the exposure changing on you when you zoom in shooting wide open (F3.5 for example).
I you have any questions let me know in the comments below or on Youtube.
Thank you for reading.