Aperture Blades


Today’s Question: What are “aperture blades?’  You talked about those in the context of sunburst shots [in the webinar on wide-angle photography].

Tim’s Quick Answer: The aperture blades are the individual components that are used to form a roughly circular shape for the lens aperture that allows light to pass through the lens to the image sensor (or film).

More Detail: An aperture is in theory a perfect circle through which the light passes from the lens to the image sensor. With many lenses, when the aperture is wide open the aperture blades are retracted to the point that the aperture is a true circle, with no impact from the aperture blades.

The issue is that the circle for the lens aperture needs to be at different sizes, based on the f-stop you’ve selected. So the circle would be small for f/22 and large for f/2.8, for example. But making a perfect circle that can be resized isn’t all that easy. So instead, the aperture is comprised of a series of “blades”.

These blades generally have an arc on the side that will form the outer edge of the circle for the aperture. A series of these blades are assembled in something of a circle, so the inner edge of each blade helps to form a portion of the circle. These blades can all be brought closer in to the center of the circle to form a small aperture, and further away to form a large aperture.

Of course, with multiple blades forming the circle, that circle won’t in fact be a perfect circle. There will be little “notches” where one blade overlaps with another. Those notches are what cause the sunburst effect to occur when the aperture is stopped down to a small size (such as at f/22).

For those who may have missed my webinar presentation on wide-angle photography, which included a discussion of how many blades are used to create the aperture for a given lens, you can view the recording on the Tim Grey TV channel on YouTube here: