# Aperture priority vs Auto (or Program) mode



## xenocide (Dec 7, 2010)

Hello, 

I recently purchased a Pentax k-x camera as an upgrade over a Canon PowerShot G9. The majority of my pictures are nature and landscape. One thing I wondered about is that most pictures I see on Flickr of the same kind of material shows that people shoot in Aperture Priority mode a lot. I know that this mode can be  a useful tool for having control over the Depth of Field, but why would I use it as my base mode if I am not trying to do anything special with my subject?

For example for a normal landscape shot like this:






I'll concentrate more on composition and lighting and let the camera deal with DoF, which it does just fine.


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## Derrel (Dec 7, 2010)

Well, on the freeway with a car with an automatic transmission, Drive will usually give you the exact right gear for the conditions...on a 4-speed, most of the time it'll keep it in 4th gear...if you step down really hard and long on the accelerator, the transmission might very well shift into 3rd gear...on a steep, uphill grade, the transmission will shift into 3rd, then open up the fuel injection system wide-open and really pour fuel to it as the difficulty of climbing intensifies...heck, it might even drop down to 2nd gear nearing the crest of a really LONG, slow climb with a load being towed...

THAT is Aperture Priority Automatic...


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## Chamelion 6 (Dec 7, 2010)

It's still about control.  By using AV you are still giving some thought about how the lens is going to "see" the image, where as P or Auto the camera is making ALL the decisions for you.

I personally bounce back and forth between my modes depending on what I'm shooting, but probably spend most of my time in AV.  Unless you shooting a swiftly moving subject and want to freeze it, your aperature is probably the most noticable setting in your image.  When I shoot landscapes like this I tend to use AV mode most of the time.   In the old days on my A-1's I used the "stop-down" to prefiew the scene and adjust the aperature...  Now I just shoot it and adjust.


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## Overread (Dec 7, 2010)

f5.6, ISO 100, 1/200sec
no matter what mode you shoot in those settings will give the exact same result to the photo (provided all other things remain the same as well). What matters however is both how you arrive at those settings and if they are the correct settings for the shot you want to create.

With any scene there are 8 possible combinations of ISO, aperture and shutter speed - each of which will produce a correctly exposed shot - which one is right for you however will depend on the kind of shot you want to create. Further there are going to be many times when you want to over/under expose from the meters suggested reading - either because the meter is being tricked by the scene to over or under expose (eg shooting the moon or snow) or because you delibratly want an under/over exposed shot. 

Thus this is why you have semi auto and full manual modes as well as the full auto mode and why having some control over the camera's settings is key to creating the final composition and exposure that you want.

I strongly recommend you get the book "Understanding Exposure by Bryan Peterson" and read through and to the exercises. Gain enough control with the camera to be able to shoot comfortably in most modes up to and including manual mode - then you are empowered to make the mode choice that is best for you; and further you are able to understand what the settings will mean in a real world shot to yourself


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## KenC (Dec 7, 2010)

Actually, Overread, there are a lot more than 8 combinations, but that fact just amplifies your point that one needs to understand all the possibilities and make choices accordingly.  In your example, just at ISO 100, in addition to 5.6 & 1/200 you could have 4 & 1/400, 2.8 & 1/800, 2 & 1/1600, 8 & 1/100, 11 & 1/50, 16 & 1/25, 22 & 1/12 plus additional ones if you have a faster lens and/or faster shutter speeds available, in addition to the ones intermediate between these full-stop differences.


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## Patrice (Dec 8, 2010)

I've seen a few friends boast of always using their camera in manual mode. They meter the scene and set the aperture and shutter to match the meter. This is not really manual mode now is it? Once you start changing the exposure differently than what your meter tells you is correct then you start to take control. 

In full auto mode the camera will decide all the parameters leaving very little control to you.

In program mode the camera will analyze the scene and then set aperture and shutter according to the comparison it makes with a set of similar conditions in a data bank. You then have the choice, via the jog wheels, of changing either the aperture or shutter while the camera keeps the same exposure by changing the other setting. To vary the exposure you have to use exposure compensation.

In aperture or shutter priority you set the desired value and the camera will set the other to achieve the correct exposure according to it's meter reading. To vary the exposure you again have to use exposure compensation.

In manual mode you select an aperture and shutter and click away. If you set your controls to agree with what your meter says is good, well then you might as well stay in one of the auto modes.


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## xenocide (Dec 8, 2010)

Patrice said:


> In manual mode you select an aperture and shutter and click away. If you set your controls to agree with what your meter says is good, well then you might as well stay in one of the auto modes.



interesting


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## table1349 (Dec 8, 2010)

Patrice said:


> I've seen a few friends boast of always using their camera in manual mode. They meter the scene and set the aperture and shutter to match the meter. This is not really manual mode now is it? Once you start changing the exposure differently than what your meter tells you is correct then you start to take control.
> 
> In full auto mode the camera will decide all the parameters leaving very little control to you.
> 
> ...



Except the camera doesn't have a brain and can not make a decision on what it will meter off of.  A human can and does.  Perhaps you should learn more about using manual mode and metering and you would understand.   I may take several meter readings of a scene in different areas and from experience and my own knowledge select my settings based upon a combination of those meter readings.  I also will use different metering modes for different portions of the scene.  The camera does not and can not do this.


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## Patrice (Dec 8, 2010)

gryphonslair99 said:


> I may take several meter readings of a scene in different areas and from experience and my own knowledge select my settings based upon a combination of those meter readings.  I also will use different metering modes for different portions of the scene.  The camera does not and can not do this.



:thumbup:
Exactly why manual mode exists!


edit: or I should have said that is why it is available on decent cameras. That was how it was done with a handheld light meter before in-camera meters and with cameras with simple 'match the needle' centre weighted meters.


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## Garbz (Dec 14, 2010)

gryphonslair99 said:


> Except the camera doesn't have a brain and can not make a decision on what it will meter off of.  A human can and does.



No one expects it to. I use my camera in aperture priority all the time, and the camera most definitely does know what it will meter of because I tell it what. You sound like you're throwing the baby out with the bathwater whereas the reality is that the analogy really doesn't apply because of the nature of every bit of technology in the camera.

Everything that is more advanced than a pinhole is designed to aid the user. Sure we can focus manually and guess our way through exposures and apertures etc, but in reality even the manual exposure can benefit with a guide. 

- Your guide may be an external light meter and your tool may be the control of shutter and aperture.
- My guide is the fact that I know my camera will select a shutter speed appropriately to what it thinks, based on the focus point I've selected, and my tool is the control of focus point and the exposure compensation slider. 

Both get us to the same end. 



xenocide said:


> I know that this mode can be  a useful tool for having control over the Depth of Field, but why would I use it as my base mode if I am not trying to do anything special with my subject?
> 
> For example for a normal landscape shot like this:
> 
> I'll concentrate more on composition and lighting and let the camera deal with DoF, which it does just fine.



DoF is a component of compositional design. Your example image has no depth. It makes no difference to that picture whether you shoot at f/1.4 or f/22. In which case P mode is ideal. Let the camera guess away, as long as the final exposure value is the same it won't make a difference.

The reason you'll find a lot of people play with aperture priority is because for them aperture does play a roll. I instinctively will ignore the aperture if I'm shooting a picture such as the one you posted providing the shutter speed is right because for the most part, my last camera worked in aperture priority and didn't have a program auto mode. I find it far more of a hassle switching between modes than I do sliding a clickwhere to select a different aperture depending on the number I see in the viewfinder. 

It's also the reason why I would sooner reach for my AE-Lock button and my exposure compensation button than switch to manual if my camera doesn't do what I want it to. 

As I said above to gryph, the tools are there. How you use them is entirely up to you, and as long as they get you the shot you want in the way you want no one can tell you that you did it the wrong way.


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