F Stops

When I started learning about photography, I was a bit confused about F stops. F stop, like a nightmare boomed up everywhere, leaving me perplexed. What were these numbers f 1.4, f 2.8 etc. As a hobbyist I always thought, these complications were not for me. It was not until I realized, the importance of the same. There were a lot of questions that were to be answered. What stepping down actually mean? What is stepping? What role does it play in exposure? and lot more than this. 

Starting with the most basic definition, F stops are nothing but a number related to the amount of light passing through the aperture. We are all aware of what apertures are. At least I'll assume this much. If we are not, then probably a revisit to the the this article will help.

Aperture

Looking at the picture above, we know what aperture looks like. In better lenses the hole that we are talking about has more blades as compared to 5 here. This will give the opening a more circular look not a pentagon as shown.
Let us assume that our aperture is a circular hole through which we allow light to pass. 

Now, aperture allows light into the camera. The wider the aperture, the more light enters the camera and vice-versa. 
If we talk about a f number, it directly depends on the light we allow to pass into the camera with respect to the opening of aperture. We put these f numbers onto a scale, called a f scale. Every number on a f scale doubles the amount of light entering the camera.

F Scale

Looking at the diagram above we get a clear picture of what f scale is all about. 

Let us think that the Diameter for a particular aperture is d mm. The area of circle for radius d/2 mm is "a". Now, to double to amount of light passed (double the area) ie. for 2a we need to multiply d by √2. Not getting into this too much, but we now know that if diameter of aperture is multiplied by 2 then the area of the aperture is double and hence double the light. 

Is that it? Is this how simple the f scale is? but then what does f 1.4 2.8 etc tells us. Where do these numbers come from? Definitely, there has to be something else that impacts the amount of light coming in.    

Looking at the above diagram, we can deduce that focal length plays an equally important role.

Therefore, if F is the focal length and D is the diameter of the aperture we can say that any quantity x = F/D. Rearranging D = F/x. Here x being the f stop number, D is the diameter and F is the focal length. 

Now lets say 
D = F/x.
If Area is to be doubled then D is to be multiplied by √2. To keep the equation balanced, we can say that x is to be divided by √2. 

Hence, if D is 20 mm, F is 40 mm then x is 2. To double the amount of light we know that D is to be multiplied by √2 and x is to be divided by √2. Thus, x now becomes 1.4 approx.   
Clearly, to open the aperture such that we allow double the light to be passed, we divide the f stop by √2, or if the aperture is to be opened so that it allows half the light, we multiply the number by √2.

Therefore, lets say for a aperture f1 if we need to half the amount of light we multiply by √2. The next aperture hence, f1.4. Looking at the table below wold ease up our calculations a bit.

F Scale Numbers

We know now how these numbers are arrived at. Also, we know the significance of these. Stepping up would mean increasing the f number to its next lower number. For example, if we are on f 4 and we realize that the  exposure is a bit on the darker side, we can step up by a stop (f 2.8) and correct the exposure for us.  

Hope the jargon is simplified know. We can say what f numbers are and how are they used. How is the scale calculated and read. Let me know if there is any issue understanding the same.

Exposure Value

We all had a discussion about a lot of things that related to Exposure. The three pillars - shutter speed, aperture and ISO were discussed. Ever thought how we could measure exposure and how can we quantify it.

Let us say if we have a scene to shoot. Now we chose a shutter speed to shoot the same. We keep an aperture that is in accordance to the shutter speed such that the scene we shoot is exposed properly. I suddenly realize that the shutter speed is to be increased for some reason and I increase it. Now we know that aperture will have to be widened here to accommodate the change in shutter speed. This is done to maintain the same luminosity of the scene. 

From the above example we can say that Exposure value (EV) is a number that represents a combination of a camera's shutter speed and f-number, such that all combinations that yield the same exposure have the same EV value (for any fixed scene luminescence).

Also, we can say that to achieve the same exposure value of a scene, there can be many combinations of shutter speed and aperture. Exposure thus can be said as the combination of shutter speed and aperture. Different combinations can lead to the same EV.

EV 0 corresponds to an exposure time of 1 s and a relative aperture of f/1.0.
Exposure value also is used to indicate an interval on the photographic exposure scale, with 1 EV corresponding to a standard power-of-2 exposure step, commonly referred to as a stop. There are a number of articles on the net that can give you the different combinations required for same EV. 

See below the combinations.

Exposure Value Chart

Once we read the above chart, we know that if we want an exposure value of 14 and we select shutter speed as 1/1000 then our aperture should be f4. Nothing, difficult here, all that we have to know is what exposure value is to be chosen. Then, we can select our shutter speed and aperture based on the chart given above. There are countless articles on the net that can display this chart. Take a print and keep it in your pocket for reference. 

The question that arises now is, how to choose an exposure value. Well, this is the difficult part here. You'll have to browse through a lot of tables on the internet. Follow sunny 16 rule, know about the light conditions and the subject you are shooting. There are tables for this as well on the net. Go through them and figure out what works best for you. This will surely need time, patience and skill for sure.

Exposure based on conditions

The table above will give you the details for selecting exposure value. There are certain conditions on which these are calculated. You'll find table like these on the net easily. 
For the sake of simplicity, I'll  explain that shooting a scene in heavy overcast will give you an exposure value of 12.
Referring to the table above we can deduce that if my shutter speed is 1/500 then my aperture should be f2.8.

We talked a lot about the exposure here. We devised a way for calculating the perfect exposure based on the scene we shoot. Always remember, this is a guideline and you should see if this is actually helping you to get your desired result. In most cases it should. But in cases use you knack to get the correct picture you want. We can learn a lot of stuff, but ultimately trust yourself with your instincts. There are many rules to photography which we'll eventually discuss. Learn them and follow them, but give your shot your treatment to create magic. There is a lot more to exposure than this but for know we'll close the discussion here and move ahead. We'll come back to this topic later on for sure.

Exposure in Photography Continued

Exposure was explained a bit in the previous article. For a basic understanding the article is a good and must read but do not take this that easy. Exposure is the crux of photography and creative usage of the same can actually create magic.

We understand from the previous article that there are certain ways in which we can control exposure. These are Shutter speed, Aperture and ISO. Always remember these are mere tools, creativity comes into effect when you actually use these for your requirements. we can easily control exposure using any of these tools or all combined. We'll covering the photographic effects of these soon. As we talked about the above three pillars, which are the basic fundamentals for exposure, there are still some concepts that are important to get your desired effects.

We all talked about proper exposure or perfect exposure. What exactly is a proper exposure? Not too much bright, neither dark. Is this what we mean by proper exposure? Or is exposure, just a sensory reaction to incident light? Lots of questions and heavily debatable topic. Since, the idea here is to be bit more simple and hence for our understanding I'll try to explain in much simpler terms.  

"In simple terms a properly or a perfectly exposed picture would mean capturing maximum possible details or information of the subject." 

Is that it. Is this all about exposure that we scream about. Yes, and trust me there are just three things that we have already discussed, that will effect the exposure. There are some important concepts that may not be effecting exposure (as one may debate), but these are worth a mention here. 

If we look at the picture we see that rocks under the water. When we clicked the image the idea was to catch the details under water. Since, the sky was bright and its reflection was making it impossible to catch the desired. Exposure could ensure the rocks came up. If we look at the rocks with our eyes then probably we would seen them correctly. But, the camera behaves differently. It does not have a very accurate recognition of the contrast range from black to white and hence, it involves a lot of electronic effort by the camera to get your subject correctly exposed.  This does not look very digestive at the moment but for now lets go with it.

Just to clear your confusion lets talk about this with a different picture.

The above picture was a bit difficult. Not getting too technical here, but even 
if you get the exposure correct still you may not get what you are looking for. If we want the sky exposed correctly, the bird would be completely black, silhouetted against the sky. If we expose the bird correctly here, the camera would do what it did to the sky here. 

Putting it simply, the camera has certain ways of ensuring that the subject that we are clicking is properly exposed. In some ways this adds to our advantage, but in certain ways it might work against what we desire. For example, clicking a scene in snow could be a challenge. The camera would want to lower the exposure as it is set against the snow. 
There are certain algorithms that the camera works upon to expose the pics you click. This is called metering. For your desired effect you would want to use correct metering that your camera has to offer. Metering modes are present in almost all cameras nowadays. We will detail out the metering modes later. For now, just understand that to correctly expose your pic (to your desire), a correct metering mode is important.

Another important concept is white balance. A very simple explanation would be that you may need to educate your camera about the light conditions around. You may need to tell the camera that you are clicking the shot in shade or in daylight or under clouds or in tungsten light or in incandescent light etc. Technically, by doing this, you are actually trying to ensure that whites in your scene are actually white.
A camera would read light that is reflected. Difference light conditions would give different results and hence this. Every camera comes with this setup. I am though not very sure for film cameras. 
But, white balance is something that can be changed even after you have clicked your image. So, trust me this may not be a part of exposure as some may say but relatively logical to mention here. 

Summarizing for exposure.
Shutter speed,  Aperture and ISO would control the incident light, its duration and its effect. While these three are the basic features that can control the darkness and brightness level, a camera has its own activities and hence alterations. These are metering and white balance. We will discuss these in detail later, but, the point worth mentioning here is that these are also playing their parts in exposing a subject. Hence, always keep in mind these 5 things whenever you click a snap. 

Exposure in Photography

In definition, exposure is the amount of light allowed to fall on each area unit of a photographic medium (photographic film or image sensor) during the process of taking a photograph. Exposure is measured in lux seconds, and can be computed from exposure value (EV) and scene luminance in a specified region.

A photograph is all about exposure. A properly exposed picture would ensure the details that you are trying to get out of a subject and showcase is actually visible. Also, exposure gives the dramatic effects that you would want to achieve in certain scenarios.

Now how would you achieve you desired level of exposure control. Luckily all cameras work on the same principles - the exposure triangle.

Exposure Triangle

The three features that can help you control exposure are
1. Shutter speed
2. Aperture
3. ISO

Lets discuss about these in detail. But before that I would want us all to understand, how a camera works. The basics of the camera is explained in the blog here just in case you want to dig down the details.

These three features should be present in almost all the digital cameras. Film cameras will not have ISO, instead it should have film sensitivity. 

Shutter Speed
Every camera works on this simple feature, allow light to fall on a sensitive medium and particular amount of time. In very simple terms the amount of time for which the light falls on the medium is the shutter speed. Although, this definition is only for our understanding. Mechanically speaking, a camera uses a shutter to shield light from falling on the recording medium. This shutter is released or opened when we click the camera button to take a photograph. Shutter opens for a predetermined amount of time, during which the light falls on the medium and then the shutter closes again stopping light to fall on the medium. The moment for which the shutter opens is called the shutter speed. It can range from 30 seconds to 4000th of a second(obviously this depends on the camera) or even higher. 

Aperture
Every camera works on this simple feature, allow light to fall on a sensitive medium and particular amount of time. Simply said, the amount of light that falls on the recording medium is the aperture. Mechanically putting, an aperture is the hole through which the light is allowed to fall on the recording medium. The size of this hole can be increased or decreased based on our requirements. This can range from f1.8 to f22 where 1.8 is the biggest (This depends on the lens attached). 

ISO
Every camera works on this simple feature, allow light to fall on a sensitive medium and particular amount of time. The ISO of a sensor is can be said as the sensitivity of the sensor or the recording medium, to light. As light is incident on the sensor it triggers an electronic event (for simplicity). This event is the information that is to be recorded. The information is nothing but the photographic image through light rays falling on the sensor. Now, the intensity of the event can be controlled and hence the sensitivity of medium to light. This ranges from ISO 100 to 6400 and higher(depending on the sensor). 

We can now safely assume now that at least the basics of these pillars of exposure in photography are a bit clear. I still have a question, even if I understand these basic concepts in terms of a camera, still, how is my exposure getting effected. Even before we answer this question we should understand exposure in terms of a photograph. 
There may be many articles online that explains these fundamentals. I as a beginner went through many of them to understand exposure. What many of these commonly found articles do is that they explain about these in detail. I found it very difficult to relate it to the pictures I took. It was very easy for me to understand how a shutter works and how an aperture behaves and even for you I trust these would not be an issue at all now. Try and relate these with the pics you would want to click.

Exposure is nothing but how bright or dark your image would be when it is captured. An ideal scenario is perfect exposure, neither too bright or too dark. This can be well easily said but very difficult to perform. Exposure is dependent on the light around. Night scene would mean very less light and noon would mean very bright light. Different scenes would mean different light conditions and hence exposure varies accordingly. The above three parameters would come to our rescue here. All the above three parameters would control exposure for us and give us our desired result. Remember the combination of all the above would give us a perfectly exposed picture. 

Shutter would ensure the time frame for which the light falls on the medium. The more the time for which the light falls the more the exposure. Hence, the less the shutter speed the more the exposure. For example, a shutter opening for 30 seconds is definitely more exposed than a shutter for 5 seconds. 
Aperture allows the quantity of light to fall on the medium. Hence, the wider the aperture the greater the exposure. f1.8 is far more exposed than f16.
ISO is medium's reaction to light. The more the ISO the more the exposure. Therefore an ISO 1600 would mean more exposed pic than ISO 100.
In terms of a photograph, if you want you picture to be brighter then either reduce your shutter speed or increase aperture or increase ISO. You could also work in a combination by altering any of these.

The works of these three and their play in photography will be detailed out later. For ease in understanding we should know that there are effecting the exposure in the ways we discussed here. 

Exposure would continue in the next article.

How a Camera Works

What exactly do we understand when we talk about a camera. Well, a camera can be called as a optical device used to record visual scenarios in the form of a photograph or a movie. While a camera can be said to be based on how a human eye works, but with subtle differences. 

As mentioned above, the camera should have two main parts
1. The optics - to see an image
2. Recording medium - to record the image.

Of course there are many other important mechanics involved, but not mentioning them here for the sake of brevity.

The main mechanics that we would concentrate on is that light from a distance source is allowed to fall on a medium that is sensitive to it. This is basic of any camera. 

  

The above picture shows us that we allow light rays from a distance source to travel through a container and then allowed to fall on a recording medium. Simple right? This is not that simple though. Light has to be focused on the medium to obtain clear and sharp images. This is achieved through optics. An optical part converges right rays to be focused on to the recording medium. This way we allow a more concentrated or a convergent form of light to fall on to the recording medium.

The above fundamental is simple and explains the principle of how a camera works.
In modern day camera the recording medium is a sensor that is sensitive to light rays falling on it. The Optic is a lens that throws focused light on the sensor. The film camera had light sensitive films to record images. 

Just extending the above a bit.

The above diagram shows how a camera displays what is sees to the user and then records the same. The flip mirror directs light to the view piece where the user sees what is about to be recorded. As the user presses the "Shutter" button the mirror flips and the light starts falling on the sensor. The sensor starts recording the information. 

This is a very simple depiction of the way a camera works. The idea behind is to understand the basics of a camera that will help in photography. 

Now that we understand the simple physics let us move to other aspects of the blog. Remember, this section only dealt with the understanding the basic fundamental behind how a camera should work. There are many articles on the web that describes these in detail and hence if you want to know more please dig down further into those. 
1. How stuff works
2. Wiki pedia

There are many more on the same. The idea though here was to understand the very basic of how a camera works and only the ideas that will help in photography.

There are many components that need further explanation like sensors etc. but these would be covered later on.