Photography Tutorial 02 (Understanding Aperture)

February 07, 2013  •  Leave a Comment

Time to learn about Aperture in photography. Commonly also known as f/stop.

But first a quick recap of the previous tutorial, which I laid the grounds for understanding the capture of light through the lens and we explored mainly the function of SS (Shutter Speed). The longer you leave the shutter open (the slower the time setting) the more light filters through the lens. This is one of the main variables to control light. And I did mention also that Aperture is the other one. Which allows light through and controllable but using the diaphragm of the lens. Larger or smaller opening. 

To finally cement this concept let me give you an analogy. You need to fill a container with exactly 1 litre of water from a tap. Now you can achieve this in two ways, either by opening the tap fully wide open so you get the 1 litre in a fraction of a minute pouring through or you can open very little and let the water drip but then you will need a longer time to finally get the 1 litre.

Once you know the causes and effect of both, the Shutter Speed opening longer or shorter time, and the Aperture (diaphragm) opening wider or narrower both with the same common purpose, to achieve certain amount of controllable light filtered through, then you can go and adjust both and find a level that suits your purposes.

So we have learnt that leaving the shutter speed opened for longer makes it susceptible to shake, so you want it high enough to leave you comfortable shooting.

Queue in Aperture, which allows you opening of the diaphragm, and you can adjust it to work alongside the Shutter speed to achieve the desired exposure of the subject. Remember again that with Aperture the numbering system is the reverse, the smaller the number the wider the opening of the diaphragm. And they typically go like f/2.8 is wider than f/4. And f/4 is wider than f/5.6 and so on. These numbers are fixed and they are arrived through a mathematical formula and I will avoid going into those details, suffice for you to just remember the numbers and that f/2.8 has a diameter opening which is double of f/4 and that f/4 has a diameter opening double of f/5.6. Which consequently having double of the opening allows double the light through.

Visualise in your mind Shutter Speed = how long you will leave the water tap open. And F/stop = opening of the tap, you know that thing that we do when we open the tap and we let the flow of water out, sometimes we feel oh I can twist it open more, and then a bit more but suddenly you overdo it and off comes the splash of water from the sink and sprinkles through.

So we have learnt the result of opening the Aperture wider (remember smaller numbers means wider opening) is more light allowed through. But I hear you ask "So why don't I just stick the aperture to the lowest number (widest opening) and hey ho! I am no slave of the shutter and am not restricted any more."

The thing is, and apologies here as I cannot resist a malicious grin implying I had a card under my sleeve to get your full attention again without jumping off the gun. Aperture affects DOF (Depth of Field). Affects what??? I hear you say again :).

Yes, there is a little thing called DOF (Depth of Field) which to some extent every photographer who knows about this struggles and has to play ball with it. Its not always a bad thing, it depends upon what you are trying to achieve, and the quicker you have a grasp on this little photography beast the faster you will start understanding what is going on with your images. You know those results that often seem like your image has a shake? Many a times this is not the shake but result of a shallow DOF. The smaller the number of the f/stop (larger the diaphragm opening) the shallower the DOF. Put simply the shallower the DOF means that the plane of focus that you are able to acquire maximum sharpness on is very very narrow. This is best explained with an example. This image has a very shallow DOF, notice how just the front part of the image (focus plane) is sharp and fractions of millimetre back everything starts getting blurred.

And this has a sharpness that goes deeper on the image, this is achieved by increasing the f/stop number (closing down the aperture) f/8 will give you sharpness going deeper than f/5.6, and f/22 will be much better than f/11. The bigger the number the narrower the diaphragm and you are able to acquire a deeper plan of focus, sharpness which extends a bit more into your image (Landscapes typically are shot with narrower apertures so the focused areas extend deeper).

Time to jog your memory, so you see, you are getting a deeper DOF (sharpness extending deeper) but at a cost of light. Remember? Above I did mention that you might have wondered why don't we just keep the f/stops at the lower number to allow more light filter through? This is the reason. If you have a smaller f/stop number your DOF is so shallow that if you are shooting a flower you will not get all the petals in focus. So you compromise and try an f/stop slightly higher number to allow a bit more parts of the flower to be in focus also.

I do not want to confuse you a lot in this aspect at this moment but we will explore a bit more once you grasp the concept of Aperture and you start shooting and have an idea of what the aperture was and shoot again with a different aperture setting and notice the differences in DOF.

Now to finalise here are two things you can do to help you when shooting. If you want to try to get a deeper part of the subject in focus try to shoot through an angle that gives you a wider plane of focus, get into a position where you see more of the subject in one plane rather than viewing the subject through your lens in a way that only a narrow part is in one plane and the rest is further away. Secondly and more importantly, and this I will discuss on one of my next tutorials, when you step back the DOF increases. So if you are struggling with shooting a flower for example where you are getting just a very small part in focus and the other petals are out of focus, by stepping sometimes just half a yard back you will be increasing the DOF and you will gain that extra allowance and get more of the flower in focus, increased Depth of Field.

But remember also that DOF can be used to our benefit. You might want to isolate something totally out of its background, detach it. Then use the lower numbers, which will give you narrower DOF. And keep thinking always DOF when shooting. And remember focusing works in planes so if you are shooting a portrait for example or even a flower that you want it isolated, detached from its background, then find an angle that you see the background as far detached as possible from the subject. Shoot a portrait by asking the subject to step just a foot or two away from the wall or background and you will see that the result will be a beautiful blurry background rather than one that becomes almost part of the subject.

So you can use the aperture in many ways rather than just to allow light through. This is what Aperture does, besides allowing control of filtered light it also gives you control over DOF. Gives you that beautiful possibility of controlling the blurriness of the background,

Happy shooting and if you have any questions or comments please feel free to tweet me at @aminart



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