What's the diff between shutter and apperture priority?

[doanster]

Any photo gurus here?

 

[imported_Stew]

Shutter Priority= You set the desired length of exposure, the camera chooses the rest. (e.g., you need a very fast shutter speed so you set your camera to 1/125 and the camera will choose a wide aperture to be able to achieve that best)
Aperture Priority= You set the desired aperture, the camera chooses the rest.

Correct me if I'm wrong.

 

[Aosh]

Absolutely correct. 3 factors to exposure: ISO, aperture, shutter speed.

You can think of exposure as filling a cup.
-Aperture is the size of the opening letting light (water) in.
-Shutter speed is how long you let the light / water flow in.
-ISO is how big the cup is. A high ISO (like ISO 1600) means the sensor/film is very sensitive to light. So you need less light to make a proper exposure, thus it's a small cup.

Now say we have a given ISO. For some aperture, there is always a corresponding shutter speed that will precisely fill the cup (give you the proper exposure) and vice versa.
So in shutter priority, you tell it how long you want the light coming in, and the camera will choose the right aperture.
In aperture priority, its the opposite: you tell it how big you want the hole of light coming in, and the camera will choose the length of time to let it in.
You (or the film) chooses the ISO in both cases.

Aperture priority is usually more useful unless you have a specific speed you want (usually for creative long exposures). If you want the fastest shutter speed possible, then just set the aperture to be the widest the lens will permit it to go.

 

[foges]

Originally posted by: Stew
(e.g., you need a very fast shutter speed so you set your camera to 1/125 and the camera will choose a wide aperture to be able to achieve that best)
.

Correct, one thing though: Most photographers wouldnt consider 1/125 second to be very fast, it may be strange, but thats actually quite slow. My 20D for example goes up to 1/8000 sec

 

[RebateMonger]

The most common automatic exposure mode nowadays is "Programmed Mode". It is neither shutter- nor aperture-priority. Rather, it uses pre-programmed choices combining changes in both shutter and aperature. The goal is to keep a reasonable balance between shutter speed and aperture. But to not allow the shutter speed to get so low that fuzzy photos are likely.

 

[Lemon law]

A few more factors

Given that the photographer---in most situations---cannot control light levels---then one must shoot with the natural light you have---with film you can choose a faster
film--in a digital camera you are stuck with the speed of the sensor factory installed.


Because you must get the right amount of light for the film or sensor---your tradeoffs become---in general 1/60 of second or longer of a duration shutter speed and the average person will not be able to free hand hold the camera steady---so you may be talking tripod or a blurred picture.---and forget about freezing any motion---but as pointed out earlier
its SOMETIMES creates a pleasing surrealistic effect---but ALWAYS fails to portray reality.

If on the other hand you want to open your lens up to admit the most possible light---so your shutter is open for a shortest duration you do so by choosing the lowest numerical F stop the lens is capable of---your depth of field---or the relative distance where two objects of differing distance from the camera lens can both be in focus in the same picture is also sharply reduced---and that not in focus will appear blurred---sometimes that blurring can enhance the picture by say blurring a distracting background or foreground---but its still not reality.

So the important thing to realize is that its a tradeoff---you can't have your cake and eat it too---and if you don't like it---you better artificially add light--or wait for a brighter day.

And if the light level is low--sometimes there is no acceptable trade off.

 

[foges]

I dont think that many people use P-mode though, cause if you dont know anything youll probably use green box mode, if you know a bit more youll probably want to be in controll over the appeture or shutterspeed, p-mode is what i give my dad to take photos 😀

Re: Lemon law

Get the 5D which is really good at high ISO's 😛