A and S mode


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New Member
Sep 25, 2010
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#1
Hi guys..i got a few questions i wish to ask..hope can seek can help here ^^

i am using D5100 and i have tried out the A and S mode..from what i have read, i understand that for the A mode, we got control of the aperture and the system will control the shutter speed accordingly, and opposite for the S mode.

But i realised that when i changed the aperture in the A mode, the shutter speed will change accordingly..so no matters what aperture i change to, the exposure of the photo will look the same..? (same case for P mode)

I am wondering if the resulted exposure is going to be the same, then why do we need to manual change the aperture or shutter speed in the first place?

Is it because if we use a slower/faster shutter speed, the image will be blurred/freezed while the exposure remains the same(S mode)?
 

sinned79

Senior Member
Jun 18, 2009
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#3
u need more reading...

Some examples:
Aperture allows u to control the depth of field (blurred background vs sharp background)

Shutter speed allows u to freeze a fast moving subject or create some blurness in the background while freezing your subject (usually pan shots)

and because both modes are considered auto modes, the exposure is always the same cos the camera decides for u the exposure. u can however adjust the exposure manually also ( -1 , -2 , +1 , +2 etc)

RTFM.
 

Last edited:
Aug 16, 2010
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#4
Hi guys..i got a few questions i wish to ask..hope can seek can help here ^^

i am using D5100 and i have tried out the A and S mode..from what i have read, i understand that for the A mode, we got control of the aperture and the system will control the shutter speed accordingly, and opposite for the S mode.

But i realised that when i changed the aperture in the A mode, the shutter speed will change accordingly..so no matters what aperture i change to, the exposure of the photo will look the same..? (same case for P mode)

I am wondering if the resulted exposure is going to be the same, then why do we need to manual change the aperture or shutter speed in the first place?

Is it because if we use a slower/faster shutter speed, the image will be blurred/freezed while the exposure remains the same(S mode)?
Technically the exposure would be the same as it will go according to the camera's metering.
For your answer to why manually change the aperture and shutter speed in the first place is very simple. You just have to know what does aperture do and what does shutter speed do and you will have your answer.
 

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New Member
Sep 25, 2010
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#5
thanks for all the helpful replies :) it has cleared my doubt on the modes :)

regarding the depth of field, it means the blurring/focus of background if i'm not wrong?

so to achieve a blur-er(shallow DOF?) background, need to have large aperture, lens closer to subject and the distance between subject and background greater?
and to achieve a extensive(means all in focus?) DOF, the aperture has to be small..and..?

shorter-focal-length lenses, smaller apertures, and greater lens-to-subject distance all increase the range of sharp focus
- i read this line but i dun really understand the first and last point..
 

edutilos-

Senior Member
Dec 28, 2010
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#6
thanks for all the helpful replies :) it has cleared my doubt on the modes :)

regarding the depth of field, it means the blurring/focus of background if i'm not wrong?

so to achieve a blur-er(shallow DOF?) background, need to have large aperture, lens closer to subject and the distance between subject and background greater?
and to achieve a extensive(means all in focus?) DOF, the aperture has to be small..and..?

- i read this line but i dun really understand the first and last point..
To understand depth of field, you can think of everything in your frame as a 3D cube, where you can only see one 2D face. (since it's bounded by 4 lines)

Depth of field is not blurring and focus of background, but it is related. It's like taking a slice through that 3D cube, and rendering everything parallel to the sensor plane in focus. A smaller aperture yields greater depth of field and a thicker slice. A larger aperture yields smaller depth of field and a thinner slice.

When you use a large aperture and achieve a thinner slice, everything BEFORE and AFTER that slice will be OOF. Only things lying along the plane of the slice and within it will be in focus.

I hope this analogy is clear.
 

ziploc

New Member
Jan 17, 2002
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Snoopyland
#7
thanks for all the helpful replies :) it has cleared my doubt on the modes :)

regarding the depth of field, it means the blurring/focus of background if i'm not wrong?

so to achieve a blur-er(shallow DOF?) background, need to have large aperture, lens closer to subject and the distance between subject and background greater?
and to achieve a extensive(means all in focus?) DOF, the aperture has to be small..and..?

- i read this line but i dun really understand the first and last point..
Try this:

Put a magazine in front of your camera, as close as possible but still making sure it can focus. Now set your camera to A mode, set aperture to the widest (say f/3.5) and take a pic. Next set your aperture a few stops down (say f/8) and take a pic. Upload the 2 pics to your computer and you can see the DOF difference. Note the exposure value for these 2 pics (aperture and shutter speed).

Next to see the effect of the shutter speed. Find a moving fan in your house. Set your camera to S mode, set your shutter speed to 1/30s and take a pic. Next set your shutter speed to 1/500s and take another pic. Upload them to your computer and you can see the effect of the shutter speed.
 

ziploc

New Member
Jan 17, 2002
4,577
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Snoopyland
#8
shorter-focal-length lenses, smaller apertures, and greater lens-to-subject distance all increase the range of sharp focus
- i read this line but i dun really understand the first and last point..
The DOF (depth of field) is affected by 3 factors:
- focal length of your lens: the longer the focal length, the thinner the DOF
- lens to subjet distance: the closer the subject, the thinner the DOF
- the aperture size: the wider the aperture (low f-number, e.g. f/2.8), the thinner the DOF

See this page on DOFMaster and this page for the explanation of DOF.
 

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New Member
Sep 25, 2010
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#9
edutilos- said:
To understand depth of field, you can think of everything in your frame as a 3D cube, where you can only see one 2D face. (since it's bounded by 4 lines)

Depth of field is not blurring and focus of background, but it is related. It's like taking a slice through that 3D cube, and rendering everything parallel to the sensor plane in focus. A smaller aperture yields greater depth of field and a thicker slice. A larger aperture yields smaller depth of field and a thinner slice.

When you use a large aperture and achieve a thinner slice, everything BEFORE and AFTER that slice will be OOF. Only things lying along the plane of the slice and within it will be in focus.

I hope this analogy is clear.
Hi regarding this analogy.. Then how should I determine where to cut the slice? Like in the middle or towards the end etc..
 

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New Member
Sep 25, 2010
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#10
Thanks for all the replies.. Having a better view and and trying out the diff modes :)
 

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