Photography - Aperture?

Question

If i increase my shutter speed , do i have to do anything with the apeture like increase , decrease or somthing

Answer 1

Yes, when you increase the shutter speed by a stop, you have to open the aperture by a stop, it's as easy as that. Because if you continue upping the shutter speed without adjusting the aperture, you're going to get some under-exposure.

Answer 2

The aperture and shutter are but two legs of the exposure triangle. ISO is the third leg.

ISO: a measurement of the sensitivity to light of a light sensitive surface, whether film or digital sensor. A slow ISO (50, 100) is very insensitive and requires a lot of light. A fast ISO (400, 800, 1600) is very sensitive and requires much less light.

Aperture (aka f-stop): an opening formed by the movable blades of the diaphragm inside the lens. A large f-stop (f1.2, f1.4) is a large opening and admits all the light. A small f-stop (f8, f11, f16) is a small opening and admits very little light. The size of the aperture also controls Depth of Field (DOF) - a topic best left for another day.

Shutter: determines how long the light admitted is allowed to expose our light sensitive surface, whether film or digital sensor. The shutter speed also determines whether motion in our scene will be blurred or stopped. A fast shutter speed (1/250, 1/500, 1/1000) will usually stop any motion. A slow shutter speed (1/4, 1/2, 1/15) will cause any motion to be a blur.

Back before in-camera meters were common and few people owned a hand-held light meter, the "Sunny 16 Rule" was invented. It states: "On a sunny day, set your f-stop to f16 and your shutter speed to 1/ISO."  So if you were using ISO 100 you could expect good exposures at f-16 @ 1/125 sec.* Look at the following example to see the f-stop/shutter speed/ISO relationship using the "Sunny 16 Rule."

ISO 100

f16 @ 1/125

f11 @ 1/250

f8 @ 1/500

f5.6 @ 1/1000

f4 @ 1/2000

f2.8 @ 1/4000**

f2 @ 1/8000**

ISO 400

f16 @ 1/500

f11 @ 1/1000

f8 @ 1/2000

f5.6 @ 1/4000**

f4 @ 1/8000**

f2.8 @ 1/16000**

f2 @ 1/32000**

As you can easily see, increasing shutter speed requires that you "open up" your aperture. Decreasing your shutter speed requires you to "stop down" the aperture.

I shoot in Aperture Preferred 99% of the time because I like to have a lot of DOF. I watch the shutter speed the camera selects to make sure its not too slow for me to hand-hold the camera.

* The "Sunny 16 Rule" was invented when cameras were 100% mechanical. Your shutter speeds were non-variable so we used the closest approximation - 1/125 for ISO 100, 1/500 for ISO 400, etc. The modern electronically controlled shutter is effectively "stepless" and will more closely approximate the 1/ISO.

** These speeds are beyond the capability of most cameras.  

Answer 3

Increase shutter speeds means open aperture.  Lower shutter speeds mean closing aperture.  The size of the aperture determines the amount of light coming in through the lens.  

Answer 4

If you set the camera on Tv and set the shutter speed the camera will set the aperture for you.  If you increase the shutter speed you are decreasing the time that the sensor exposed to light so yes you will have to open the aperture more to compensate for that.  

Answer 5

Linked below is an exposure calculator so you can see for yourself.

In short....  A smaller f/stop is a larger aperture opening and a smaller depth of field.  Confusing.  So, easier, smaller f/stop = smaller depth of field.  A smaller aperture also means a faster shutter speed can be used, which is why lenses with a small f/stop are referred to as "fast" lenses.

If you have an Aperture priority (Av) or Shutter priority (Tv) on your camera, play around with it.  In Av, as you change the aperture the camera measures the lighting and will change the shutter speed accordingly.

Also play around with the exposure calculator linked to below.

Answer 6

Aperture and shutter speed work together to let just the right amount of light through to the film/sensor.

If the meter says 1/100th of a second at f8 then 1/50th of a second at f16 would let exactly the same amount of light through. You have let half the amount of light through for twice the time.

Aperture controls the depth of field, so if you want to isolate the subject from the background you would use the widest aperture you have say f2.8, with the meter reading as above that would give you 1/300th of a second. Conversely if you want to have a greater depth of field such as in a landscape you would use f16 (or even smaller).

That's why most photographers use Aperture Priority setting on their cameras as it enables you to quickly select the aperture you want, the camera will work out the correct shutter speed for you (within limits - they don't always get it right, but that's a different question).

All lenses have a 'sweet spot' when it comes to aperture usually at f8 or f11, but it can vary when you alter the zoom.

Chris