How does aperture works?


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Scandiacus

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Jun 27, 2008
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Hougang
#1
Okay this has been bothering me for quite sometime since I start to learn photography.

As far as I know, the aperture's main function is to control the amount of light reaching the focal plane as well as the depth of field but why doesn't closing the aperture blades blocking up the image itself and resulting in a image when a black round border around it? :dunno:
 

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zzyzx

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Aug 25, 2007
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#2
the sensor doesn't capture what it sees in front but rather receive whatever comes onto it.

think of it like this... comparing when you pour a pail of water thru a funnel with smaller opening above a tray and a funnel with a bigger opening at a similiar given time, the tray with the funnel having the bigger hole will collect more water. now if you understand this, then replace the water with amount of light, and the opening of the funnel with aperture opening.

get it?
 

Scandiacus

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Hougang
#3
the sensor doesn't capture what it sees in front but rather receive whatever comes onto it.

think of it like this... comparing when you pour a pail of water thru a funnel with smaller opening above a tray and a funnel with a bigger opening at a similiar given time, the tray with the funnel having the bigger hole will collect more water. now if you understand this, then replace the water with amount of light, and the opening of the funnel with aperture opening.

get it?
Sort of but, why don't the light from the object get all absorbed by the aperture blades when the hole's really small? :dunno:
 

attap seed

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Feb 16, 2006
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#4
the pupil of your eyes and the lens aperture work on the same principle.
 

Scandiacus

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Hougang
#5
the pupil of your eyes and the lens aperture work on the same principle.
I know, but, why won't we get tunnel vision when our pupil is really small in bright light, and same goes to a camera? :dunno:
 

night86mare

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Aug 25, 2006
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#6
Okay this has been bothering me for quite sometime since I start to learn photography.

As far as I know, the aperture's main function is to control the amount of light reaching the focal plane as well as the depth of field but why doesn't closing the aperture blades blocking up the image itself and resulting in a image when a black round border around it? :dunno:
did you get to play with pinhole camera last time in school?
 

ahliang

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Nov 23, 2007
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#9
Light coming onto sensor is in all directions.
 

lrrp77

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Mar 10, 2004
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#10
Think of it as the iris in your pupil changing focus.

The aperture blades do not close like your eye lids. That will be the lens "cover" :)
 

lsisaxon

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Nov 29, 2004
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#12
I know, but, why won't we get tunnel vision when our pupil is really small in bright light, and same goes to a camera? :dunno:
Do you get tunnel vision under bright sunlight? I don't. ;p

Anyway, it has to do with where the aperture diaphram is located.
 

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Jul 31, 2006
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#13
It is because you assume that everything in front of the lens (or at the middle of it) will leave its image on the sensor, which is not true.

Only things those are near to the focused object will leave their images on the sensor. Things those are not with in the DOF will leave blur images. If you observe carefully, those blur images are half transparent.

In extreme cases, there are some positions that any objects placed there will not leave the images on sensor at all. For example, right at the center of each lens. Draw something on your UV filter, then put it near the front element of your lens, then take picture, you will know what I mean.

The apreture blades are placed at such a position, therefore, it can block the light as well as control aperture without leaving any image on sensor.
 

raaj.cee

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Nov 7, 2006
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#15
Okay this has been bothering me for quite sometime since I start to learn photography.

As far as I know, the aperture's main function is to control the amount of light reaching the focal plane as well as the depth of field but why doesn't closing the aperture blades blocking up the image itself and resulting in a image when a black round border around it? :dunno:
The aperture is only an opening to allow light to reach the sensor/film. Light reaches the sensor through the aperture and for the sensor it can be said that the aperture is similar to a light source. Therefore, no black borders.

Ahh I see, I'm starting to get the picture (no pun intended), thanks guys ;)


Anyway, my curiosity sprouted when I saw this web page on custom made bokeh

http://www.diyphotography.net/diy_create_your_own_bokeh

The custom heart shaped aperture left me wondering why won't the image be blocked :think:
In this case, changing the shape of the aperture affects the image formed on the sensor. In the parts of the image that are in sharp focus, these aberrations are not noticeable but on the bokeh they are.
 

lsisaxon

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Nov 29, 2004
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#16
Ahh I see, I'm starting to get the picture (no pun intended), thanks guys ;)


Anyway, my curiosity sprouted when I saw this web page on custom made bokeh

http://www.diyphotography.net/diy_create_your_own_bokeh

The custom heart shaped aperture left me wondering why won't the image be blocked :think:
You can try but I'm quite sure the image will be blocked with wide angle lenses. ;p
 

calebk

Senior Member
Jul 25, 2006
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Clementi
#17
Bro night86mare has the best answer. A picture speaks a thousand words. The smaller the opening (aperture), the least the diffusion and thus obtaining sharper image with maximal DOF.
Diffusion?! :eek:
 

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