aperture and depth of field explained

Aperture and depth of field explained

as a result of another online query from one of our subscribers, In this article I am going to explain how the aperture and depth of field are connected. This will be an optical explanation and it is addressed to people with a bit of understanding of optics. As I have discovered there are among our readers technical savvy who can understand and appreciate this information

before getting deeper into the technical explanation, I would like to point the previous tutorials that will support this info

Understanding light in photography

Depth of Field tutorial

Let’s remember few things:

– light comes from a light source as photons and waves, bounces on our subject and camera captures the bounced light which goes through the lens onto the sensor

– light changes direction when it changes the material it goes through, such as air and glass in our case but it applies to all transparent materials, like water, petrol, diamond and so on.

– the spherical shape of a lens can make the photons converge to a single point. If the curvatures of the lens are not perfect, the light convergence will not happen.

– every lens or combinations or lenses are acting as one

– for each point in front of the lens there is a correspondent converging point beyond the lens. Depending on the distance between the sensor, lens, and the subject, we have only one situation when all the light from one single point turn into another single point on the sensor. Only in this instance we have achieved perfect focus. If this relationship is not right, and the point of convergence is in front or beyond the sensor, when for one point in the image, we have an area projected on the sensor. This means out of focus or a blurry result.

– for each instance there is one continuous distance from the camera which is the focus plane, in reality it is a focus sphere. all points situated closer or further than this virtual sphere will not have single points corresponding on the sensor but spots which are over one another and this is the out of focus blurry effect. It is a reality than the focus sphere has a depth in which the human eye cannot perceive small differences and it is acceptable as a reasonable sharpness. This is the depth of field, or the depth of the focus sphere.

– aperture is limiting the light cone in the relationship described above which sometimes decreases the size of the areas corresponding to a single point in the scene. The purpose of this is to bring more space into the acceptable depth of field, or let;s just say making focus sphere deeper, so more objects appear in focus, and decreasing the blurriness overall.

So this is the relationship between the aperture size and the depth of field. the smaller the hole,  the sharper the image will be. If you do not have a perfect natural vision, and you are trying to look through the tiny holes created with your hands, you will notice that the images are sharper, regardless of the glasses your are wearing. of course the image is going to be darker, as you limit the amount of light going through, and that applies to camera sensors as well which limits the exposure level and requires longer exposure times, and that is the other exposure triangle element, the shutter speed but that is not what we are talking about here


I hope I have shoed very clearly how the aperture and depth of field are interconnected and what will help you understand easier the basic exposure.

If you have any questions, please leave your comments done below

thank you




About Christian Tudor

professional photographer, main editor at Academy of Photography and owner and principal photographer of Tudor Photography