May 022011

Lets see the basic difference between angle of view of different tyoes of lenses.

Angle of View is what is the maximum a lens can see if set at the widest focal length. At the widest focal length you can capture maximum width of the area or Subject plane in context.

For example in the image below assuming the distance between the camera and subject is
same, see how different types of lenses provide different views of the same scene.

Angle of View

Angle of View

1. Fish Eye Lens view : A fish eye is capable of providing widest view and can produce even 180 degree view in some cases.

2. Ultra Wide Angle lens view

3. Wide Angle Lens view

4. Telephoto Lens view

5. Ultra Telephoto Lens view

Hope this simplifies understanding of different tyes of lenses.

Feb 242011

You must have heard of the term “stop” or “stop of light”.  Lets understand what is this and how it affects exposure. we will also see how stop is used to express exposure values.

What is It?
“stop” can be considered as unit of light entering into the camera. In simple terms if we say 1 bulb gives 1 stop of light so 2 bulbs will be 2 stop of light

Stop of Light

so 2 bulbs is 1 stop more than 1 bulb.

How to Calculate it
The focal length of a lens is the distance between the optical center of the lens and the camera sensor. The longer the focal length, the more it “magnifies” the subject.

f-stops are a measure of the aperture of a lens. In other words, f-stops tell us how wide lens opens. Its the ratio of focal length to apparent lens aperture. The smaller the number, the wider the effective aperture, and the more light will go through the lens. Hence f1.0 is a wide aperture, but f8.0 is a narrow aperture. You can read more on Aperture here.

If we have to calculate the amount of light entering in the lens, we should consider the Area of aperture as amount of light will be proportional to the area. Here is the formula to calculate the area:

Area Formula

f  :  Focal length
N  : F-Number

Assuming the Focal length remains same for our comparison. Lets say 50 mm. Here is how the area of aperture will be for different values of F-Number

Area of aperture

Notice that increasing the Aperture (F-Number) from 2.8 to 2 increases the area by double which mean double the light and hence we can say that f/2 is 1 stop more than f/2.8 or in other words f/2.8 is one stop less than f/2. Now since the amount of light exposed to sensor is also dependent on other factors such as ISO, Shutter speed so term “stop” is used in their context as well.

Lets say we change our shutter speed from 1/1000 sec to 1/500 sec thus increasing the shutter time by twice and hence double the light will be exposed to sensor. We can therefore say that 1/500 is 1 stop more than 1/1000 assuming all other settings are same.

Similary, ISO is sensitiveness of camera sensor and is expressed as standard values of 100, 200, 400, 800, 1600 etc. As the ISO number is increased sensitivity of sensor increases and thus less light is optimum for exposure. So we can say that ISO 200 is 1 stop more than ISO 100 and so on…

Here are few more examples to express what we have learnt so far:

f/8 is 1 stop less than f/5.6
ISO 800 is 1 stop more than ISO 1600
1/125 is 2 stop more than 1/500

In Camera Representation
Here is how most of the cameras show builtin meter for showing exposure value

Camera Meter

Center one is optimum exposure
On the left (-) end less exposure values are shown
On the right (+) end more exposure values are shown

The scale is shown with “stop” as a unit. See that on each side 3 units of stop are shown with small lines showing partial stop values. So if you adjust your camera settings like ISO, aperture, shutter speed etc. and the “pointer” is at right side at the “1″ so you can say that you are exposing 1 stop more than optimim exposure.

Stop down & Stop up
These terms are used in photographic communications often. Stop down means reducing the stop value and hence less light and hence under-exposing whereas Stope up means increasing the stop value and hence light and over-exposing.

If I say that “I need to stop down my aperture by 1 stop from f/4″ . It means…  I have to change the aperture value from f/4 to f/5.6 as it will decrease the light by 1 stop.

I hope you understood by now and can relate the stop of light when used in photographic discussions or in your daily use.

Hope it helps! In case you like to share your views on this please leave your comments below…

Feb 082011

While taking a photograpgh one needs to take care about the right amount of light to which camera sensor is exposed so that the shot is created as desired. It is called exposure. There can be multiple correct exposures for a single photograph.The correct exposure is the one photographer decides in order to depict what he wants in the photograpgh. 

Exposure is affected primarily by 3 different aspects of photography. These are Aperture, Shutter speed and ISO as shown in the diagram below. 

Exposure diagram

Exposure diagram


Lets define these properties and understand what they are and how they affect each other which deciding on thr right exposure. 

Aperture  is defined as size of opening of diaphragm or in other words its the amount of light passed through the lens and is expressed in terms of F-stop values e.g. f/1.8, f/4, f/5.8 etc. Higher the value of f/number bigger will be the size of light. 

Shutter speed is the time period the shutter remains open and thus its the time period for which the light is allowed to pass through the lens. Shutter speed is expressed in terms of  seconds or fraction of seconds e.g. 2″, 1″, 1/2, 1/8, 1/16, 1/1000 etc. Needless to say that 2″ is longer than 1/2. 

ISO is the standard for sensitiveness of camera sensor to light. How sensitive is camera sensor to light and is expressed as standard values e.g. 100, 200, 400, 800 etc. ISO 100 being least sensitive and ISO 200 being 2 times more sensitive than ISO 100. 

Lets see how these 3 work together. 

Assuming that we have set our ISO to 100 and we need aperture to be f/4. On camera meter, for proper exposure we get the shutter speed to be 1/1000 sec. This means that these settings f/4 @ 1/1000 for ISO 100 gives us the correct exposure as per our in camera meter. This is one set of exposure settings. 

f/4 1/1000 @ ISO 100   = correct exposure 

Now lets change the aperture to f/5.8 which is one stop less than f/4 it means that we are allowing almost half of the light and hence in order to get the correct exposure for teh same shot we need to increase the time period of light and thus Shutter speed should be 1/500 instead of 1/1000 

f/5.8 1/500 @ ISO 100   = correct exposure 

Now lets change the ISO to 200 instead of 100 which means that our camera sensor is now 2 times more sensitive to light so we can have sensor exposed for shorter duration and thus it can live with half of the shutter speed. Thus in order to get the same exposure we need to have the following values 

f/5.8 1/1000 @ ISO 200   = correct exposure 

Above example shows how these three values ISO, Shutter speed and Aperture are inter related and affect exposure. 

Follwoing table shows some other settings of exposure values which all provides the same result for the same shot 

Exposure table

Exposure table

and many more …. 

If all of the above settings are same so how do we decide which setting is more appropriate for our shot. The answer to that lies in the fact what aspect of the photograpgh is affected by these 3 values. 

As this is already a big post Lets keep it that to the Next part of this series.
(will update the link here soon)

Feb 042011

Think of Aperture as a measure of the size of opening of the lens. Its basically the diaphragm  size.

When you look at the lens from back after removing it from the camera body there is a lever that you can move to see the diaphragm in action. It opens or closes with that lever. Its the diaphragm that affects the size of light coming in through the lens. So the bigger the size of diaphragm more will be the light coming to lens and hence to camera sensor.

Bigger Diaphragm opening = More light through lens

So Aperture is a measure of size of opening of diaphragm. Bigger diaphragm opening means Large aperture and smaller opening means Small aperture.

 Bigger Diaphragm Opening = Large Aperture = More Light
 Smaller Diaphragm Opening = Small Aperture = Less Light

So now we know that Aperture affects amount of light entering and thus would affect overall exposure of the shot.

Aperture is denoted by “A” or “Av” mode on most of the SLR cameras. This mode lets you change aperture setting and rest of the exposure settings are controlled by the camera itself to provide the right expousure.

Now, Aperture value is expressed as “f-stop” value and is usually the following standard values:

F-Stop : f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16

Notice the representation of f-stop value as f/N
The lower the number (N) Larger will be the aperture and similarly higher the N number smaller will be the aperture.

So f/2 is much larger aperture than f/16. It means that f/2 will allow more light to enter in lens as compared to f/16 and thus we can use a faster shutter speed to get the same exposure.

What is a “Stop” in the above ? A stop is a unit of light. All the values expressed above are 1 Stop more or less than each other. In other words f/2 is 1 stop more than f/2.8 and f/11 is 1 stop less than f/16.

Aperture affects “Depth of Field” in the shot. The larger the aperture (means smaller Nnmber) shallower will be the depth of field.
I will be covering depth of field in a separate post.