Aide Memoire for Depth of Field

[Tom Axford]

Instead of using depth of field calculators (such as this), I find it easier to keep a small card in my wallet that tells me:

For Micro Four Thirds cameras set at f/4
DoF is 25cm for a subject frame of 80x60cm
(DoF varies as the square of the frame size,
and DoF varies in proportion to the f-number)

This information is sufficient for me fairly easily to estimate the depth of field for any frame size and any f-number (aperture), within reason. In most cases it gives a very good estimate.

The DoF varies with the square of the frame size (any dimension you choose). So, if the frame size is 40x30cm, the DoF is 6cm; and if the frame size is 1.6x1.2m, the DoF is 1m.

Probably most photographers already know that the DoF is proportional to the f-number. So the DoF is twice as much at f/8 as at f/4, and half as much at f/2 as at f/4. This enables you to work out the depth of field for any f-number.

The subject frame simply means the size of the field of view in the plane of the subject. In other words, a subject of that size exactly fills the viewfinder.

There are some limitations on this method. If the subject is more than about one third of the hyperfocal distance away, then the DoF becomes significantly larger than the value given above (and is infinite beyond the hyperfocal distance).

At the other extreme, the DoF calculated in this way may be incorrect if the frame size is close to the sensor size of the camera (i.e. true macro photography). However, most depth of field calculators also give incorrect results for true macro photography.

I don't think this method of working out depth of field is very widely known and I am posting this in case others may find it useful.

 

[UrbaneHobbit]

Seems like this is something the camera could work out and display on-screen while the user is focusing and manipulating the aperture!

 

[Tom Axford]

Seems like this is something the camera could work out and display on-screen while the user is focusing and manipulating the aperture!

Yes, it is certainly possible in principle.

However, I would still like to be able to work out the depth of field in advance of picking up the camera.

 

[Adrian Harris]

Seems like this is something the camera could work out and display on-screen while the user is focusing and manipulating the aperture!

Yes, it is certainly possible in principle.

However, I would still like to be able to work out the depth of field in advance of picking up the camera.

The beauty ofive view is it will display this for you. Can't remember what it's called at the moment, but I have it assigned to a button. When I press it, everything in focus is highlighted by a colour of my choice.

I first used it 10 years ago when unexpectedly coming across a beautiful view at dusk but had no tripod. I thought I would have to stop down so much to include the foreground as well, but the in focus highlights revealed that I could have the shutter open quite wide - and enough do that I could get s high enough shutter speed to hand hold.

 

[Tom Axford]

Seems like this is something the camera could work out and display on-screen while the user is focusing and manipulating the aperture!

Yes, it is certainly possible in principle.

However, I would still like to be able to work out the depth of field in advance of picking up the camera.

The beauty ofive view is it will display this for you. Can't remember what it's called at the moment, but I have it assigned to a button. When I press it, everything in focus is highlighted by a colour of my choice.

I first used it 10 years ago when unexpectedly coming across a beautiful view at dusk but had no tripod. I thought I would have to stop down so much to include the foreground as well, but the in focus highlights revealed that I could have the shutter open quite wide - and enough do that I could get s high enough shutter speed to hand hold.

Yes, focus peaking can be useful in that way.

More often, I just take a test shot and review it under magnification to see how much is in focus and how much is not. Being able to take a test shot and review it instantly is a huge benefit of digital cameras.

Despite being able to check the depth of field in these ways, I like to understand the theory as well. If I am planning a shot well in advance, I like to estimate the depth of field so that I know whether I can use a large aperture and fast shutter speed or if it will be necessary to stop down to get everything I want in focus.

I find it very helpful to keep a simple aide memoire to enable me to quickly estimate the depth of field in any normal situation.

I started this thread to share my aide memoire with anyone who is interested. There are, of course, many other ways of doing it.

 

[Adrian Harris]

Seems like this is something the camera could work out and display on-screen while the user is focusing and manipulating the aperture!

Yes, it is certainly possible in principle.

However, I would still like to be able to work out the depth of field in advance of picking up the camera.

The beauty ofive view is it will display this for you. Can't remember what it's called at the moment, but I have it assigned to a button. When I press it, everything in focus is highlighted by a colour of my choice.

I first used it 10 years ago when unexpectedly coming across a beautiful view at dusk but had no tripod. I thought I would have to stop down so much to include the foreground as well, but the in focus highlights revealed that I could have the shutter open quite wide - and enough do that I could get s high enough shutter speed to hand hold.

Yes, focus peaking can be useful in that way.

More often, I just take a test shot and review it under magnification to see how much is in focus and how much is not. Being able to take a test shot and review it instantly is a huge benefit of digital cameras.

Despite being able to check the depth of field in these ways, I like to understand the theory as well. If I am planning a shot well in advance, I like to estimate the depth of field so that I know whether I can use a large aperture and fast shutter speed or if it will be necessary to stop down to get everything I want in focus.

I find it very helpful to keep a simple aide memoire to enable me to quickly estimate the depth of field in any normal situation.

I started this thread to share my aide memoire with anyone who is interested. There are, of course, many other ways of doing it.

When worrying about a particular one chance attempt at taking a particular astro shot 2 summers ago, I thought I had better research Depth of focus to see if it were possible for the close foreground and stars to both be in focus at the same time.

I was shooting my em1-mk2 with the 7-14 f2.8 pro lens set at 7mm (14mm on FF).

I was shocked to find that even at f2.8 I could set the hyperfocal distance ridiculously close to me - something like 5 metres - and still get the stars in focus.

A trick I sometimes tried to help achieve a softer focus background in certain circumstances when I don't have a fast lens attached, is to focus slightly in front of the main subject. On the few occasions I have tried it, it has worked well.