Depth of Field - help?

NedM · Jan 2, 2014

I'm having a difficult time grasping the concept of Depth of Field.
To put it bluntly, I don't understand one bit of it.
From calculating distance from a subject to selecting appropriate aperture.

Ysarex · Jan 2, 2014

Hyperfocal Distance and Depth of Field Calculator - DOFMaster

Joe

Derrel · Jan 2, 2014

Here's a video that should really help!

tirediron · Jan 2, 2014

Try this

and this.

KmH · Jan 2, 2014

Depth of field - Bing

You don't need to calculate the distance to a subject.

Several factors effect how deep, or shallow, DoF is.
Subject distance, lens focal length, lens aperture, image sensor size (or more accurately - apparent field of view (FoV)).

You just need to understand that DoF is a zone of acceptably sharp focus essentially parallel to the plane of the image sensor.
The sharpest point in the photo is right at the point of focus (PoF). The zone of acceptably sharp focus extends in front of and behind that PoF.
How rapidly the zone of acceptably sharp focus in front of and behind the PoF changes is a function of how deep or shallow the DoF is.
When DoF is deep the change is very gradual. When DoF is shallow the change is quicker.
The distribution of the DoF in front of and behind the PoF is also not constant and can vary from 505 in front and 505 behind the PoF to 30%/70% or more.

If you want a blurry background, the further from the subject the background is, the easier it is to make the background out of focus (OOF) by controlling DoF.

NedM · Jan 2, 2014

Derrel said:
Here's a video that should really help!

This video really helps me understand the concept of how changing the aperture will affect the DoF.

But I'm also having trouble understanding this:

A quote from KmH on DoF from a previous post.
"A 50mm lens on a crop sensor (1.6x) camera, with its aperture set to f/4 and the point of focus at 10 feet ha s total DoF of 1.84 feet.
A 100mm lens on a crop sensor (1.6x) camera, with its aperture set to f/4 and the point of focus at 20 feet has total DoF of 1.83 feet."

When KmH talks about, the point of focus at 10 feet has a total Dof of 1.84 feet, what exactly does this mean?
Where can I learn more about what KmH is talking about here?

480sparky · Jan 2, 2014

NedM said:
When KmH talks about, the point of focus at 10 feet has a total Dof of 1.84 feet, what exactly does this mean?
Where can I learn more about what KmH is talking about here?

The camera lens is focused at 10feet. The total DOF around that 10' point is 1.84 feet. You can have two subjects, 1.84 feet apart (inline with with the camera) and both will appear in focus. It may be 9.16 feet to 11 feet.

SCraig · Jan 2, 2014

Look at the sketch below the calculation area on This Page. It explains it perfectly.

bratkinson · Jan 3, 2014

I generally think of DOF as an invisible wall of 1" thick plywood, parallel to the camera sensor. Everything 'within' that wall at the exact focus point (end of someones' nose?) is in very sharp focus. Added layers of plywood front and back from that first layer are just a little bit not quite as in focus as that 1" original layer. Each successive layer added front are slightly less sharp than the one previously added. At some point, the degree of 'un-sharpness' is unacceptable and considered blurred. The total distance between the frontmost and rearmost layers is the Depth of Field...eg, the 'thickness' of what is in acceptable focus.

In other words, the focus point is a small point in space where the camera focused 'exactly', with about equal distances front and back 'acceptably focused'...aka DOF...at least that's the way I think of it without having to use calculators or mental gymnastics to figure out what my DOF is for a shot.

Then I think of either 'more' or 'less' DOF do I want in a shot. Smaller apertures or backing away from the subject both increase the DOF. Larger apertures (especially f2.8 and larger (smaller f-numbers)) get smaller and smaller DOF...even down to an inch or so when quite close and at or near wide open with a large f-stop. Another 'twist' to DOF is the longer the focal length, such as a 70-200mm lens zoomed to 200mm, the DOF will be considerably thinner than, say, a 50mm at the same f-stop, same camera, same distance from the subject.

Take some time to 'play with' the DOF calculator Tirediron linked to. Then go out and shoot some shots with various apertures and focal lengths from a tripod. Check the results. I find this 'geezer' mind of mine works quite well at "f2.8 and larger...thin DOF. F4-f8 (or f10)...medium DOF, f11 and up...lots of DOF!

KmH · Jan 3, 2014

SCraig said:
Look at the sketch below the calculation area on This Page. It explains it perfectly.

I like the way this online calculator displays the DoF distribution too - http://tawbaware.com/maxlyons/calc.htm

timor · Jan 3, 2014

NedM said:
I'm having a difficult time grasping the concept of Depth of Field.
To put it bluntly, I don't understand one bit of it.
From calculating distance from a subject to selecting appropriate aperture.

Lots of help here. On DoF and more:
the Photograph

rambler · Jan 3, 2014

For simplicity try this: take the focal length of your lens and divide by 3. 12mm divided by 3 = 4 Focus for feet in. To get maximum DOF.

For DX formats, multiple the mm by 1.5, then divide by 3.

This method works when you want maximum DOF, sharp focus throughout, so use the smallest aperture.

480sparky · Jan 3, 2014

rambler said:
For simplicity try this: take the focal length of your lens and divide by 3. 12mm divided by 3 = 4 Focus for feet in. To get maximum DOF.

For crop factors, DX formats, divide by 3 then multiple by the crop factor, usually around 1.5 to keep it simple. 1/2 of 4 is 2, so 4 +2 is 6 which is the same result as 4 x 1.5 Who needs calculators?

Um, don't you need something like......oh.................... I don't know.......................... something like .................. the lens aperture setting? :er:

slindsey137 · Jan 3, 2014

Please excuse my piggyback. A friend wants me to take a photograph like this . I have been trying to practice it, but I can't seem to make it work with my 18-55 mm lens. It is currently the only one I have. I can't get anything wider than f/5.6 with it. Any suggestions on a new lens?

NedM · Jan 3, 2014

slindsey137 said:
Please excuse my piggyback. A friend wants me to take a photograph like this . I have been trying to practice it, but I can't seem to make it work with my 18-55 mm lens. It is currently the only one I have. I can't get anything wider than f/5.6 with it. Any suggestions on a new lens?

You're gonna need a lens with a wider aperture.
Try 50mm 1.2, 1.4, or the 1.8