still confused by F-stops

Mattw

Mattw

Mattw

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Joined
15 May 2006
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Hi,

im now starting to understand a bit more of the technicalitys behind photography. However im still very confused by F-stops. For example a lense is 4-5.6 what does those figures actually mean?

Then you can change it on the camera from like 4-22 or whatever, but those numbers are different to the lense? why?

Maybe someone has a visual explanation what might help me understand, i have read a couple of different answers to this question and am still left non the wiser.
 
The Fstop number listed on a lens represents the diameter of the maximum aperture. Say 4.5 ( this is the maximum aperture this lens can achieve and this is also referred to as "Wide open")

aperture.gif


The numbers listed on lenses such as F4.5 F4 F2.8 F1.2 means that the aperture diameter is going to be much wider meaning the lens will be constructed with physically more glass inside adding drastic cost productions and weight

image007.jpg


The wider the aperture is (number closest to zero) the more bokeh you will achieve in your photographs. This is also referred to as shallow depth of field.

To change your aperture from a wide aperture number to a range such as F8 F11 F16 F22 then this is whats known as closing down your aperture which will make the diameter of the aperture very small and allow less light to pass which also gives you a greater depth of field meaning that more of your frame will be in focus (F22 is mainly used for landscape work where your foreground and background portions are all required to be sharp focus)

Hope this is somewhat more clear to you now.
 
Mattw said:
However what is aperature :)
Click to expand...
It's the size of the physical opening in the lens.

Imagine a lens to be a window and completely ignore the fact that a lens is circular and our window is square. On this window is a blind and there's the sun shining through the window, illuminating the room that the window is in.

Now, if you have the blind slightly open you get a small amount of light in and the room remains quite dark. If you open the blind completely the light pours in and the room is very bright. The aperture is the amount of window that the blind isn't covering - a large aperture (which is a lower f/number) lets in a lot of light, a small aperture (a higher f/number - notice the inverse relationship) lets in a little light.

You can also explain aperture by means of a water pipe (lens) and water (light). A water pipe with a large aperture (low f/number) will let a lot of water flow through it. A pipe with a small aperture (higher f/number) won't let as much water flow.

This example is easier when you come to explain the effect of shutter speed and aperture on exposure, but that's for another time perhaps.
 
also when a zoom lens states a maximum of F4-5.6 then it is telling you that the aperture will be F4 at its widest angle and 5.6 at the longest angle , this seems to be more common on budget lenses as pro lenses tend to have a single maximum aperture
 
JBuk said:
also when a zoom lens states a maximum of F4-5.6 then it is telling you that the aperture will be F4 at its widest angle and 5.6 at the longest angle , this seems to be more common on budget lenses as pro lenses tend to have a single maximum aperture
Click to expand...
Yes, otherwise known as a aperture across the range. such as F4
 
yep, the max it will open is to 4. Which means in low light situations you won't have the benefit of being able to open up the lens more to let more light in. This means you will have to either up the ISO (noisy images) or leave the shutter open longer (to allow more light in for proper exposure) but that means if anything is moving it will get blurred.
 
Now having learned that you should be able to compare and use them with exposure times.

Originally a very long time ago camera used to only come with the standard F-stops F1.4 F2.8 F5.6 F11 F22 each being half the diameter of the last in the standard F-stop range and lets in half the light.
However this can still be applied now, say your camera meters a shot on F8 @ 1/60th of a second you would get this.

F2.8 - F4 - F5.6 - F8 - F11 - F16
1/500 1/250 1/125 1/60 1/30 1/15
Each one of these is the correct exposure for the applied F-stop based on knowing that F8 will expose correctly at 1/60 (your camera or a light meter will tell you this)

You can use this if you want to apply artistic depth of field.
You might for instance do this.
Camera meters in automatic for F11 for 1/30th of a second.
Using that scale you want low depth of field you would put the aperture to F4, thus dropping three stops, so...

F4 - F5.6 - F8 - F11
1/250 1/125 1/60 1/30
As the size of the aperture grows, i.e F4, depth of field reduces, and incoming light increases, thus meaning you need less time for a correct exposure.
 
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