Aperture

Aperture Values...

I will start off by trying to keep this simple, I may however proceed to ramble on about the technicalities and mathematics of it all at a later date...

The aperture values in relation to the actual f-stop number can be confusing to the beginner as the larger the f-stop number the smaller the actual aperture becomes... I have found the easiest way to convey this is to treat the f-stop numbers as fractions, f/1 being the maximum or whole aperture and all the other f-stops are fractions of that whole f-stop... We all know that a 1/4 is smaller than a 1/2 so f/4 is a smaller aperture than f/2 so on and so forth... Each time the amount of light allowed in is halved starting from a maximum aperture of f/1 it is given a full f-stop number, the full f-stop numbers are f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64 and f/90... These numbers may seem to have funny values as this is due to the mathematical equations when calculating the area of a circle, sorry I said I would keep it simple so back to the basics... Your lenses will not have all these f-stops available to them but your camera or lens may allow you to use increments in 1/3 or 1/2 stops... Below are two examples of these increments...

An aperture value of f/1.8 is 1/3 of a stop faster than f/2 (allows in 1/3 of a stop more light than f/2) but 2/3 of a stop slower than f/1.4 (allows in 2/3 of a stop less light than f/1.4)
An aperture value of f/6.7 allows in 1/2 a stop more light than f/8 but 1/2 a stop less light than f/5.6...
Basically an aperture is the size of the hole left by the diaphragm blades of a lens when it closes down... This hole allows a certain amount of available light to pass through to the film or digital sensor when the camera’s shutter opens...

Below you will see two 50 mm Canon EF lenses, the one on the left is a f/1.4 and the one on the right is a f/1.8... You will notice that the size of the maximum available aperture is much greater on the f/1.4 than it is on the f/1.8 even though this only represents 2/3 of a stop in value... The Canon EF f/1.8 lens has a diameter of 68.2 mm, the f/1.4 has a diameter of 73.8 mm the f/1 (not shown) has a diameter of 91.5 mm, the larger diameters are to allow for the larger apertures required in making faster lenses...

We now know three things about apertures...

1... That an aperture is a hole left in the lens by the diaphragm blades when they close down, controlling the amount of light allowed in...

2... That each size of aperture is given an f-stop number...

3... That the larger the f-stop number the smaller the aperture...

There are a few other questions you might want answers to...

1... What are the advantages of having a wide aperture lens/fast lens?...

2... What effect will a large aperture produce?...

3... What effect will a small aperture produce?...

Here are some of the answers...

1... The wider the maximum aperture the lens has the easier the lens is to focus in low light because the lens focuses at maximum aperture and only stops down to the selected aperture a fraction of second before the image is taken...

2... Wider apertures allow faster shutter speeds in low light conditions allowing you to minimise, or prevent blur in moving objects...

3... Large apertures like f/2.8 will produce a shallow depth of field (DOF) which means a very limited distance from the point of focus of the image will be of acceptable sharpness... Large apertures are often used in portraiture to separate the subject from the background... They can also be used to concentrate the eye to a certain part of an image, this technique is called selective focusing (See below)... Small apertures (large f-stop numbers) give greater DOF allowing more of the subject from front to back to be of acceptable sharpness... Large apertures are often used in landscapes and macro work to keep as much of the image as sharp as possible...

Selective Focusing...

With this cropped image of a squirrel I decided that the important things in the image were the squirrels face and the hands holding the peanut... I used a Canon 10D with an EF 200 mm f/2.8L lens opened up to its maximum aperture to try and isolate these two parts of the squirrel from the rest of the image by keeping them sharp and blurring the rest... The wide f/2.8 aperture allowed me to do this by limiting the DOF to make them stand out... If I had used an aperture of f/4 or smaller the selective focus and the effect would have been lost...

Well hopefully that’s the basic information on apertures explained... If you have read my page on shutter speeds all that you need to do now is combine the correct aperture with the correct shutter speed to create your masterpieces, remembering when to compensate for tricky lighting situations ...

	Freelance Photographer Seeing things differently A taker of Photographs - A creator of images
Kennymc.com


Aperture Values... I will start off by trying to keep this simple, I may however proceed to ramble on about the technicalities and mathematics of it all at a later date... The aperture values in relation to the actual f-stop number can be confusing to the beginner as the larger the f-stop number the smaller the actual aperture becomes... I have found the easiest way to convey this is to treat the f-stop numbers as fractions, f/1 being the maximum or whole aperture and all the other f-stops are fractions of that whole f-stop... We all know that a 1/4 is smaller than a 1/2 so f/4 is a smaller aperture than f/2 so on and so forth... Each time the amount of light allowed in is halved starting from a maximum aperture of f/1 it is given a full f-stop number, the full f-stop numbers are f/1, f/1.4, f/2, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, f/32, f/45, f/64 and f/90... These numbers may seem to have funny values as this is due to the mathematical equations when calculating the area of a circle, sorry I said I would keep it simple so back to the basics... Your lenses will not have all these f-stops available to them but your camera or lens may allow you to use increments in 1/3 or 1/2 stops... Below are two examples of these increments... An aperture value of f/1.8 is 1/3 of a stop faster than f/2 (allows in 1/3 of a stop more light than f/2) but 2/3 of a stop slower than f/1.4 (allows in 2/3 of a stop less light than f/1.4) An aperture value of f/6.7 allows in 1/2 a stop more light than f/8 but 1/2 a stop less light than f/5.6... Basically an aperture is the size of the hole left by the diaphragm blades of a lens when it closes down... This hole allows a certain amount of available light to pass through to the film or digital sensor when the camera’s shutter opens... Below you will see two 50 mm Canon EF lenses, the one on the left is a f/1.4 and the one on the right is a f/1.8... You will notice that the size of the maximum available aperture is much greater on the f/1.4 than it is on the f/1.8 even though this only represents 2/3 of a stop in value... The Canon EF f/1.8 lens has a diameter of 68.2 mm, the f/1.4 has a diameter of 73.8 mm the f/1 (not shown) has a diameter of 91.5 mm, the larger diameters are to allow for the larger apertures required in making faster lenses... We now know three things about apertures... 1... That an aperture is a hole left in the lens by the diaphragm blades when they close down, controlling the amount of light allowed in... 2... That each size of aperture is given an f-stop number... 3... That the larger the f-stop number the smaller the aperture... There are a few other questions you might want answers to... 1... What are the advantages of having a wide aperture lens/fast lens?... 2... What effect will a large aperture produce?... 3... What effect will a small aperture produce?... Here are some of the answers... 1... The wider the maximum aperture the lens has the easier the lens is to focus in low light because the lens focuses at maximum aperture and only stops down to the selected aperture a fraction of second before the image is taken... 2... Wider apertures allow faster shutter speeds in low light conditions allowing you to minimise, or prevent blur in moving objects... 3... Large apertures like f/2.8 will produce a shallow depth of field (DOF) which means a very limited distance from the point of focus of the image will be of acceptable sharpness... Large apertures are often used in portraiture to separate the subject from the background... They can also be used to concentrate the eye to a certain part of an image, this technique is called selective focusing (See below)... Small apertures (large f-stop numbers) give greater DOF allowing more of the subject from front to back to be of acceptable sharpness... Large apertures are often used in landscapes and macro work to keep as much of the image as sharp as possible... Selective Focusing... With this cropped image of a squirrel I decided that the important things in the image were the squirrels face and the hands holding the peanut... I used a Canon 10D with an EF 200 mm f/2.8L lens opened up to its maximum aperture to try and isolate these two parts of the squirrel from the rest of the image by keeping them sharp and blurring the rest... The wide f/2.8 aperture allowed me to do this by limiting the DOF to make them stand out... If I had used an aperture of f/4 or smaller the selective focus and the effect would have been lost... Well hopefully that’s the basic information on apertures explained... If you have read my page on shutter speeds all that you need to do now is combine the correct aperture with the correct shutter speed to create your masterpieces, remembering when to compensate for tricky lighting situations ...

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