You can't talk about DoF like it's the same as the focal plane. Alex, when I say Plane of Focus I am simply referring to an invisible plane that includes what is in focus. Depth of Field is by definition the distance between the Plane of Focus or the distance between the things that are in focus in that shot. Using them interchangeably is like using Meanline and X-Heigh interchangeably in graphic design - one is the thing the other is the distance to the thing but we'd understand the basic same function of them.
Consider also that when teaching Depth of Field you are teaching usually to someone that is very new to Photography, so I try to keep things and explain things in ways that are simpler to grasp initially.
Lance, that is exactly my issue here. This is just wrong way to teach such important concepts like DoF, especially to beginners. When beginners get confused by misconceptions like "cropfactor influencing DoF", "magnification influencing DoF", "DoF is a plane but with depth", "manipulation of objects in the frame could affect DoF" this assumed in you article etc. I strongly believe, it's one of the reasons of why there are so many people taking snapshots and sorry pretending they are art makers.
Fuzzy concepts create fuzzy images where even creator can't explain what are they about. Once you know what is going on with aperture, rest will be easy, obvious and clear of misconceptions. Do you guys know what is the circle of confusion? It's a bunch of photographers sitting at a round table and discussing DoF!
I agree that the essential step is understanding why aperture affects DoF - agree with you there, but I would also say its important to know that its not the only thing and the distance is a component. Its why my students are able to create shallow depth of field shots with their kit lenses at 5. DoF is affected by aperture, distance to an object you are focusing on, lens aberrations and resolution plus the output resolution billboard, gallery print, 6x4, web etc. The first two are related to the way lenses work and effect real DoF.
Rest of them control perceived DoF. What you describe above is perceived DoF. You can't change actual DoF of a 5. Nobody should mix actual DoF with DoF perception in a final print. This is one of major misconceptions.
Few more are in my post above. You can add to the list the idea that you can compensate DoF and focal length differences by getting closer to the subject. Ah, almost forgot. The hyperfocal distance. Who can explain what is going here? It's simple if you understand that the aperture controls the circle of confusion and that smaller object gets in a projection, sharper it LOOKS for a given focal length.
Look at the magnification formula I showed before. Shorter the focal length and further the object is, smaller it is in the projection. So for a wide angle lens, magnifications drops with distance faster than for a telephoto.
When you focus at a distance when further "edge" of DoF has relatively similar circle of confusion as the objects at that distance you see all of them as equally sharp.
Hence the hyperfocal focusing effect. This is again, perceived DoF not actual. You are using "Plane of focus" and DOF interchangeably and they are not. Plane of focus is an invisible plane that extends up and down and left and right from the "Point of Focus" any "Defocusing" that is at the edge of the "Width" DOF is Depth not width at the edge of the width is caused by Field Curvature of the lens not DOF As to your Debate. The plane of focus exists on the same plane as the sensor, how much information will be included in that plane is determined by the DOF - I would see an argument to say that the PoF is a plane that only includes critical focus and DOF is the distance from the front to back of acceptable focus.
But, I am really more referring to the idea of the invisible plane or invisible area that is in focus not so much the technical definition of PoF - introductory courses where this info would be taught require for me to explain things in ways someone new to these concepts would understand, the PoF term is not really a basic term, at least I don't think so. So when you say that the plane extends up and down and left to right, you are correct, it fills the viewfinder - agreed - the plane follows the plane of the sensor - I think yo are alluding to that as well.
I am then attempting to have readers visualize that as you change your aperture this plane gets wider from front to back to include more in the "Depth of Field" - the distance.
I fully understand that you want to keep it simple for beginners, that's my goal too which is why the terms you are using are confusing them. As you will have seen from the example above, larger apertures smaller f-stop numbers result in a shallower depth of field, where less is sharp, while smaller apertures higher f-stop numbers will result in a greater DoF, where more is sharp.
There are three different factors that influence DoF — aperture, distance from your subject and magnification.
In any of these modes, you can simply adjust your aperture using either the front or back control wheel of your camera. Interested in portrait photography? Click here. Changing the aperture is the easiest way to control depth of field. As we've already explained, larger apertures result in shallower depth of field while smaller apertures result in larger depth of field.
Although this may be the easiest way to adjust the depth of field, it is not the only way. The distance from your subject will also affect depth of field. The closer you are to the subject, the shallower your depth of field will be and vice versa. At the same aperture, shooting closer to your subject will give a much shallower depth of field, while shooting further away will give a much greater depth of field.
This is due to magnification, which we'll look at next. Magnification is the third factor that affects depth of field. The point spread function of an optics system is also called the impulse response. The resultant image is one which is the convolution of the target image and the point spread function. At least for non-coherent imaging. So the perception of the depth of field is linear with the f-stop and focal length.
Unfortunately, depth of field has it limits, and a very very small aperture will not provide nearly infinite depth of field, because diffraction plays a greater role, in blurring the image, as the aperture gets smaller.
So what really happens with depth of field is that objects are not really in focus off the focused plane, but rather the blur is considered negligible. Think of it this way: a thumbnail photo might look clear, but if expanded to be an 8x10" photo, it may be unacceptably fuzzy.
In practical application, a so-called hyper-focal setting on a lens, may give an acceptable image of a scene when viewed on a small format display or print, but when expended or enlarged, will yield a more fuzzy appearance as it is in reality not completely in focus through the "depth of field.
As a photographer and physicist myself, I am trying to explain this phenomenon to my musician friend who has just bought an expensive camera. The best I can come up with is to take, at the extreme, a pinhole camera with infinite depth of field.
As we stick a lens in front and widen the aperture it becomes closer to the familiar situation with object and image distance determined by focal length.
Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Why does changing the focal length negate the effects on DOF?
This is because the visual properties of a given lens either provide either greater DOF shorter lenses or shallower DOF longer lenses. The physical properties of a lens at a given focal length also affect the depth of field. The mm lens has a remarkably shallow depth of field. Manipulation of depth of field is a good way to modify the characteristics of your photo, and manipulating the aperture is the ideal way to do this because it has little or no effect on composition.
You simply need to change the shutter speed or change the light sensitivity — ISO to compensate for the changes in the exposure from the adjustments to the f-number.
Changes in distance and focal length also affect DOF, but these changes have trade-offs in terms of composition.
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