DSLRs have to modes to operate them:

• The classic viewfinder-approach: You set the aperture, shutter speed, and ISO value. The only ways to know if you exposed properly is either the exposure indicator - or to take a picture and find out by looking at the result. It is possible to see the change in depth of field with most cameras as they offer a preview-button that will tell the lens to close the aperture to the value you set.
• The LiveView-approach ^{(used by MILCs per default)}: What you see is what you get. To do that, the camera tries to change all parameters live.

And this is why you hear a clicking sound - it sets the aperture as soon as you change it.

DSLRs have two modes to operate them:

• The classic viewfinder-approach: You set the aperture, shutter speed, and ISO value. The only ways to know if you exposed properly is either the exposure meter - or to take a picture and find out by looking at the result. It is possible to preview the change in depth of field with most cameras as they offer a depth-of-field preview button that will tell the lens to close the aperture to the value you set.
• The LiveView-approach ^{(used by MILCs per default)}: What you see is what you get. To do that, the camera tries to change all parameters live.

And this is why you hear a clicking sound - it sets the aperture as soon as you change it.

DSLRs have to modes to operate them:

• The classic viewfinder-approach: You set the aperture, shutter speed, and ISO value. The only way to know if you exposed properly is the exposure indicator - or to take a picture. It is possible to see the change in depth of field with most cameras as they offer a preview-button.
• The LiveView-approach ^{(used by MILCs per default)}: What you see is what you get. To do that, the camera tries to change all parameters live.

And this is why you hear a clicking sound - it sets the aperture as soon as you change it.

DSLRs have to modes to operate them:

• The classic viewfinder-approach: You set the aperture, shutter speed, and ISO value. The only ways to know if you exposed properly is either the exposure indicator - or to take a picture and find out by looking at the result. It is possible to see the change in depth of field with most cameras as they offer a preview-button that will tell the lens to close the aperture to the value you set.
• The LiveView-approach ^{(used by MILCs per default)}: What you see is what you get. To do that, the camera tries to change all parameters live.

And this is why you hear a clicking sound - it sets the aperture as soon as you change it.