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<div class="panel-heading">'''Just the Basics'''</div>
<div class="panel-heading">'''Just the Basics'''</div>
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The more open your lens (the <code>number</code> in f/<code>number</code> is lower), the more light comes in to your camera. So <kbd>f/2.8</kbd> is ''faster'' than <kbd>f/5.6</kbd>, we also discuss this trade-off under [[ISO]]. But there is more to the story.  
The more open your lens is, the more light comes in to your camera. Aperture is specified using f/<code>number</code>, where a smaller <code>number</code> means more opening. So <kbd>f/2.8</kbd> is ''faster'' than <kbd>f/5.6</kbd>, we also discuss this trade-off under [[ISO]]. At least in theory, the fastest lens setting is the best. It allows more light, so you can either use a faster [[exposure time]] helping you to capture faster moving things, compensate for movement of the camera while taking a picture (that helps with [[sharpness]] or allow you to use a less noisy [[ISO]] setting.  
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<div class="panel-heading">'''But there is more to the story'''</div>
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Practically all lenses allow you to control the ''aperture'', it is one of the basic settings. There is the maximum you can open the lens, this is the f/<code>number</code> that the lens is known with.  
Practically all lenses allow you to control the ''aperture'', it is one of the basic settings. There is the maximum you can open the lens, this is the f/<code>number</code> that the lens is known with.  


At least in theory, the fastest lens setting is the best. It allows more light, so you can either use a faster [[exposure time]] helping you to capture faster moving things, compensate for movement of the camera while taking a picture (that helps with [[sharpness]] or allow you to use a less noisy [[ISO]] setting.
So why would you want to control the aperture:
 
* Controlling the [[depth of field]], An open lens collects a lot of light at the distance it is focused on and an area just around this point. The picture is [[sharpness|sharp]] where it is focused, but blurred everywhere else. This can be used to ''tell'' the viewer where to look at, it can be a very powerful artistic tool.
But in a lot of cases you want to play with this setting. Here is why:
* Lenses are not at their best performance when fully open. The basic problem of a wide open lens is [[falloff]], that the corners of your image do not get the same amount of light as the center part of the image. Stepping up, or closing the aperture will usually help in this case. Most [[lenses]] are also a bit [[sharper]] with smaller apertures, before [[diffraction]] kicks in, and makes the image softer again.
 
* And sometimes, there is just too much light. Lenses that are open collect a lot of light, and sometimes they would need a [[exposure time]] that is shorter than your camera can manage. There are also cases (waterfalls, propellers) where you may want a specific [[exposure time]], where adjusting the aperture could help.  
=== Controlling [[depth of field]] ===
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The first problem you have is [[depth of field]]. An open lens collects a lot of light at the distance it is focused on and an area just around this point. If you collect a lot of light (when your lens is wide open) all this light comes from an even narrower distance behind and in front of where you have focused. Everything else stays out of focus and appears blurred. Do you want to have things that are not at the same focal plane appear sharp and in focus, you will need to increase the <code>number</code> in f/<code>number</code>, close your lens. So if your loved ones are posing in front of the Pyramids you have three choices
* Use <kbd>f/2.8</kbd> and have your loved ones in focus
* Use <kbd>f/2.8</kbd> and the Pyramids in focus
* Use <kbd>f/32</kbd> and have a picture where your loved ones and the Pyramids manage to appear on the picture.
 
There is actually a fourth choice. The [[depth of field]] varies with distance, so if you manage to frame your loved ones quite far (i.e. 10m) then at that distance even for a small f number you will be getting everything in focus. This is what long lenses are able to do for you. On the other extreme, in [[macro]] photography where you focus really close, the [[depth of field]] becomes a real issue.  
 
=== Lenses have issues at open settings ===
 
A completely different problem is that at its maximum settings, the lenses usually suffer more from various unidealities. The basic problem of a wide open lens is [[fall off]], that the corners of your image do not get the same amount of light as the center part of the image. Stepping up, or closing the aperture will usually help in this case.  
 
=== Too much light ===
And sometimes, there is just too much light. A rule of thumb (The Sunny f/16 rule) says:
: ''On a sunny day, with <kbd>ISO 100</kbd>, you [[expose]] at <kbd>1/100s</kbd> with aperture <kbd>f/16</kbd>'' 
Well that translates to about <kbd>ISO 100</kbd>, <kbd>1/8000s</kbd> with aperture <kbd>f/1.8</kbd>, which is faster than some cameras are able to [[expose]]. The higher the f-number, the longer you have to expose, which is what you sometimes want, either because the camera can not expose for such a short amount of time, or you want to smooth something (waterfalls, propellers) by exposing deliberately longer, and the fast lens settings will work against you. 
 
Of course there are other remedies for this, for example adding a dark filter in front of your camera to artificially reduce the amount of light coming into your lens.  
 
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<div class="panel-heading"><strong></strong></div>
<div class="panel-heading"><strong>Extreme example</strong></div>
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This shot (see more below) shows the effect of [[aperture]] on the [[depth of field]]. This is an extreme example taken by the [[Nikon 105]] [[macro]] [[lens]], which can get very close, the focus in this picture is about 40cm away from the sensor. This exaggerates the effect.
[[File:chip_f3.5.jpg|class=img-responsive]]
This is the most wide open setting for this [[lens]] at this distance <kbd>f/3.5</kbd>, the [[exposure time]] is <kbd>1/20s</kbd>. Notice that only a very narrow part of the picture is in [[focus]].
 
[[File:chip_f40.jpg|class=img-responsive]]
This is the most wide open setting for this [[lens]] at this distance <kbd>f/40</kbd>, the [[exposure time]] is <kbd>5s</kbd>, 100 times more than the previous one. Most of the frame is now in [[focus]], but we needed 100 times longer to capture the picture.
 


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=== More example pictures ===
You will see the interplay between the aperture and [[depth of field]]. Just look at the right hand side for the distance markers on the green ruler (they are in mm scale), to see what is in [[focus]].


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{{Carousel5|f|File:chip_f3.5.jpg|f/3.5, 1/20s|File:chip_f5.6.jpg|f/5.6, 1/10s|File:chip_f11.jpg|f/11, 2/5s|File:chip_f22.jpg|f/22, 1.6s|File:chip_f40.jpg|f/40, 5s}}
 
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<div class="panel-heading"><strong>The speed of a lens is overrated</strong></div>
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Fact is that most modern cameras can produce excellent images with higher [[ISO]] levels, more so if you need to [[scale]] due to the limitations of the [[medium]] you are using. You can effectively speed up your system by simply increasing <kbd>ISO</kbd>. If you stay within reasonable levels, you will not even notice, unless you are counting pixels and zooming in like crazy.
 
This additional speed can be used in two ways:
* Compensate for slower lenses that have higher maximum aperture but are much cheaper.
* Increase the [[exposure time]] so that movement (both you and your subject) effects the [[sharpness]] of your picture less. 
<br>
The [[obsession with fast lenses]] dates back to a time, where photographers were limited by the film they used in their camera. You can simply move from <kbd>ISO 100</kbd> to <kbd>ISO 400</kbd> to compensate the speed difference between a <kbd>f/1.4</kbd> and a <kbd>f/2.8</kbd> lens. 
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{{Photodisclaimer}}
{{Photodisclaimer}}

Latest revision as of 14:58, 31 December 2020

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Letting light into your camera

Aperture literally tells you how much the opening is in your lens that lets light into your camera. But that is not the entire story, you balance the amount of light coming into your camera which effects speed (and exposure time) with depth of field. Sometimes deliberately.

Just the Basics

The more open your lens is, the more light comes in to your camera. Aperture is specified using f/number, where a smaller number means more opening. So f/2.8 is faster than f/5.6, we also discuss this trade-off under ISO. At least in theory, the fastest lens setting is the best. It allows more light, so you can either use a faster exposure time helping you to capture faster moving things, compensate for movement of the camera while taking a picture (that helps with sharpness or allow you to use a less noisy ISO setting.

But there is more to the story

Practically all lenses allow you to control the aperture, it is one of the basic settings. There is the maximum you can open the lens, this is the f/number that the lens is known with.

So why would you want to control the aperture:

  • Controlling the depth of field, An open lens collects a lot of light at the distance it is focused on and an area just around this point. The picture is sharp where it is focused, but blurred everywhere else. This can be used to tell the viewer where to look at, it can be a very powerful artistic tool.
  • Lenses are not at their best performance when fully open. The basic problem of a wide open lens is falloff, that the corners of your image do not get the same amount of light as the center part of the image. Stepping up, or closing the aperture will usually help in this case. Most lenses are also a bit sharper with smaller apertures, before diffraction kicks in, and makes the image softer again.
  • And sometimes, there is just too much light. Lenses that are open collect a lot of light, and sometimes they would need a exposure time that is shorter than your camera can manage. There are also cases (waterfalls, propellers) where you may want a specific exposure time, where adjusting the aperture could help.
Extreme example

This shot (see more below) shows the effect of aperture on the depth of field. This is an extreme example taken by the Nikon 105 macro lens, which can get very close, the focus in this picture is about 40cm away from the sensor. This exaggerates the effect. Chip f3.5.jpg This is the most wide open setting for this lens at this distance f/3.5, the exposure time is 1/20s. Notice that only a very narrow part of the picture is in focus.

Chip f40.jpg This is the most wide open setting for this lens at this distance f/40, the exposure time is 5s, 100 times more than the previous one. Most of the frame is now in focus, but we needed 100 times longer to capture the picture.


More example pictures

You will see the interplay between the aperture and depth of field. Just look at the right hand side for the distance markers on the green ruler (they are in mm scale), to see what is in focus.


These pages are for Amateur Photographers and not really for seasoned photographers and professionals. I have no affiliation or commercial interest with any brand/make. I write from my own experience. I ended up using mainly Nikon, so I am more familiar with this brand than others. See price for notes on pricing as well as photography related links.

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