DOF question for you pros

I've begun my "apprenticeship" in the world of wedding photography under the tutelage of a good friend who owns a very successful studio in my area. I'm learning a ton each time I go out.
One thing I'm curious about though is having enough depth of field. I read a lot on this forum how many folks are shooting indoor ceremonies (and other less than ideal lit locales) at f/2.8 using some pretty nice glass (17-55 f/2.8, 24-70 f/2.8 & 70-200 f/2.8). At some of those longer focal lengths with apertures of f/2.8, the depth of field is crazy shallow; how do you keep enough of your subject in focus? Obviously by my signature I don't own any of these fine lenses, but eventually when I can justify it, I'll be improving my lens lineup and this is one area I'm kinda fuzzy on.
Thanks for any insight you can offer.

Stand a bit further from the subject, then crop in post.

It's fairly the norm to use shallow DOF whilst shooting weddings. Why? For a couple of reasons. Firstly it can give an appealling background blur (bokeh) when needed but also because we are quite often working with limited light and have no other choice. Apertures such as 2.8 should not be shyed away from. However there takes a certain amount of skill to use it effectively. 2.8 or less is fine esp when photographing one person, as long as their eyes are the point of focus the photo usually works. This has been demonstrated wonderfully in a recent post here on POTN where the photographer was using 1.2 for some of these photos. Notice perfect focus on the eyes whilst much of the rest is not.
https://photography-on-the.net …/showthread.php​?t=1045192

I certainly wouldn't use 2.8 when photographing a group of people, eg a family group. The people in the front may be in focus but the fella 1 metre behind wont. I usually opt for about f 4 - 5 range in situations such as this.

I also question wedding photographers who shoot the entire wedding at f1.4...esp with Canon bodies (lol) 'cuz I certainly couldn't do it and have an acceptable number of keepers.

So here's how I do it: I have one body that gets the "safe" shots. It has a 24-105 f4 lens on it, and I nearly always use a flash, and a second body with the exotic wide open stuff. I make sure to get a shot or two with the safe body before switching to the "artsy" body. So, for example. during the first dance, i will shoot a dozen [photos with the safe body, then switch to the body with the 85 f1.2 to see if I can get one or two in focus. When I do, it is magic. If I don't, then I still have the safe shots.

For the portraits, I quite often shoot at wider apertures. I just explain to the couple what I am doing, and ask them to imagine that there is an invisible plane of glass in front of them. That usually puts them both in the focus zone.

On full frame, F2.8 70mm standing 3m from the subject, dof is 30cm. At 30mm/3m it's 2m dof, at 200mm at 6m it's 7cm. With that it's easy to keep the subjects in focus.

http://www.dofmaster.c​om/dofjs.html

There's an app for that!
At least there is one for Android phones. DOF Calculator will calculate the depth of field. Check it out.

We used it to see what we would have with a 500 mm lens mounted on a 7D at 200 feet. (Aimed at home plate from beyond the outfield fence at a softball game).

MT Stringer wrote in post #12513117
There's an app for that!
At least there is one for Android phones. DOF Calculator will calculate the depth of field. Check it out.

We used it to see what we would have with a 500 mm lens mounted on a 7D at 200 feet. (Aimed at home plate from beyond the outfield fence at a softball game).

Just can't get into all this kind've gadgetry or maths, esp whilst photographing a wedding which to me is more of a creative venture than a technical one. All I need to know is that the likes of 2.8 will yield a shallow DOF and is applicable for many situations, and I've learnt from experience and mistakes.

highway0691 wrote in post #12513168
Just can't get into all this kind've gadgetry or maths, esp whilst photographing a wedding which to me is more of a creative venture than a technical one. All I need to know is that the likes of 2.8 will yield a shallow DOF and is applicable for many situations, and I've learnt from experience and mistakes.

Yeah, I learned all of that stuff back in the 70's. So what do you think the DOF is at 200 feet, 500 f/4, Canon 7D?

Note: The ball game is an action event, similar to a wedding. Only once the lens is aimed and focus set. The remote will do the rest.

MT Stringer wrote in post #12513582
Yeah, I learned all of that stuff back in the 70's. So what do you think the DOF is at 200 feet, 500 f/4, Canon 7D?

Note: The ball game is an action event, similar to a wedding. Only once the lens is aimed and focus set. The remote will do the rest.

Wouldn't have a clue actually. Shooting a moving subject at 500mm from 200ft, then this knowledge would be important to a sports photographer.

My subjects during a wedding are moving slowly, and sometimes not at all. And Theyre usually only 2 - 5 metres away and shot anywhere between 28 - 200mm, so we're not talking the same ball game I suppose.

DOF is related to aperture and size of subject filling the frame.
You do not need to know the distance or the focal length.
(for any portrait size subjects)

How to estimate DOF without focal length or distance
https://photography-on-the.net …/showthread.php​?t=1030942

Focal length affects the appearance of the OOF image.

CaptivatedByBeauty wrote in post #12514167
DOF is related to aperture and size of subject filling the frame.
You do not need to know the distance or the focal length.
(for any portrait size subjects)

How to estimate DOF without focal length or distance
https://photography-on-the.net …/showthread.php​?t=1030942

Focal length affects the appearance of the OOF image.

Your "size of subject in the frame" is an informal way of saying the lens length and distance to subject. You need to quantify things to make calculations.

All DOF calculators i've used take distance to subject as a parameter. They wouldn't take it if they didn't need to.

tim wrote in post #12514485
Your "size of subject in the frame" is an informal way of saying the lens length and distance to subject. You need to quantify things to make calculations.

All DOF calculators i've used take distance to subject as a parameter. They wouldn't take it if they didn't need to.

Nope, it's not informal, it's an easier method. You only need focal length and distance if the hyperfocal length starts to become significant.
You can try it for yourself. Select say a 2m subject, ie head to toe person standing, camera in portrait orientation.
Pick a focal length, say 50mm. Work out the distance you need to stand from the person to get them to fill the frame. Work out the DOF using one of the standard DOF calculators.

Now pick another focal length, say 200mm. Again work out the distance from the subject to get them to fill the frame. Again work out the DOF using one of the standard DOF calculators.

The answer will be almost exactly the same. Certainly close enough for the difference not to be important, relevant or even interesting.

If you can judge the size of the framed subject, or if the answer needs to be accurate measure it, and you know the aperture, you can work out the DOF.

Let's try it with the DOF calculator you suggested.
Let's make the camera subject distance 3m. Aperture f/2.8, 50mm on a 7D.

It says DOF = 0.38m

Now let's switch to 200mm, and move back to 200/50x 3m = 12m.
Plug in 200mm, f/2.8, 12m.

It says DOF = 0.38m

See, the same

So I've changed the focal length, changed the distance, and got the same answer.
So what did I REALLY need to know?
The size of the framed subject and the aperture. And IMO the size of the framed subject is pretty easy when taking pictures of people. They are about 2m tall, head to waist about 1m, width of shoulders about 600mm.

The result is this table:

What can be learnt from this?

1st, for the same resultant image, ie the same framing of a subject, changing focal length (the having to change distance), doesn't change the DOF. So don't try and get a shallower DOF by changing focal length. Yes the OOF part of the image will look different, but not the in focus part.

2nd, see how the DOF gets shallower as the size of the framed subject shrinks. That means if taking pictures of big things, the DOF will be bigger than when taking pictures of small things. To maintain a similar DOF, you'll need to change aperture as the size of the subject changes.

3rd, it's difficult to get a large DOF when taking pictures of something 300mm in size, like a face.

4th when the subject size is about 4m or more, and you start using f/8 or more, the hyperfocal length starts to become important, so use a DOF calculator. You'll be interested in the near and far limits and the hyperfocal length.

dan.k78 wrote in post #12512182
One thing I'm curious about though is having enough depth of field. I read a lot on this forum how many folks are shooting indoor ceremonies (and other less than ideal lit locales) at f/2.8 using some pretty nice glass (17-55 f/2.8, 24-70 f/2.8 & 70-200 f/2.8). At some of those longer focal lengths with apertures of f/2.8, the depth of field is crazy shallow; how do you keep enough of your subject in focus?

Using my table I can try and answer that.
So, using f/2.8, on a crop camera. (it'll be shallower on a FF camera).

If you take a picture of a standing person, head to toe, the DOF will be 850mm. Enough for their body to be in focus unless their hand is sticking forward.
If you take a picture of just a head, the DOF will be 18mm. You'll be wanting to use AI-servo, and the AF-on button, and probably even the centre AF sensor, aim very carefully at the nearest eye.

Correlation does not equal Causation. Distance from subject, focal length and aperture still are the critical pieces of data in your calculations, even if you've short-handed how you're reaching those numbers. In your own description you mention that if you change focal length, you have to change distance as well, in order to maintain the same DoF at a given aperture.

Whether you're thinking about, explicitly, that way or not you're still using those three pieces of info in calculating your setup.