How to control the depth of field in film photography?

Aperture "The larger the aperture, the shallower the depth of field". Photographers use a large aperture to obtain a shallow depth of field and blur the foreground and background to highlight the theme. It should be noted that the focus must be accurate on the subject, that is, the face of the subject. Subject Proportion The greater the proportion of the subject "person" in the whole picture, the shallower the depth of field, the more blurred the background and the more concise and powerful. A lens with a long focal length has a smaller viewing angle and a smaller background range. But more importantly, "a strong sense of oppression has caused a shallow depth of field." I often use this function when taking full-length photos, using 200mm or 300mm, but the disadvantage is that it is far from the subject. This trick often confuses the model, and then the author himself is tired to death (because he has to run around when shooting). Finally, I must remind you that you must focus accurately when shooting portraits in shallow depth of field. The most accurate way I usually take pictures is to focus my eyes, pay attention to the camera's focus prompt, whether it's a focus indicator or a buzzer, and then press the shutter after confirmation. After reading the above discussion about depth of field, do you have a deeper understanding of the relationship between "depth of field" and the equipment and shooting skills at hand? Controlling depth of field is a very important and necessary skill in photography. Students should practice more and take more photos.