![]() Now IF you move the subject closer to the camera, the DOF decreases as you approach the camera, that is why the dof is the same for a wide angle lens and a telephoto IF the subject size is held constant. The depth of field is a function of the distance to the subject plane and the aperture, focal length is a minor consideration.įocal length really has a minimal effect on DOF - IF - the subject is held to a constant size on the sensor. The data in the DOF calcculators is directly from an optical formula. I realize this is not scientific but it makes sense to me! I would like to hear if folks agree with this basic assessment/methodology.though of course we may diasgree on the numbers a bit :ivarĪlso the one thing that has been bothering me.the data on the DOF calculators.how is that determined? How do they know what is in focus and what is not? It seems every lens would be different to some extent according to the design of the optics. Note my wife is short! The calculus will change a bit for wilt chamberlain!:wink Assuming you hit the right spot focal point. This kind of analysis allows you to to set an fstop and fire away at heads or torso knowing you are going to be in full focus and not miss a nose or ear, etc. This translate roughly to 1 full fstop between the calculated and "acceptable" f stop.ġ) head shot at calculated fstop is 13.5 but you can get away with say 9.5.Ģ) torso shot at calculated fstop is 4.8 but you can get away with say 3.5.ģ) full length shot, you can use any fstop! Note that an f stop of 2 will give you a DOF of 0.77 in which is quite close to the 0.78 in of "acceptable DOF". So what does that mean? It appears (at least in my eye) that the "acceptable" DOF is actually larger then the DOF you get from the calculator by quite a bit. Now what does the DOF calculator say? at 85mm and 1.4 and 54 inches away, the official DOF = 0.54 inches. I have to multiply the 0.875 with 48/54 to get the DOF on the plane of the camera/lens. The tape measure is on the 48 in leg but the DOF of the lens and camera is centered on the 54 in leg. The triangle that I formed is right triangle with the hypotenuse of 54 in and legs 48 in and 25 in. Now to compensate for the fact that I am shooting at an angle to the tape measure, *busts out 9th grade geometry book*. This translates to 7/8 of an inch or 0.875 inches on the TAPE. My eye tells me that the focus is reasonable from 12 inche mark to about 12 and 7/8 mark. I know everyone will have different opinion on this and it depends on different factors. Now you can measure what you judge to be "acceptable" focus. Note the min focusing distance of the lens is round 3 feet. I laid a measuring tape out on a table and took a photo of it with single site focus on the 85mm lens at 1.4 and 54 inches away centered closely to the 12 in mark on the tape. Then I began thinking, well what does the DOF really mean? Perhaps it is technically what is in perfect focus.but what about what is "acceptable" focus. Really? I can only use my lens wide open on a person from 16 feet away? I swear I was getting in focus shots with a lot lower f stops.įor the waist up shot at 8 feet I assumed a 6 in DOF is needed and that calculated to a min fstop of f/4.8įor the head to ankle shot at 16 feet I assumed 8 in of DOF is needed and that calculated to a min f stop of f/1.4. Using DOF calculator you need to be at f/13.5 to achieve this! That seemed rather high to me. I assumed for the tight head shot you need say 4 inches of DOF if focused on her eyes to get the the face, ears, hair, in focus. So what f stop should I use to get everything in focus for each of these types of portraits? I had been choosing say 2.8 for a head shot previously.was this justified? 1st I made these assumptions which may use some tweaking. Then I moved back further to get an almost complete head to ankle shot: I looked down at my tape measure and noted I was about 4 feet give or take few inches. I then got to proper distance for tight a head shot. So I brought out my tape measure and laid it on the floor and had my wife stand against the door. My finding were a bit surprising to me so i thought I would share. I have the nikkor 85mm 1.4 and am trying to get a more natural feel for what I should be setting my aperture at to get a portrait in focus. I have been on a depth of field study recently.
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