# What is Difference Between P mode and A mode in Nikon D3100



## bhaur (Feb 28, 2012)

In Nikon D3100, both P mode and A mode give control on Aperture. In both modes, shutter speed is calculated on the basis of the selected aperture. So what is the difference between both?
Thank you.


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## MTVision (Feb 28, 2012)

bhaur said:
			
		

> In Nikon D3100, both P mode and A mode give control on Aperture. In both modes, shutter speed is calculated on the basis of the selected aperture. So what is the difference between both?
> Thank you.



&#12539;Mode P (Programmed Auto)
The camera automatically adjusts aperture and shutter speed for optimal exposure, but the photographer can choose from different combinations of aperture and shutter speed that will produce the same exposure. This is known as flexible program.

&#12539;Mode A (Aperture-Priority Auto)
The photographer chooses the aperture and the camera automatically adjusts shutter speed for optimal exposure.
Notethat in all three modes&mdash;P, S, and A&mdash;exposure is automatically adjusted for optimal results.


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## djacobox372 (Feb 28, 2012)

P doesn't let u control the aperture.


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## scorpion_tyr (Feb 28, 2012)

Select the desired aperture in P mode, then take a picture. Now take another picture, and chances are the aperture will now be different. Turn it to A, and select an aperture, now it will remain that aperture until either you change it or your lens no longer allows that f/stop at a new focal length. P basically selects a random shutter speed and f/stop combination based on the selected ISO and your exposure bias. It does this everytime you meter. A lets you determine the f/stop and keep the same one and whenever conditions change, the shutter speed will be the only thing changed.


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## bhaur (Feb 28, 2012)

djacobox372 said:


> P doesn't let u control the aperture.


"Rotate the dial to the right for large apertures (low f-numbers) that blur background details or fast shutter speeds that freeze motion. Rotate the dial to the left for small apertures (high f-numbers) that increase depth of field or slow shutter speeds that blur motion."
A quote about P mode from user manual of camera.


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## 2WheelPhoto (Feb 28, 2012)

P then A gets one close to the real mode to use called "M"   =)


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## bhaur (Feb 28, 2012)

scorpion_tyr said:


> P basically selects a random shutter speed and f/stop combination based on the selected ISO and your exposure bias. It does this everytime you meter.


Thank you for your response. It was the most helpful.
So is it so that the combination of shutter speed and f/stop is absolutely random, every time?


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## punch (Feb 28, 2012)

depends... you can set your ISO to auto as well.

i don't shoot nikon, but in the canon, you can use program shift in P but not A (you can adjust aperture or SS as you like on the fly) and the flash won't pop up in P like it will in A.


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## 480sparky (Feb 28, 2012)

djacobox372 said:


> P doesn't let u control the aperture.



Yes it will.  It simply adjusts the shutter speed to compensate.

Page 74 of the manual:

Flexible Program
In mode P, different combinations of shutter speed and aperture can be selected by rotating the command dial (&#8220;flexible program&#8221. Rotate the dial to the right for large apertures (low f-numbers) that blur background details or fast shutter speeds that &#8220;freeze&#8221; motion. Rotate the dial to the left for small apertures (high f-numbers) that increase depth of field or slow shutter speeds that blur motion. All combinations produce the same exposure. While flexible program is in effect, a U (R) indicator appears in the viewfinder and information display. To restore default shutter speed and aperture settings, rotate the command dial until the indicator is no longer displayed, choose another mode, or turn the camera off.




scorpion_tyr said:


> .. P basically selects a random  shutter speed and f/stop combination based on the selected ISO and your  exposure bias..........



It doesn't select a 'random' shutter speed, it selects one based on the light level, the max aperture of the lens and the focal length of the lens.  If you zoom in, the shutter speed will increase.  If the shutter speed drops below an average "hand-held" speed, it will open the aperture and/or increase the ISO.


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## punch (Feb 28, 2012)

P.S. don't use P or A... they often choose wrong for you.


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## MTVision (Feb 28, 2012)

bhaur said:
			
		

> "Rotate the dial to the right for large apertures (low f-numbers) that blur background details or fast shutter speeds that &#147;freeze&#148; motion. Rotate the dial to the left for small apertures (high f-numbers) that increase depth of field or slow shutter speeds that blur motion."
> A quote about P mode from user manual of camera.




From what I understand the camera is metering the scene and coming up with a decent exposure. You can change the settings with the command dial - but you are changing BOTH aperture and shutter speed but keeping the same exposure the camera determined. It lends you a little creative control by letting you decide if you want more depth of field or if you want to blur motion.


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## Ysarex (Feb 28, 2012)

In A mode you're specifically selecting the f/stop. The camera will then measure the available light and accounting for the set ISO, calcualte and set the shutter speed required for correct exposure. Throughout this process the f/stop stays locked where you have set it -- A mode priority.

In P mode the same measuring process takes place. The camera meter calulates the correct exposure by measuring the available light and, accounting for the set ISO, it determines a shutter speed and f/stop combination. This determination is in not at all random, but based on a program embedded in the camera's software. This program is biased toward shutter speeds sufficiently fast enough to allow hand-held photogrpahy.

 With your camera, as is typical of modern electronically controlled cameras, you can simply rotate a wheel on the camera and force the camera to rotate through the entire set of shutter speed, f/stop combinations available with your camera body and lens that will produce the same exposure. This is in fact the most efficient method of using the camera provided you intend to rely on the camera's internal metering system.

Put the camera in P mode and then select the f/stop/shutter speed combination that you assess as most appropriate for the photo.

Back to your original question: If in A mode on a sunny day with the ISO set to 100 you set the f/stop to f/11 the camera should select a shutter speed close to 1/250 sec. which would be a correct exposure. In P mode on a sunny day with the ISO set to 100 the camera will select both an f/stop and shutter speed for correct exposure. If you rotate the control wheel until the f/stop is f/11 you'll find the shutter speed is exactly the same as if you had set the camera to A and locked the f/stop at f/11. So it's really a case of how you want to approach or think about controlling the camera. The end result is the same.

Joe


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## Ysarex (Feb 28, 2012)

bhaur said:


> scorpion_tyr said:
> 
> 
> > P basically selects a random shutter speed and f/stop combination based on the selected ISO and your exposure bias. It does this everytime you meter.
> ...



Absolutely not. The camera's choice of shutter speed and f/stop in P mode is never random. P stands for program and in P mode the camera is following exactly that -- a program which always produces specific and repeatable results. That program is well designed and carefully thought out and it repeatably delivers the results it's designers intended.

There are assumptions built into various camera's Program modes of operation. One typical assumption is that the camera is being used hand-held and so the program is biased to keep the shutter speed high enough to support hand-held photography.

Joe


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## bhaur (Mar 1, 2012)

Ysarex said:


> This determination is in not at all random, but based on a program embedded in the camera's software. This program is biased toward shutter speeds sufficiently fast enough to allow hand-held photogrpahy.
> 
> Joe



This is what I wanted to know. Thanks.


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## Redeyejedi (Mar 1, 2012)

the camera will match the change you make with an equivlant exposure in the auto/semi-auto modes. this may or may not be your desired result when considering other aspects of the shot than exposure; DoF, motion control, etc.
 so, as i understand it, Program, Shutter and Aperture modes will yield the same exposure value, but may have different yet equivalent exposures, basically giving the artistic control away to the camera.


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## Ysarex (Mar 1, 2012)

Redeyejedi said:


> the camera will match the change you make with an equivlant exposure in the auto/semi-auto modes. this may or may not be your desired result when considering other aspects of the shot than exposure; DoF, motion control, etc.
> so, as i understand it, Program, Shutter and Aperture modes will yield the same exposure value, but may have different yet equivalent exposures, basically giving the artistic control away to the camera.



You do not give artistic control to the camera by using P, S or A modes. In fact with the camera mentioned by the OP, unless you are using external flash or an external metering source, it's fair to argue that you gain maximum artistic control with the camera in Program mode. Maximum artistic control is afforded by maximum efficiency. The less you have to do to physically adjust the camera to reach your desired exposure parameters the more time and energy you have to devote to artistic control. P mode has the efficiency edge -- it may be slight but an edge is and edge.

Joe


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## ph0enix (Mar 1, 2012)

OP: Please read pages 72-76 in your camera's manual.  Here it is in PDF format in case a hard copy didn't come with the camera:
http://www.nikonusa.com/pdf/manuals/kie88335f7869dfuejdl=-cww2/D3100_EN.pdf


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