What's the point of a DOF calculator?

I legitimately have never ever found a practical use for one yet. Could someone please explain?

Like, I kind of figure if I'm at 24mm at f/16 (focused at infinity), and what I'm trying to shoot is like 5 feet away, then anything within a couple of feet of me will be out of focus, and anything past that will be in focus. Is that basically all it does? Figure out that math for me?

It tells you for a given focal length, f-stop and subject distance what is your depth of view, where it starts to get in focus and where does it stop.

See here:
http://www.dofmaster.c​om/dofjs.html

In my opinion, depth of field (DOF) calculators such as this very popular one are very useful as training aids but are less useful in real life situations. The reason for this opinion is simple.

DOF calculations are based on a set of rather arbitrarily chosen variables. For example, they are written assuming that all images being analyzed for DOF will be viewed at one specific image size and will be viewed from a specific distance. Furthermore, there are assumptions made on the visual acuity of the person making the analysis of what's "in focus" vs what's "out of focus". The fact is that most folks view their images at sizes and distances that are different from the DOF calculation design variables. Thus, the DOF is actually different in those images than what the calculator output suggests.

DOF calculators allow the photographer to play with variables such as focal length, camera-to-subject distance, and aperture settings and see the effects on depth of field. This is great for training as long as the photographer understands what the paragraph above is all about.

I do a lot of candid people pictures without a flash. Very often I use a prime 50 or 35 mm / 1.4f lens and fairly fast shutter times.

I use the DOF calculators ahead of the shoot to get an idea for the minimal aperture I should use in different situations - and under which situations I need to lower the shutter times. E.g. the minimal f-stop I need for a group of 3 people with either the 35 mm and the 50 mm....

And yes, by now I should know that by heart - but I still now and then use the DOF calculators to refresh my memory.

kjonnnn wrote in post #16510937
But, using your example, suppose you're not at f16, youre in low light and have use f2.8 at 10 feet from a group. How many will be in focus? What if you're using an 85mm at 2.0 on a headshot for someone. what's your DOF then? its not feet ... Its inches. If you're shooting everything with a wide angie at f16, you may not see the purpose of it. But most people shoot with a variety of lenses at a variety of distances and focal lengths therefore making DOF not always easily identifiable.

Yes, you are quite right, but it is only really useful as a vague learning tool to get a rough idea of DOF distances. To play with apertures, focal lengths and distances and go "ooh, thats not much, I'd better remember to stop down in that sitiuation".

When actually taking pictures in the real world, you are guessing at the distance to the subject, how far apart the group may actually be etc., so you don't have accurate starting numbers, do you know how big the final image is going to be, or might you want to make a big print out of it, which buggers up the numbers even more, is the "acceptable" sharpness that is used for the table acceptable to you?

Sure, for a newbie, it can be useful to have looked at a dof table and got a rough feel for how shallow dof can be with long lenses at short range, wide open etc. But once you start using the camera, you very quickly learn from experience and can just look at the subject, and the approximate distance, and then pick a suitable aperture.

In the field, dof tables are pretty useless unless you are going to measure everything then enter the exact figures in. If you are just using a rough estimate, then the dof preview button on the camera will give as good an idea as any dof table, and just takes a second to use.

I have been a photographer for over 35 years and the only time I have ever used a dof table has been on these forums when answering cries for help and wanting to be able to say "well, at that aperture and focal length you only have xxx dof at xx feet" as part of my reply. I have never found any practical use for them in actual photography.

They use such precise numbers, to hundreds or even thousands of an inch, that people think they are an exact science but they are actually a very vague and fuzzy concept, and dof varies so much with variables that the tables don't account for (unless using fancy ones where you can input print size, viewing distance, visual acuity, CoC size etc) that they are only ever a very rough guide.

It's interesting, from the comments here it looks like some folks find them useful. For the photography I do, the settings are pretty much "rule of thumb". Yeah, I've gone over the DOF charts/calculations, and it's given me a "rough view" for that rule of thumb to work, but then out in the field I've never needed to resort to one...

Short answer - DOF calculator is the same as DOF scale.

If you are AF dependent, you don't need DOF scale. Or if you like to take pictures with fisheye.
Or if you are with MF SLR and limiting yourself to central spot focusing, it is OK without DOF calculations.
Then I was taking landscapes digitally, DOF was helpful to determine what is going to be in sharp with 70-200 lens.
Then I was taking street pictures with 5D and 50 1.4 ZE knowing of DOF was the ticket to take pictures within couple of seconds, at large apertures and in busy areas. You would have to walk like Erik Kim if you want to use AF for shots like these.

Now with my Medium Format very old film cameras and new lomography gear DOF is the only solution and DOF calculator helps a lot, at beginning.

Beyond playing with them for an afternoon to help get a better understanding I will only touch a depth of field chart or calculator if I'm trying to plan something out and work out details ahead of time. Such as when on the bus heading over for some event and I know I'll be doing a few preplanned shots, then I will break out the sketch pad and smart phone to crunch numbers to get preset ranges. When I get there my camera and flashes are already set within the ballpark, and I just have to pull out the tape measure and a bit of masking tape to lay stuff out.

Fudge factor adjustments are a short breeze, and I've gotten to kill boring time sitting in a vehicle I'm not driving.

DoF calculators are great tools for explaining why somebody's shots are out of focus, or why you don't need to shoot at f22 when using a 10mm lens and similar situations. People will believe an online DoF calculator when they would refuse to believe a human being telling them the same thing.

Literally the only reason I shoot f/22 is to have a longer exposure time.

quadwing wrote in post #16512800
Literally the only reason I shoot f/22 is to have a longer exposure time.

But surely from whats been said here, you now understand that the DoF is very different as you use the different apertures?

Maybe f/22 is a little extreme, but f/8 to f/16 is fairly normal for landscape shots.

quadwing wrote in post #16512800
Literally the only reason I shoot f/22 is to have a longer exposure time.

So, you are the Original Poster...do you have a question?

quadwing wrote in post #16512800
Literally the only reason I shoot f/22 is to have a longer exposure time.

What about the times when you are using a longer focal length, say, like the long end of your 70-300mm, when you have something just a couple feet away that you want to be sharp and in focus, but also want the things in the background to be sharp and in focus? For all of these situations, do you find that f16 is sufficient? I actually use f32 on occasion, when I am using long glass and want a lot of depth of field, because I find that f22 often isn't enough.

quadwing wrote in post #16510404
I legitimately have never ever found a practical use for one yet. Could someone please explain?

Like, I kind of figure if I'm at 24mm at f/16 (focused at infinity), and what I'm trying to shoot is like 5 feet away, then anything within a couple of feet of me will be out of focus, and anything past that will be in focus. Is that basically all it does? Figure out that math for me?

In the old days, every lens had a built-in depth of field calculator. This is one reason why I use the Fuji X-E1 with a Speedbooster; I can rapidly identify maximum depth of field for any aperture setting with my Canon FD lenses.

They're handy for calculating really tiny DOF when using a macro and focus stacking. Your DOF could be 0.3mm or so. If you want a complete set of images to stack to achieve a deep macro image, you need to know how much to adjust your rail.

Otherwise, like folks here have said, I don't use them for anything else.