Camera settings?

Question

Hi, I have a Canon PowerShot A570 IS. Recently I've been playing around with some of the different settings, and have figured out some cool stuff to do with slowing the shutter speed, however I still don't understand the aperture setting. What is the effect on the picture from increasing or decreasing the aperture? When should I use a high aperture, and when should I use a low one? Also, anybody with a similar camera (or familiar with this one), what other interesting stuff can I do besides "time lapse" type photos and messing with the aperture? I need some inspiration and information on how to do it...thanks!

Answer 1

Inside the lens there is the diaphragm. The diaphragm is made up of thin curved metal blades which can open and close to form an opening. This opening is called the aperture or f-stop. The numbers on your lens - f2.8, f4, f5.6, etc. - are the size of the f-stop opening in the diaphragm. It is an inverse relationship - the smaller the number the bigger the opening. If you have your lens at f2.8 its considered "wide-open" and admits all the light available. At f16 the lens is considered "stopped down" and very little light is admitted.

The aperture, along with the ISO you use, controls the shutter speed. Since ISO is a measurement of the sensitivity to light of a light-sensitive surface, film or digital sensor, the higher the ISO the more sensitive the surface and the less exposure to light it needs. There is, however, a trade-off - the higher the ISO the more "digital noise" and the lower the image quality. If your camera has "noise reduction" you should use it with higher ISO settings. If it doesn't, there are programs that will help in post-processing.Your shutter speed determines how long the light admitted by the lens is allowed to expose the light sensitive surface.

The following examples are purely hypothetical for examples only. The relationships are valid but may not exist in the real world. We are shooting outdoors on a sunny day.

ISO 100

f2.8 @ 1/500 sec.
f4 @ 1/250 sec.
f5.6 @ 1/125 sec.
f8 @ 1/60 sec.
f11 @ 1/30 sec.
f16 @ 1/15 sec.

ISO 200

f2.8 @ 1/1000 sec.
f4 @ 1/500 sec.
f5.6 @ 1/250 sec.
f8 @ 1/125 sec.
f11 @ 1/60 sec.
f16 @ 1/30 sec.

ISO 400

f2.8 @ 1/2000 sec.
f4 @ 1/1000 sec.
f5.6 @ 1/500 sec.
f8 @ 1/250 sec.
f11 @ 1/125 sec.
f16 @ 1/60 sec.

As you can see, the higher the ISO the faster the shutter speed at a given f-stop. As we "stop down" our aperture and admit less light, our shutter speed slows at any ISO. Why? Because at f2.8 all the available light is admitted. At f4, 1/2 as much light is admitted as at f2.8; f5.6 admits 1/2 as much light as f4; f8 admits 1/2 as much light as f5.6, etc.

Suppose we could assign a numeric value to the available light and our sunny day was a value of 10,000.

f2.8 = 10,000
f4 = 5,000
f5.6 = 2,500
f8 = 1,250
f11 = 625
f16 = 312.5

By looking at our examples we know that if stopping action is our goal then we need a higher ISO to keep our shutter speed high at any given f-stop. If we are shooting landscapes we can use a smaller f-stop since we aren't concerned with motion.

The aperture also controls what is called Depth of Field (DOF). However, the size of the sensor in digicams also plays a role in DOF, as does the focal length of your lens. You can find plenty of information on this with a simple google search.

Now lets look at some night time photography without flash. We now need a tripod since our shutter speeds are going to be very slow. Since your camera has a minimum shutter speed of 15 seconds we can use the camera's self-timer to release the shutter.

Suppose we want to take photos of the city skyline in the distance.

ISO 100

f2.8 @ 4 seconds
f4 @ 8 seconds
f5.6 @ 15 seconds

ISO 200

f2.8 @ 2 seconds
f4 @ 4 seconds
f5.6 @ 8 seconds
f8 @ 15 seconds

The examples for our night shoot are from my FotoSharp (fotosharp.com) Day & Night Exposure Guide. IMO its well worth having.

Expo Imaging (expoimaging.com) is a company that offers a DOF table (ExpoAperture2) that is useable with your camera. It accounts for sensor size and focal lengths to help you determine DOF. You can read a review of it at shutterbug.com - just type expoaperture2 in the Search box.


I realize this has been a lengthy answer. Hope it has helped.

Answer 2

The aperture is the size of the opening inside the lens that allows light to get to the sensor. Along with the shutter speed and sensor ISO it controls the exposure. The lower the number, the larger the aperture, so with less light the aperture setting should be a lower numbered setting.

The aperture also has an effect on depth of field, which is how much of the picture appears to be in focus. If you've seen a portrait with the subject in sharp focus and the background is all blurry, that was most likely done with a long lens and a wide open aperture.

Answer 3

Ok, firstly, the aperture is more or less the hole in the back of the lens. The bigger it is, the more light it lets in. Now, the fun part of it is, the bigger it is, the shallower your depth of field is. Which means the bigger you make the aperture (smaller number) less and less of the picture will be in focus.

I have the Canon Powershot A550, but I haven't really touched it (I bought it to disassemble it) so I couldn't tell you what it can and can't do.

Answer 4

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