What you are seeing here is the optical image of the physical aperture (called Virtual Aperture) seen through the front lens element. The Relative aperture (f-ratio or f-stop): the quotient of the focal length and the virtual aperture.The Virtual aperture (also called entrance pupil): the optical image of the physical aperture seen through the front element of the lens.To be more precise, aperture refers to three distinctive terms:

In the introduction, I referred to it asВ a hole inside of ourВ lens. We have three lenses with different focal lengths but almostВ identicalВ angles of view on their respective formats:ДЇirst letвЂ™s look atВ the aperture. LetвЂ™s get out of the way what has already been explained many times. The question is: is it correct to compare lens apertures between camera systems by considering just the depth of field? LetвЂ™s lookВ into this a little more. The easiest way to do this is to compare equivalent f-numbers. They are also interested in the overall look and shallow depth of field a fast lens can deliver.В Therefore itВ has become common practice to compare depth of field between lenses designed for different sensor sizes to get a clearer picture of how your image willВ look when taken withВ a smaller sensor. Photographers are interested in knowing how sharp aВ lens is wide open, how beautiful the bokeh (quality of the out-of-focus area) can be and how capable the lens is atВ isolating a subject. Shallow depth of field is popular for portraits, among other things. ItвЂ™s not just a technical aspect but also an artistic/creative element. A smaller aperture likeВ f/11 will produce a deeper depth of field so the distance will be longer and more areas will be in focus.Дepth of fieldВ matters because it can play an important role inВ the look/style you want to achieve. A fast aperture like f/1.4 will produce a shallow depth of field so that distance will be shorter and your image will have more out-of-focus areas. In other words, it is the areaВ that appears sharp (in focus) in the photograph. Aperture and Depth of FieldДepth of fieldВ refers toВ the distance between the nearest and farthest points from the focal plane that appearВ in focus. Why? Because thisВ is usually what matters to people when it comes to comparing camera systems. Take note of the first pointВ (the amount of light) and save it somewhere because I want to talk about depth of field first. This aperture affects two things: the amount of light that hits the sensor when you take the picture and the depth of field of your image. Smaller aperture (also referred as вЂњslowвЂќ)

Aperture 3.5 depth of field