# program mode VS ap/shutter priority?



## JCphoto (Dec 19, 2010)

I'm confused as to the difference between using program mode and using aperture or shutter priority.

It seems to me that program mode is like having both aperture and shutter priority at the same time. The only thing that would make sense to me is if program mode restricts control over something im not aware of, though any camera manual I have checked just mentions aperture and shutter speed.

thanks for the help!


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## Overread (Dec 19, 2010)

In aperture and shutter priority however you have direct control over one setting - whilst also being able to use exposure compensation to tell the camera to compensate the other setting to over/under expose from the meter reading. 

Now if you're just wanting a good exposure with no creative restrictions then P mode works perfectly well - however many times you'll want some creative control over your shot. Maybe you're shooting propeller planes and want to blurr the rotors - so you go into shutter priority mode and set 1/60sec or slower and keep it at that speed - letting the aperture (and ISO) be based off that fixed reference point.

For a more indepth understanding I strongly recommend teh book Understanding Exposure by Bryan Peterson - this will got a long way to helping you understand the creative implications of the settings whilst also learning how to effectively use them as well as come to understand what a "correct exposure" actually is.


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## Garbz (Dec 20, 2010)

The reason they exist is to provide the user with automatic exposure while still being able to control composition. Some elements of composition include depth of field and motion blur. 

Aperture priority provides control over the aperture and thus depth of field whereas the camera will select the shutter speed to make the right exposure.
Shutter priority provides control over the shutter and thus control over motion blur while the camera will select the aperture to make the right exposure.
Program mode will give complete control to the camera for times where you really couldn't give a rats, or times where you know neither depth of field or motion blur are compositionally important (such as photographing a landscape on a sunny day, or getting pissed at the pub)


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## Derrel (Dec 20, 2010)

JCphoto said:
			
		

> It seems to me that program mode is like having both aperture and shutter priority at the same time.



Yes, that's a good way to look at it. Spin one wheel, and shift both aperture and shutter in lock-step. Quickly. Almost effortlessly. ESPECIALLY on simplified, so-called "one-button" cameras, like low-end Nikon or Canon bodies that lack a dedicated, single-use button for aperture adjustment.


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## Big Mike (Dec 20, 2010)

If you can keep your eye on your settings and your meter, it doesn't really matter which automatic/priority mode you are in...because if you change one setting, the other changes as well.  

For example, when I use a priority mode, it's almost always Aperture Priority.  So when a fast shutter speed is the most important choice for my photo, I just set a large aperture rather than going to shutter priority.


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## JCphoto (Dec 20, 2010)

I completely understand how the components work together (DoF, motion blur, etc.) my only confusion lies within the limitations of program mode itself.

After playing with program mode a bit just now i think i answered my own  question, it doesn't seem that i can change the exposure compensation.  which in hindsight makes sense, making program like an adjustable auto  mode, which i realize now is how people try to describe it.



Overread said:


> Maybe you're shooting propeller planes and want to blurr the rotors - so you go into shutter priority mode and set 1/60sec or slower and keep it at that speed - letting the aperture (and ISO) be based off that fixed reference point.



If that was the case and i was already in program mode, would it not make more sense to just change the shutter speed while still in program mode? why would I change modes when the program mode will adjust the aperture to compensate the same way shutter priority would.(my iso is locked at 100) The only situation that you would change modes that would make sense to me, is if your camera wasn't metering the scene to your liking, in which case you would be forced to change to another mode which allows for exposure compensation.

Am I on the right track here?

I shoot landscapes. Always using a tripod. (unless its completely unnecessary, which is rare) and i have my iso locked at 100. So i usually just leave my camera on aperture priority set at between f16-f20. Usually the only thing i need to worry about is if my shutter speed is to my liking, if it isnt i do as Big Mike says and either open up my aperture or add a neutral density filter to compensate. Regardless of my settings i try to always rely on my histogram to ensure a correct exposure.

Thanks again for the help everyone!


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## ann (Dec 20, 2010)

Program mode is just a 1/2 step up from full auto IMHO, you can change ISO and white balance.
The other function are light depended and are clueless what you what to do with your image.

Aperture/shutter priority functions all allow the photography to control DOF and of course blur or lack of blur.  They are connected of course, but the photographer is now in control and  not the "chip", that only makes a decision on light not on vision.


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## JCphoto (Dec 20, 2010)

yea, I guess I forgot to add that I adjust the exposure to my liking using exposure compensation, I don't assume the camera always knows the exposure I am looking for.


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## Garbz (Dec 21, 2010)

JCphoto said:


> So i usually just leave my camera on aperture priority set at between f16-f20.



This is off-topic but something relevant to your interests. On a D70 (according to your profile) diffraction starts becoming quite relevant to the sharpness of images beyond f/11. Ultimately it's still a composition related query, do you sacrifice large depth of field for far greater sharpness or not. If DoF is ever not relevant I don't recommend shooting above f/11 as you won't be doing your pictures any favours.


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## JCphoto (Dec 21, 2010)

Thanks for the tip Garbz, 

I knew diffraction kicked in somewhere in there... though I didn't realize it was as low as f11. I will keep that in mind for when DoF isn't an issue, although I'm very often shooting scenes involving water, which is usually what determines my decision on aperture, rather than DoF. Though I find, as long as the image is pretty sharp, photoshops sharpening tools (I prefer smart sharpen) can do an excellent job of crisping up those lines, my prints come out tack sharp even on shots where I needed an f stop of 22, so sometimes I wonder how much you really need to worry about minor diffraction, with today's processing software available. (assuming you're use it properly)


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## Allen (Dec 21, 2010)

Garbz said:


> JCphoto said:
> 
> 
> > So i usually just leave my camera on aperture priority set at between f16-f20.
> ...



Wouldn't that be dependent upon the lens hanging off the front of the camera and not the body?


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## Garbz (Dec 22, 2010)

JCphoto said:


> so sometimes I wonder how much you really need to worry about minor diffraction, with today's processing software available. (assuming you're use it properly)



Sharpness and visual acutance are two different things. We the people will perceive sharpness when contrast exists at a border regardless of the width of the border or any detail lost. A sharp image can benefit from light sharpening. In reality for most photos it won't make the tiniest difference. 

I have a couple of landscapes blown up 40" wide on the wall. The difference between actual sharpness and a sharpened image would be visible on that. Probably not really entirely field relevant but do remember that if you're trying to get the best performance, wondering why your new expensive lens isn't much sharper than your kit lens, or if you become one of those crazy people who sell images in a gallery that cost more than many cars. 



Allen said:


> Wouldn't that be dependent upon the lens hanging off the front of the camera and not the body?



Diffraction is governed by fundamental constants of the lens design (the width of the iris and projection distance to the sensor). What is left after that is the physical size of the pixels on the sensor. These are smaller naturally for cameras of the same resolution of a physically smaller sensor size. Thus diffraction depends on the sensor size and resolution only. So a point and shoot camera may be sharpest at f/5.6 after which diffraction will set in. A typical APS sensor DSLR diffraction becomes field relevant beyond around f/11, and on a full frame camera at f/16 and up.

This is a basic explanation. Some lenses are incredibly sharp and you'll see they peak much earlier and many are sharpest at f/8 on a typical DSLR with APS sized sensor. Also in reality diffraction also depends on viewing the image. A 6x4" image held at arms length effectively renders diffraction irrelevant. Blow up the image massively and diffraction becomes an issue as soon as the peak sharpness of the lens drops. 

Again how relevant this is ultimately is for you to decide, but in general take a look at a perfectly infocus f/22 picture and compare it to a f/11 picture and you should see more sharpness in the larger aperture despite the common belief that stopping down will increase sharpness.


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