Aperture in photography: What is f/stop and the relation with aperture

Very often if not always, in photography you will see, if not already seen, those fraction numbers which look like: f/1.4, f/2.8, f/4 or those kind of aperture numbers f/5.6-6.3.

 

On the lenses it is printed in this way 1:4 or 1:5.6-6.3 to designate the maximum opened aperture. And more rarely this way too f:5.6-6.3 (f:x instead of f/x where "x" represent a number) i gave you this one also in case you encounter it ... one day ... you will not be surprised.

 

At first to eliminate any confusion, you need to know that 1:4 mean f/4. Yes, they mean exactly the same thing! Let's try another one 1:3.5-5.6 mean exactly f/3.5-5.6 or f:3.5-5.6 all the same ... exactly the same meaning!

 

So what is the meaning of those strange numbers and their relation with the aperture ? But most important, what's the meaning of Aperture in photography?

 

Those strange numbers like f/4 are the ratio (fraction-scale) of the size of the iris aperture which give, control and tell you the amount of light you are controlling to hit the sensor of your camera.

Aperture of a lens with a simple explanation

To make it simple, let's compare the aperture to a valve or a water hose: More the diameter of a hose is wide more water can run thru it, more you open the valve more water can get out of the faucet.

Aperture in photography is the same thing, but the faucet or the hose is called iris diaphragm in photography and it is this iris diaphragm that you control how wide or narrow you want it, to let pass the light to hit the sensor.


Example of different aperture on the iris diaphragm of a lens
Example of different aperture on the iris diaphragm of a lens

On the side and just are two pictures of the diaphragm of one of my lenses (the sigma 85mm f/1.4) at two different apertures.

The first picture show an aperture of f/3.5 and the second an aperture of f/7.1 or f/8 (i don't recall),  and you can see that the diaphragm at f/3.5 is a lot more wider than at f/7.1.

 

So, what does mean this f/x fraction number? and how to get them, but more important what's their exact meaning like f/7.1 and f/3.5 or f/11?


Below the best video i found on youtube (from Dylan Bennett) to really understand the f-stop scale with a very simple explanation about f-stop (you will not loose your time, believe me!)

So now that you understand what's aperture and f/stop (if you have watched the video above), i will give you some tips about when and where to use a wide aperture like f/2 or a narrow aperture like f/8 or f/11.

 

Wide aperture are good for portrait photography or low light situation, narrow aperture like f/11 or f/16 are often use for landscape (with a tripod) or when we want a big depth of field (soon "what's depth of field?") or a slow shutter speed without filters.

 

You might have heard or read about those two words "fast lens", so a fast lens is a lens which can open very wide, usually a lens who can open to f/2.8 is considered to be fast by the majority not only because it let pass a lot more light than f/4, in fact it let pass the double amount of light than a lens which can open at it's widest at f/4, but at f/2.8 the glass of the front element of a lens start to be quite big.

 

What's the widest aperture on a lens which are considered fast, i would say it depend also bout the focal length, but let's give a between:

All wide angle at f/2.8 and wider aperture like f/2 are considered fast lenses.

50 to 100mm f/2.8 to f/1.4 is fast to very-very fast.

101 to 200mm f/2.8 to f/2 is fast to very-very fast.

201mm to 400mm f/4 is fast, if f/2.8 it's very-very fast.

401mm to 600mm f/5.6 is fast, if f/4 it's very-very fast.

 

Fast lens are usually more expensive than average lens, but if you are shooting people at night or indoor, you will often need a fast lens to not blur people with a slow shutter speed due to the lack of ambient light.

 

Aperture and it's f/number have also an effect on what it's called : The Depth of Field, and this effect is one of the most important effect in photography.


 You might also be interested with the last entry in the blog:

Photophone: How to do great pictures with a smartphone or a tablet.

How to take great pictures with a smartphone
How to take great pictures with a smartphone?

Nowadays our smartphones have more computer power than a 10 years old desktop computer. Technology is evolving fast and with it, the language acquiring new words like  smartphone or selfie.

We are doing everything with our phone, from a GPS assistant to photograph or record a movie in full 1080p HD, even post processing those images, and i don't even speak about playing 3D games, read some news on internet and so on...

 

At the end, when we compare how we use our phone the most, in percentage, I can say safely that we barely use it to call someone, and this is why i call mine a photophone.

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