Aperture

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universalady

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OK, so I understand alot more about the different shooting modes on my 550D after reading the manual & lots of playing around and taking lots of pics. And tbh, I usually shoot in Shutter Priority or Manual. BUT, I struggle with understanding how to use the Aperture mode. I have been reading up lots of 'guides' online, but actually using it and understanding it is a different matter.

I am one of those people that learns much better by using. What I am confused about is how long the shutter stays open when I take a picture, and how I can use the Aperture mode with a quick shutter speed. I understand that the lower the number, the more light will be let in, but even so, sometimes the shutter stays open for ages, meaning that the picture is horrendously blurred and often over exposed
 
If you put your Aperture at the lowest number the shutter speed will be the maximum you will get (all other factors being same, ISO etc,.)
- If you select a shutter speed of 1/500 your camera will meet that by lowering Aperture and/or raising ISO to get correct exposure.
- If you select Aperture F3.5 the camera will select the shutter and ISO to give correct exposure. This may or may not be faster or slower than 1/500.
You will see shutter speed change as you lower the Aperture so you should be able to get to the same shutter speed either way.
 
universalady said:
I am one of those people that learns much better by using. What I am confused about is how long the shutter stays open when I take a picture, and how I can use the Aperture mode with a quick shutter speed. I understand that the lower the number, the more light will be let in, but even so, sometimes the shutter stays open for ages, meaning that the picture is horrendously blurred and often over exposed
Click to expand...

You're on exactly the right lines. Bigger apperture (smaller f-number) means more light comes in so shutter speed will be higher.

Bear in mind that sometimes there isn't a lot of light to work with so even though you're getting the shutter speed as quick as possible, it might still not be quick enough for a steady shot. At this point you raise the iso which effectively amplifies the light and so you can use a faster shutter speed. If there is just not enough light you sometimes you just run out of options and need either a tripod or a flash.

Over exposure is harder to explain but maybe exposure compensation was dialled in or perhaps the scene was confusing the meter, a scene with a lot of dark/black tones can do this.
 
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Shutter and aperture, in conjunction to ISO control the exposure of your images (they are often refered to as the exposure triangle).

For instance, with the ISO set at 100, 1/500 f8.0 would give you the same exposure (roughly) as 1/250 f5.6. This is because the aperture is bigger so the shutter doesn't need to be open for as long to let enought light in to expose the shot correctly.

Using the same example of ISO100, 1/500 f8.0, by upping the ISO to 200 you could either change the shutter to 1/250 or the aperture to f5.6.

It would depend on the sort of shot you're taking and in what circumstances. For a landscape shot you may want a large depth of field so you would use a f8.0 - f16 so to compensate for less light being let through the aperture you would have to either use a slower shutter speed or increase the ISO or perhaps even a combination of the two.

If you need to freeze fast moving action with a fast shutter speed you could use a bigger aperture and/or increase the ISO.

So in terms of using Aperture mode...... You set the aperture depending on the depth of field you require OR control the amount of light you want to hit the sensor.

If you're getting blurry shots using Av mode, the chances are that the value you're chosing means the shutter needs to be open for longer to get correct exposure so you need to use a lower f-stop and/or increase the ISO.

If you post up one of your shots with the EXIF data intact we would probably be able to give you more specific help :)
 
Aperture Priority does exactly what Shutter Priority does but in reverse, so you set the Aperture you want and the camera sets the shutter speed, instead of you setting the shutter speed and the camera setting the aperture.

Depending on which mode you select, the controlling factors will be light and the lens you are using.

So f5.6 lens won't let as much light in as an f2.8 lens, therefore it takes longer to capture the image, so the shutter speed will be slower. You can influence this but changing the ISO settings, the higher the ISO setting 400/800/1600 etc the more sensitive the sensor is to light and therefore speeding up you shutter speed.

So shutter speed is influenced by the lens you are using, the actual aperture you are setting, the light conditions in which you are taking the photo and what ISO setting you have set.

The larger the aperture f-stop the more time the camera need the shutter to be open to take the image.

The aperture also influences the depth of field and sharpness of the image. Small f-stops f2.8/f2 have shallow depths of field (percentage of the image in focus), larger f-stops f9/11 etc have more depth of field and increase sharpness, but the images takes longer to capture because the shutter is staying open longer.

depth of field, think of a wall with birds sitting one behind the other. A shallow depth of field causes the 1st bird to be within focus and the other out of focus, as you make the f number bigger, the aperture actually gets small within the camera, you increase the depth of field thus increaseing the number of birds in focus to a point, and depends on the lens you are using

In manual you have complete control, how ever it does all depend what conditions (light) you are taking the photo in, sunny, overcast, raining, indoors, sunsets, sunrises etc
 
Try putting the camera in <gulp> 'P' mode, then spin the top dial, keeping an eye on the settings. You'll see that as the aperture increases, the shutter speeds up, and vice versa. That means that the same amount of light will hit the sensor regardless of the setting. At some point you'll run out of aperture or the shutter speed will drop to below hand-holdable.

This relationship is the very basis of correctly exposing your shots. Get the hang of this, and also how changing the ISO means one or both of the others will have to change, and how these relate to what the meter is showing, and you've cracked the fundamentals of photography. :)
 
gad-westy said:
You're on exactly the right lines. Bigger apperture (smaller f-number) means more light comes in so shutter speed will be lower.
Click to expand...

Wrong!

Wide aperture (small F no) means more light in, it also affects the depth of field - wide aperture, small depth of field (so blurring out area of background, for example). In reasonable light, a wide aperture will UP the shutter speed to enable a good exposure. In poor light, a wide aperture does not always guarantee a shutter speed fast enough to avoid camera shake so you need to choose an ISO as high as you need to obtain the right shutter speed.

Its the ISO/Shutter Speed/Aperture triangle.

My advice is set up a shot (say a pot plant on a table in the garden) and take a variety of shots at different apertures to see the effect.

Using P mode just 'hides' this technical stuff and allows the camera to do the thinking for you :)
 
Photodiva said:
Wrong!
Click to expand...

How charming.

If you read the rest of my post, it's pretty obvious that it's typo, I meant to type shutter duration rather than speed but hey ho, full marks to you.

I'll go back and edit to avoid confusing the OP.
 
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99% of the time i shoot A/P.

Knowing the DOF,i want in the photo,i adjust the aperture to give me that.

Then i do a quick check at what shutter speed the camera giving,to make sure i can get away with handholding or any movement.

If the the shutter speed seem to be getting to slow,i will push up the iso,as much as i can :)
 
As someone who is just starting out I find this thread very interesting and informative,

Written in terms I can understand.

Thanks
 
WOW, thanks to everyone who's posted, makes a bit more sense to me now :) I'll go away, and have a practice and see if I can understand it more
 
gad-westy said:
How charming.

If you read the rest of my post, it's pretty obvious that it's typo, I meant to type shutter duration rather than speed but hey ho, full marks to you.

I'll go back and edit to avoid confusing the OP.
Click to expand...

You're welcome :)
I think the word 'lower' is confusing whether you meant shutter speed or duration. Faster would be better.
 
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