What is the difference between aperture priority and using the focus ring on the lens?

Question

Adjusting your aperture allows you to obtain the depth of field that you want. What difference does it make if you just use the focus ring on your lens to get the same result?

Answer 1

Aperture priority and the focusing ring are not related. The focusing ring on the lens focuses the image. Aperture priority allows the user to shoot at a fixed f/stop. Using aperture priority allows you to shoot all of the images at the same f/stop which will result in the shots having the same depth of field provided that the focal length and focusing distance is constant.

Answer 2

I think that terms are being confused here everywhere. You guys are referring to two totally different things.



1- You are asking about difference between 'focus ring' and Aperture priority.

2-sant kabir is referring to OLD lenses that had also an aperture ring on the lens (besides the focusing ring)



Now. Focus ring has absolutely nothing to do with Aperture priority and, in general, you can not use one to substitute the other.



Focus ring simply "decides" where the focus is at any time. The aperture used decides "how much" is in focus in front and behind of the focus point.



The only time that focusing sort of resembles the functions of the aperture is when you want to have a large depth of field and want to use a small f number (large aperture) BUT you have to take many photos, stack them all together and blend them without ever touching the focusing ring but only but moving the camera in the proper axis (Very used in macro photography). If you don't do it that way, you won't be able to properly blend the images.



If you have more questions or still don't understand very well, let me know and I will give you a hand.



Again, to summarize:



Aperture decides depth of field.

Focus ring decides where the focus is set (no matter what the depth of field)



Edit #1: Ok, seeing your example. It seems there is still a bit of confusion but we are getting there.

Let's use the example of your flower. Flower is there, you get pretty close to the flower and you use the smallest f-stop number (that is the biggest aperture of your lens) then you use the focus ring to focus on a certain spot of the flower. It is most likely that except for what you are focusing on, the rest of the flower will be out of focus and blurred. For a close-up photo of a flower where you want everything out of focus, except for the flower itself, you either use the method I mentioned earlier or get the flower very well separated from the background and chose a proper focal distance/aperture combination to guarantee that the flower and nothing but the flower is in focus.

The reason why you can not use them interchangeably is: Say your aperture is on X and your focus is on distance Y but there is nothing at that distance, then everything is out of focus. Now, let's say that something is at that distance Y, then whatever is that that distance is in focus a certain amount in front of and behind Y and that will be given by the X you selected.

In other words. If you don't focus, you will never accomplish focus using Aperture priority. (This is a bold statement since having a wide angle lens on a large f-number will guarantee that almost everything is in focus in your photos).

The nature of Aperture and Focusing is optically different. And that's why you cannot use them to substitute the other but to complement each other. Aperture uses the diffraction/or not of light while focusing refers to ray of lights that actually converge



Pfff... I feel like I wrote an essay here! Again, if you have more questions... you know...



Check the extra link I added... It will show you examples.



For more info, check these links, they will help you understand:

Answer 3

I seem to understand what you're asking, although I can't put it into words. When you focus you establish a distance where your subject (area) is located that serves to capture crisp details. However, the aperture you use will affect and determine the area in back and in front of the subject that appears in focus (depth of filed).



You will discover that focusing is one element that you need to capture an image; it is an important element but NOT the only element you must take into consideration (aside from composition, light, etc).



IF you want an out of focus background, then you can use a a wide aperture so the shutter will open and close quicker, not giving the background reflected light time to reach the camera lens; or you can use longer focal length to achieve a similar effect. However, to increase background detail and increase the area within depth of field, you would have to use a smaller aperture that will likewise, affect the shutter speed, but this time to be open longer, to give the reflected light from the background time to reach the lens to capture less fuzziness but more details, hence more focus.



You would think using slower shutter speeds is better, huh? Not really. Slower shutter speeds will allow for motion blur by the subjects or even by the person holding the camera (camera motion blur) unless the camera is mounted on a tripod, while a faster shutter speed can freeze action. There are times when a bit of motion blur is purposefully used to show action. But, not always; that comes with experience and knowledge.



But, wait a minute. There's still yet another element you must contend with it. ISO. HOW sensitive the film or sensor is to light. The less sensitive, as noted by lower numbers, as opposed to more sensitive, as noted by higher numbers. The more sensitive, the faster the shutter speeds will be and slower with higher numbers and the size of the aperture will likewise be affected accordingly.



Good luck and have fun.

Answer 4

Let's say there's a platoon of soldiers in formation in front of you. You focus on the soldier at the center. Focus is on the subject to make it clear.



If you want that soldier to be the only one clear, you set DOF short so everyone else is blurred out. If you want a group photo so everyone in the picture is recognizable, you make DOF long so everyone is clear. DOF, the area around the subject (in focus) that remains relatively clear, not as clear as the subject but still clear enough, with clarity fading as you go farther from the subject.



Make no mistake, focus and DOF are two different things but are related. Aperture on the other hand is simply the size of the hole. It is not used for focusing but it is one factor that affects DOF, besides focal length and the distance of subject to camera.

Answer 5

We focus our camera to achieve “tack-sharp” focus at a specific distance. As an example we use the focus ring position the lens so that the camera is focused on an object 20 feet (6 meters) distant. Geometric optics tell us that tack-sharp focus is only achieved for this specific distance. In other words, objects 19 feet 11 inch and closer are out-of-focus as is objects 20 feet 1 inch and further. Now any one that has done even a little photography knows this is false. There exists, a span of distance before and after the distance focused upon that will be recorded by the camera as “acceptably in focus”. This zone is called depth-of-field.



You are asking about how we can control the span of depth-of-field. You need to know, for general picture taking situations, This span is not split down the middle, it extents about 2/3 further behind the point focused upon and about 1/3 back towards the camera. We use several available camera settings to control the length of this span. In some cases we want to set our camera to gain the maximum possible depth-of-field. Consider a landscape with everything in focus from just a few feet ahead of the camera including distant mountains. Some times when photographic a friends face, we want the eyes in sharp focus but we intentionally set the nose and ears slightly out of focus. In other words we use are acquired skills and control the span of depth-of-field.



How do we do this? We use the focus ring to set the distance. We set the lens aperture. Tiny working apertures like f/22 and f/16 deliver abundant depth-of-field. We use large apertures like f/5.6 or f/4 or f/2.8 to realize shallow depth-of-filed. We select the focal length of the lens to gain the desired depth-of-field. Short wide-angle lenses deliver a vast span of depth-of-field whereas long telephoto lenses deliver shallow depth-of-field. We use subject distance. Close focusing on nearby object delivers shallow depth-of-filed. Focusing on distant subjects grants enormous depth-of-filed.



In summation: You need to read your camera manual and study the fundamentals of the camera so you can master this and all the other aspects of your chosen hobby.

Answer 6

What? The focus adjustment has NO control over the depth of field, which is the RANGE of the area in focus. The focus on the lens allows you to focus on your subject. The aperture is controlling how much area in front of and behind the subject is in focus.



Ummm.... you seriously need to do a lot more studying about photography.