Aperture priority mode

[Goldcoin79]

If you were shooting in aperture priority mode when would you chose to set a mid range aperture setting? I understand about depth of field so can see why you would open the aperture (low f number) up for a shallow dof if you want to take a portrait picture and blur out background and I also understand why you would close the aperture (high f number) for a large dof to take a scenic picture where you want it all in focus so when would you chose a mid range aperture setting?

James

 

[Espike]

I use mid range apertures for maximum sharpness. Using a really small aperture can cause diffraction. Check this out: Diffraction Limited Photography: Pixel Size, Aperture and Airy Disks

 

[pgriz]

With aperture control, you are balancing three things: quality of image, depth-of-field (DOF) and related to DOF, the amount of foreground and background blur.

As mentioned earlier, many lenses are sharpest at the middle of the aperture range. At the lower end of the aperture range, especially for lower-cost lenses, there are more optical abberations that show up. At the higher aperture range (depending on the lens and the format, but usually above f/11) diffraction effects increasingly blur the fine detail.


The amount of DOF you need for a given image depends on what you are trying to achieve. Wide-open apertures (f/2.8 and below) usually give you a very thin DOF, which in the hands of a capable photographer will give a sharp focus on the element of interest, but blur any distracting foreground or background object. If this isolation is NOT desired, as in, for instance, a scenic shot, then you need to choose an aperture which will give you enough DOF to cover the entire range of interest.


Keep in mind that DOF is also affected by the focal length of the lens, so that f/11 at 14mm will be essentially hyperfocal from about 2 feet to infinity, while at 200mm and focused at 10 ft., you will have a DOF of about 4 inches.

 

[KenC]

There are times when you need some DOF, but not a lot, e.g., when photographing a relatively flat area, so intermediate settings are enough and they allow a faster shutter speed or lower ISO than a really high aperture number.

 

[Dao]

Also there are times you really do not care about DoF and light is not an issue, then I will choose the aperture around f/8 or whatever the lens' sweet spot is. (i.e. subject is far away in which there are not much of a difference as far as DoF concern when shoot with f/4 or f/11)