Everything you need to know About DSLR Cameras – Part 2/3
Understanding DSLR Cameras (For Beginners)
This is the second part of the three part series on Everything you need to know about DSLR Cameras. In this part we shall learn about some basic DSLR functions.
Note – Please read the sections on Aperture, Shutter Speed and ISO above after going through the details on Exposure
You will hear about the term Exposure quite often. Exposure is the sum total of light captured as a product of the aperture (f-number) and shutter speed (length of time the shutter remains open). Sometimes, it is also expressed as Exposure Value. It is possible to arrive at the exact same Exposure Value using different combinations of aperture and shutter speed.
As we shall learn shortly, aperture and shutter speed has an inverse relationship with each other. This is important to remember because you will need to be able to figure out how changing one affects the other in real life situations.
Basic DSLR functions: Aperture
We already have learned what Aperture is, even if it is very briefly. Aperture is a small opening on the lens that allows light to enter the camera. This opening is controllable and selectable, being one of the basic DSLR functions. You can select it manually or let the camera make the choice on the fly, depending on the shooting settings you select.
Aperture is expressed as a number. More specifically, it is referred as an f-number. So, you would have numbers like f/1.2, f/1.4, f/1.6, f/1.8, f/2, f/2.2, f/2.4, f/2.8, f/3.2, f/3.5, f/4 and so on. Aperture charts are available that express these in 1/3rd or full one stops. Meaning, each number increases or decreases Aperture in either one-thirds or full stops depending on the chart you are following.
The sequence of numbers that we mentioned above expressed Aperture progression in one-third stops. In full stops the sequence will read something like this – f/1.4, f/2, f/2.8, f/4, f/5.6 and so on.
On the full stop chart, every stop on the left denotes doubling of the Aperture. In other words doubling of the amount of light that enters the camera. If you slide down the right of the chart it reduces the Aperture (or the size of the aperture) and therefore the amount of light that enters the camera. Every stop denotes half the amount of light that is captured than the stop before it.
So, larger f-number means smaller Aperture and smaller f-number means bigger Aperture. Sounds kind of confusing? Don’t worry, you will get used to it.
We have already learned in brief what Shutter Speed is. it is the length of time the shutter remains open to allow light to come through. We have also previously learned that shutter speed is controllable and selectable. This is yet another of the basic DSLR functions.
You can allow the camera to control shutter speed or select it manually. Shutter Speed is expressed in fractions of second. So, you will read about shutter speeds such as 1/100, 1/200, 1/400, 1/800 and so on. Smaller that fraction, faster the shutter speed is. Larger the fraction, slower the shutter speed is.
So, you will also hear about, and later on use shutter speeds such as 1”, 2” or longer. Just like Aperture, every immediate fraction on the above scale reduced the amount of light by half. Every fraction preceding doubles the amount of light.
Inverse relationship Between Shutter Speed and Aperture
We have referred to this before on this guide. Aperture and Shutter Speed has an inverse relationship between each other. They both do the same thing, increase or decrease the amount of light that enters the camera. Thus, increasing any one of them will have the same effect as increasing the other.
Alternatively, it also means if you want to collect the same amount of light, you can increase one and then decrease the other by the same factor. Let’s understand this in more detail.
Let’s say that Aperture f/4 and a Shutter Speed of 1/100 you get X amount of light. You need to increase the Aperture for some reason but you want to retain the same amount of light. You know that Aperture and Shutter Speed are inversely related. So, you increase the Aperture by (let’s say) 1 stop to f/2.8.
But now, the amount of light increases. You risk washing out your images. To compensate you increase the Shutter Speed by exactly one stop. That means you bring it down to 1/200. Increasing the Shutter Speed reduces the amount of light and compensates for the increased Aperture.
Now that you know how these two parameters are interlinked, you are in a position to alter both and yet be able to achieve the same Exposure. Let’s say that in the above example you changed the Aperture Value to f/2.8 and increased the Shutter Speed to 1/200 sec. You could have altered the Aperture to f/5.6 and the Shutter Speed to 1/50 and yet achieved fundamentally the same exposure.
Acquiring focus denotes bringing a subject that you want to photograph in sharp contrast with its surroundings. It is one of the basic DSLR functions. In digital cameras this is done automatically. However, thanks to their versatility, you can switch to manual focusing and adjust the focusing point as per your choice by manually turning a focus ring on the lens.
There are tiny focusing sensors on your DSLRs. These are known as Phase Detection sensors. These are located towards the base of the camera depending on the make and model of your camera.
When light comes in through the lens most of it is redirected towards the pentaprism to power the viewfinder. But some of it is redirected towards the focusing sensors. These sensors help in acquiring focus.
The process itself is a bit complicated. Rays of light bouncing off of an object travel through the lens. Small focusing elements in the lens bend the light to make it converge on a point on the sensor. Thus, a sharp image is formed.
A secondary series of sensors known as Contrast Detection sensors are also present. These are used when the camera is in Live-View mode.
Live-view mode denotes when the reflex mirror inside the camera moves away from the path of the sensor and is locked in that position. You are unable to see anything through the viewfinder at the back of the camera.
The LCD screen becomes your composing window. The view that you see on the LCD screen is actually the view that the sensor sees.
Depth of Field
Depth of Field (DoF) denotes the extent of an image that is in acceptable focus. Any image that you make has to have a focusing point. That is the point at which the lens acquires focus. That point is the sharpest in the whole of the frame.
Now as you move away from the focusing point the image will be less sharp. Less sharp yes, but still acceptably sharp. But if you move even further, the image will be no longer in focus.
DoF is that area starting from the focusing point (the sharpest point) till the point where sharpness is acceptable, is known as depth of field.
DoF depends on a few factors. One of the primary factors is the aperture that you are using. We have already discussed in length about Aperture. Apart from the control of light Aperture controls the DoF.
Smaller the Aperture, more is the DoF. On the other hand larger the Aperture, less is the DoF.
Additional Aspects about DoF
Another factor that governs DoF is the size of the sensor. If the Sensor is large (like in full-frame cameras), you are likely going to get a shallower (less) DoF compared to a camera with a smaller sensor (let’s say a crop camera).
The third aspect that governs DoF is focusing distance. Focusing distance refers to the actual distance from your lens’ optical center to the point that you are focusing at. The further that distance is more is the DoF.
You would think that turning the focusing ring all the way to infinity would give you sharp corner to corner focus. But that does not technically happen. The reason is we are not looking at a flat surface. We are looking at a three dimensional scene in front of us and in that scene several objects are located at different distances.
Plus, the lens itself isn’t flat like a TV screen. It is curved. That is why it is optically impossible to bring into focus everything in a scene. In other words there is no way to produce a lens that could create an image that is sharp corner to corner.
The technique that most photographers adopt is that they focus about two thirds into the scene. That way half the distance from the bottom of the frame to the focusing point and all the way to infinity is acceptably sharp.
A word on Hyperfocal Distance
It is an intelligent way to achieve a vast depth of field, but not the best. The best alternative is to use something that is known as Hyperfocal Distance. Hyperfocal Distance involves using a complicated calculation that considers the focal length, sensor size and several factors to come up with the optimum focusing distance that would give the maximum DoF. There are calculators available online which you can use. Here is one link.
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