Depth of Field ~ distances and zoom lenses

[ac12]

I actually used the DoF scale when I set the focus of my film cameras.
Even my father's old 1950s Exacta had DoF scale.

With a 2-ring zoom on a dslr, I end up either ignoring DoF, or hoping I got enough by using a small aperture.

And worse, the focus rings on the Nikon 18-140 and 35/1.8 do not even have a distance scale. So you cannot easily use a DoF calculator/app, even if you wanted to. To set the focus, you have to get the camera to autofocus on something at the distance the calculator/app indicated, then turn off the AF.
1 step forwards, 1 step backwards.

 

[ac12]

For me DoF was part of basic composition, and I used it a LOT. And I was not and am not a pro.
As I composed the image, I would also compose the DoF.
For a scene, if I want from the post to the tree in focus, what DoF do I need?

• I would use the lens to "rangefind" the distance to the post and the tree.
  
• Then look at the scale and rotated the focus ring till I got the distance to the post and the tree in the scale.
  
• The selection of the aperture on the scale defined the aperture I needed to use.
  
• Which then defined the required shutter speed for that aperture.

The procedure takes more time to write and edit, than the 5-10 seconds to actually do it in the field.

Today DoF is mostly guessing.
I look at the scene and focus at a point 1/3 back from the front of the range of what I want in focus.
Then select a small aperture (like f/16), and hope that I have enough DoF.
Without a scale, I don't know with any certainty what aperture to select; 5.6, 8, 11, 16, 22, 32.
And selecting the aperture it isn't simple, because DoF varies based on focal length. Look at the curved DoF scale line on the pix of the Nikon zoom that Derrel posted.
Can I use a larger aperture to use a higher shutter speed? Without the scale, I have no idea.

If you have never used a lens with a DoF scale, you really don't know what we are talking about.
Because you have to use it, to understand and really appreciate, how well something so simple works.
It is so much easier and faster to use than an app.

An issue with the app and the lens is reliable distances.
My DX lenses do not have a rotating distance scale. So I cannot use the lens as a rangefinder. I have to guess/estimate the distance to the close point, far point, and the point that the app tells me to focus on. If I don't guess/estimate the distances correctly, I get an incorrect answer, and focus at the wrong distance. Garbage In, Garbage Out.

 

[Derrel]

A DOF scale is VASTLY quicker than an app, and since it is an analog display, it allows one to see multiple parameters at one time, very quickly. On shorter lenses, 20 to 85mm, the DOF scale on vintage lenses is often quite useful in actual picture-taking. It's also possible to set focusing distance, an adjust the DOF that way, and then to close-down the lens first one, the two stops, to get more, deeper DOF, and to have slightly different shots to choose from.

A good DOF scale also allows exceptionally quick ascertainment of the hyperfocal focusing distance needed for the various f/stops.

Pre-focusing or "focusing by scale" is very easy with a lens that has a good DOF scale!

After a decade of shooting pictures, I started doing more and more focusing by hand-and-eye, with the depth of field preview held in, and me determining the best focus distance "by eye".

In the d-slr era...it's very easy to literally shoot a picture, and then review the DOF effect, on the spot.