Aperture and The Exposure triangle

The Basics Series for The Creative Pod The aperture is one of the three important aspects behind determining the exposure of an image, the other two being – Shutter Speed and ISO and together they form the Exposure Triangle. Before we get into the details of Aperture, it is first important to tackle two fundamental things about photography and lenses in general. 1. Photography is a play of light and shadow, in essence how much of a balance of light and dark areas you need in a photograph 2. How much of the area or field in front of you should be in focus I’ll explain the first point – With the aperture; you can control how much light is allowed to hit the sensor because that’s one of the things that an aperture does – its basically an opening in a lens that can be controlled to be wide or narrow so that the light passing through the lens is controlled very much like the knob of a water faucet controls the water flowing out. If the aperture is wide open, more light is allowed through and vice versa. The second point about the field of focus is little more interesting – is termed as the ‘Depth of Field’ or, how much of the area that forms part of your photo should be in focus. The lens is capable of keeping only part of the frame in focus as, by design; they’re built to be able to have portions of the frame in sharp focus and not all of it. That field of focus – can be imagined as thus – say you’re photographing a friend, its imperative that you will want to have her face in sharp focus but do you need that background also in sharp focus? What’s your subject here – your friend right, so the field where you focus for sharpness will be where ever she is while anything in front or behind her will be out of focus. Now how much of that field is going to be in focus is what Depth of field is all about. The other thing you need to understand about aperture is that they are denoted by an small letter ‘f’ against a number such a f1.8 or f11 or f22. The key thing is that – if the f-number is a bigger number like f22, the aperture opening will be smaller and if the the f-number is smaller like f2.8, the aperture opening will be wider. The f=number and the aperture opening has an inverse relationship. Do not forget that. Now lets deep dive into the bit about how it controls how much light hits the sensor. As we have talked about this earlier – The aperture is an opening in the lens which can be made to either be wide open or narrowed down. This is what controls the amount of light ultimately coming out of the lens towards the sensor. So going by what we just discussed earlier; if you set your aperture to something like f1.8; you are letting in a lot of light but if you set it to f10; the aperture has been closed down considerably and so less light is passing through. If you’re wondering how does this help you get a good photo of your friend; well think about it like this. If you are in a darker area, say indoors, you obviously have limited light as compared to being outdoors on a bright sunny day. In such a case; we now know that the aperture controls how much light gets through to the sensor so it makes perfect logical sense to then ensure that you set the aperture to its lowest f-number and remember, the smaller the f-number; the bigger the aperture opening. This way you are ensuring that you’re letting out as much light as the lens can allow to hit the sensor and expose the image. While we spoke of opening the aperture to its widest setting; we will now also be dealing with another consequence of opening the aperture wide open – the change in the depth of field or how much of the field before and after our subject will be in focus. Lets go back to the example of taking a photo of your friend and say you are focusing on her eyes. The depth of field for a f1.8 lens (ignoring the sensor size for simplicity) could be anywhere from the tip of her nose to her ear. While anything in front of her nose and behind her ear begins to lose focus and starts to get blurry. But lets say you have a lens that is just f4 at its widest, which is much less that f1.8 – The depth of field will be not as shallow since the opening is not as wide. In this case the field will be deeper and anything from say half a foot in front her nose and behind her ear will also be in focus, assuming you are still focusing on her eyes. The key point here is that a lens will not focus squarely on a single point alone and keep only that point in sharp focus but will have a bit of a range that it will keep in focus and that range is what is termed as ‘Depth of Field’. Now to sum up – a small f-number means wider aperture opening that allows more light to hit the sensor which also means a shallower depth of field or the area in front and behind the subject you are focusing on is much smaller whereas a bigger f-number means that a narrow aperture opening and also have a deeper depth of field. Here is an activity – Guided shot – 1. Switch on your camera and set it to Auto mode 2. Take a picture of a mug or a book, anything that is at least 10 cm tall 3. Ensure that when you take the picture; you are having the camera at the same level as the subject 4. You should be able to not only see the subject but also quite a bit of the background 5. Once you take the picture; make a note of the following: a. Aperture b. Shutter speed and c. ISO Manual Mode shot – 1. Set the camera to ‘M’ or Manual mode now 2. Set the shutter speed and ISO to what you noted down from the picture you just took from the Auto mode 3. Dial in an f-number different from what the Auto mode setting was and take a picture 4. Now dial in a different f-number and take another picture 5. Repeat step 4 will you exhaust all the f-numbers you can take a shot on 6. Ensure to not change the shutter speed and ISO at all as you repeat step 4 to maintain consistency and isolate the effect of the aperture Download the images on to your computer and you will notice that the relation of the f-number with the amount of light and the depth of field is quite evident. It can be a little tricky though as the images get darker so does the background get slightly less blurry so its good to repeat this under different lighting conditions. Check out the image at the end of this blog for how i did this same activity. When I was trying to get my head around the exposure triangle I decided to understand the aperture first since I loved the out of focus background in several portrait photographs and that blurry background was something I really wanted to achieve. After watching several videos and reading many blogs I knew that this is what I should be chasing first. In the next episode we will cover another point of the exposure triangle so stay tuned for more and please let me know about your feedback or any clarifications; I’d love to address them.

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