Camera for Dummies: Aperture

Hope you had a look at the artical on basics of camera.

Unit of the size of an apaperture is f-stop. An f-stop indicates the size of the aperture with respect to the [effective] focal length of the lens [attached to the aperture]. Physical size of the aperture (i.e. the diameter) is reciprocal to the f-stop of the aperture. Meaning the bigger the f-stop, the smaller the physical size of aperture. See figure below.

Note: Why use some creepy thing like f-stop when you can represent the same thing using a simple unit like milimeters [for diameter]? Well, using f-stop makes the unit independent of the focal length of the lens, so when you say that there are 2 lenses [having different focal length] with aperture = f/2 you know that both of them allow same amount of light to pass through. But if you say that there are 2 lenses [having different focal length] with aperture = 12 mm, both will NOT allow same amount of light to pass through.

Like we have the decimal series 0, 1, 2, 3 and so on, we also have an "f-stop series" which goes like this: f/1.4, f/2, f/2.8, f/4... If you are a math genius you would've figured out formula of the series. But if you also didn't score high in math like me here is how it works. The denominators are simple multiples of 1.4142135623730950488016887242097. Why this strange number? Well it is root-2 (square root of 2). And when you multiply denominators with root-2 the aperture size/area decreases in such a way that it allows half the light to pass through. E.g. if an aperture of f/1.4 allows X amount of light to pass through it then [f/(1.4*1.4)=] f/2 will allow X/2 amount of light to pass through it and f/2.8 will allow X/4. Hope now you understand the figure above. :).
Refer to: Wikipedia: F-stop for details. 

Now lets look at the side-effects of different aperture size. This is where the optics comes in.

If the aperture is big we will have deeper depth-of-field or DOF. What is DOF you'll ask? Technical definition of DOF is the distance (perpendicular to the camera) in which the subjects have a clear focus.

Photo below gives you an idea. As you can guess the left most was taken using big aperture (say f/1.4), where as the right most was taken using a smaller aperture (say f/22). Refer to Wikipedia: DOF. Difference can be seen clearly when you see how well the columns far from camera are in/out-of focus.

So why would I want to blur a photo using big aperture when I can get a nice and clear picture using smaller aperture? There are 2 straight-forward cases when one will need to use a big aperture:
1. When you are taking portraits: (Portrait photography is a style of photography). Photo below (courtesy photo.net) is a bright example of a portrait. This photo is taken with a big aperture. Imagine if the you were to see all other details (e.g. the building in the back- ground and the street light) would the photo have same impact? So usually a portrait photographer uses a lens that supports a big aperture (f/2, f/1.4, f/1.2..)
2. When the ambient light is low e.g. in late evening. As we learned earlier if the brightness of light is less AND the camera's shutter speed can not be slowed down below a limit (so that the light is allowed to expose the film for a longer time) then one is forced to use a big aperture so as to keep shutter speed at an acceptable value. Refer to shutter related section for some more info.

Now we know when to use a big aperture. So it's implicit when to use a small aperture ! When taking pics of landscapes (gardens, mountains, rivers city block/street) or architecture (castles, buildings, towers) one would want to capture details and not only a part of what is seen so these are the situations where you close down your lens to say f/8 or less (less means f/11, f/16..).

See the landscape photo below for example. Everything near, far and in between adds to the picture, we wouldn't want any of the boats or the clouds (which are far away) out of focus.

A bit more of jargon about lenses. Camera lenses' specification would provide the biggest aperture size that the lens can handle e.g. "Canon EF 50mm, f/1.4". It means the lens' focal length is 50mm and largest aperture it can handle is f/1.4. The lower limit (smallest aperture supported) is usually not of interest as most lenses support small enough aperture to take care of most photographic needs. When a photo is taken at the biggest supported aperture of a lens it's called "lens was kept wide open", the opposite of that would be "lens was closed down".
Finally, lenses with bigger max aperture cost more than those with smaller max-aperture, e.g. Canon EF 50 f/1.2 costs $1500 whereas Canon EF 50 f/1.8 ii costs $110!!

For zoom lenses f-stop spec is usually provided at both ends of zoom range, e.g. Canon EF 28-105 f/3.5-4.5, means when lens is set to 28mm, max aperture is f/3.5 and when lens is zoomed to 105mm the max aperture is f/4.5, min aperture in both cases would be quite small like f/16-18. Lens with a fixed focal length (e.g. the 50mm above) is known as a prime lens.

To summerize:

• Bigger the aperture (smaller the f-number) shallower the DOF. Useful in low light conditions as well as portrait photography.
• Smaller the aperture (bigger the f-number)  deeper the DOF. Useful in landscape, architecture and other forms of photography where details of most things in frame are expected to be clear/in-focus.

That concludes the aperture story. Lets move on to shutter speed.

Camera for Dummies: Basics

Camera:A boxlike device for holding a film or plate sensitive to light, having an aperture controlled by a shutter that, when opened, admits light enabling an object to be focused, usually by means of a lens, on the film or plate, thereby producing a photographic image.
That's what a Camera is according to Dictionary.com. But believe me it's much simpler than that. :)

To understand the how a camera works lets see how the oldest cameras were designed. The oldest type of cameras were the pin-hole cameras.
Lets create a pinhole camera:
1. Take a sheet of paper and make a hole in it. Diameter can be around 0.5-1 mm not more.
2. Select a wall on which the light is coming almost perpendicularly.

3. Now you need to find out "the distance". This is the distance between wall and the camera (i.e. the sheet of paper) that will expose/create the image on the wall. To to this hold your camera about 1 cm away from the wall and move it away from the wall till you see the picture on the wall.
When you see the image, you have your camera !

Of course you'll say where is the photo ?! Well, it's on the wall, if you want to make it permanent you need a wall that can capture it. Now no one has discovered a wall like this so far but once up on a time someone put some silver dust on surface of something. Knowingly or unknowingly he managed to let some light on this surface. It turned out that the image represented by that light was imprinted on it. Thus was invented silver screen. After lotsa ppl put lotsa thought into this invention, today we have the "camera film".
So to complete our pinhole camera all we gotta do is replace the wall with this film !

Of course you have to ensure that no other light other than the one from your pinhole reaches this film coz then image will be distored.
So what do we do? Instead of just using a single sheet of paper we use a box. With a hole in one side of it and the film on the opposite side. All other sides are covered so the light come only from the hole onto the film, thus capturing the image we want and not something else. So do we have our camera now ??

Not just yet, there still the question how long do I have to expose the film to the light? We know the films are sensitive to the light, Unfortunately if you expose them to little light for a long time, it'll still have the same effect as exposing lots of light for a short duration. So what do we do ? Well, we put some mechanism to control how long the film is exposed to the light.

For the purpose of this explanation we'll use a very crude mechanism to control the exposure time. Take a sheet of paper and cover the hole with it so no light passes through. Now lets say we know that given the amount of light around we need to expose the film for one full second (in practice it's MUCH lesser time), so put the film on the opposite wall of the hole, remove the sheet of paper covering the hole and put it back after one second. Your own little camera is ready.

Now lets look back at what we've done and get introduced to some technical jargon.

• First we created hole in one wall of the box: This is your lens. In practice you'll use an optical lens made of glass.
• Say the diameter of our hole is about 1mm: This is your aperture. In practice the aperture is measured in terms of f-stop instead of mm.
• Then we put a film on the opposite wall: This your film. :)
• We also ensured that the distance between our lens and the film is such that the image is clear (technical term is "image/subject is in focus"): This distance is the focal length of your lens.
• We used a sheet of paper to control the exposure time: This is your shutter.
• Using this shutter we allowed the light to pass through the aperture/lens for 1 second: This is your shutter speed. The longer we allow the light to pass the faster the shutter speed and vise-versa.

The basic principle-of/thing-about photography is to control the amount of light you allow to reach the film. This will ensure that you see the image on the film. Technically this is called controlling the exposure. If you let less than required amount of light to pass the photo will be under-exposed. There are 2 basic ways of controlling exposure:
1. The aperture size: Diameter of the hole through which the light passes.
2. The shutter speed: Duration for which the shutter is kept open to allow the light to pass through the aperture.
In the next artical on aperture we look what can one do with aperture and what will be the side-effects.