Depth of field for beginners, really?

[anita]

Hello,

I have a big frustration, maybe someone could help me.

One day i've decided to get a camera and become a photographer.

I started to read a lot of stuff on internet about things like ISO, Aperture, Exposure,ecc.

I've came to this "problem" called Depth of Field.

I'm trying to understand it, but in my case is very difficult. I'm reading things, and i think maybe the ones they know about this don't want to share, or share 10% or less about it. . I've started reading the tutorial from CiC. Good tutorial in part, but AS A BIGINNER, i don't understand much. There is a drawing, talking about the Circle of Confusion, ecc. In the name of all the beginners in the world: We need EXAMPLES. I need example, how this things happens. You are not talking anything about the plan of the camera, how this changes, how this affects the DOF, what is Circle of Confusion? I don't know.

I would like to improve something in this world. , please help me, i'am a beginner, i only know what beginners don't know and don't understand.

As a conclusion: I like this site, very good, i like the articles, just that i can't figure it out how things functions. As we get more experienced, we tend to forget how to explain to the beginners.

Thank u very much for your time, a dissapointed "wanna be" photographer.

[Colin Southern]

Hi Ana,

My suggestion is to forget "Circles of Confusion" (I don't understand them either!).

Basically, all you need to remember is ...

1. The SMALLER the F-Stop number (eg F2.8 - the bigger the hole that lets in the light - and the LESS DoF you'll have.

2. The BIGGER the F-Stop number (eg F22) - the smaller the hole that lets in the light - and the MORE DoF you'll have.

[anita]

Ok, this things i understood. Maybe are the only things clear to me.

But let's go deeply. If i have as a subject a glass for example. If i change the position of the camera(going down,up,left,right), how does this affect the DOF? After that, there is the DISTANCE FOcus, how this one affect the depth of field, and not to forget of the Focal length. What is the focal plane of the camera, what is the focus plane, or whatever is called? . If i want to take a picture i must know how to use my camera, or every photographer goes on LUck?!?

Don't you like to understand what is this Circle of Confusion? My mind functions like a "compilator". It reads the sentence and when arrives at a word that doesn't know/understand, sends an error and stops! If i pass over this i pass over all things that i don't understand!

Good day . I'm optimistic that someone would help me/you :P.

[Goldcoastgolfer]

What might also help is of you post some examples of pictures, the settings you used, and what you were trying to achieve. People here can then provide you with some guidance on how you could have done that using your own photos.

[CougarFool]

Anita,
Years ago I did an experiment to try and understand it.

I found a repeating pattern that went off towards the horizon. A brick wall, a line of closely spaced trees, some gravestones in a cemetry (Yes really!).
A tripod is handy but not essential.
Set the widest aperture on your lens (f2.8 for example) and focus in the middle of the repeating feature.
Take a picture.
Set the next aperture.
Focus in exactly the same place
Take a picture.
Repeat until you have worked your way up to the narrowest aperture (f22 for example).

Review each picture paying particular attention to what is in focus and what isn't.

(I am at work so I can't post an example image.)

This will help you understand DoF better.

[MrB]

It is said that the best way to learn is to teach so, as a relative beginner, I will try to pass on the basics from that perspective (excuse the pun) and hope I've got it right.

Depth of field is the part of the scene that appears to be in focus (clear, detailed, not fuzzy) as you look from near to far in the image. So, with a short depth of field, only the thing you focused on (and other things at the same distance away) will seem clear, things in front and behind will seem fuzzy. But with a longer depth of field, you will see things both nearer and further away than the focused object seem also to be clear. With the correct camera settings depth of field can be made to seem infinite - everything from near to far will be clear, as in a landscape photo.

Taken separately, the things that apparently decrease depth of field are -
shorter distance to the focused object
longer focal length lens (i.e. towards telephoto)
wider aperture (i.e. smaller f number)
bigger camera sensor (i.e. length and width)

When these are taken together, the effect will be compounded.

Hope this is a start.

Philip

[Fit]

These images might help you visualize a bit better: http://www.exposureguide.com/focusing-basics.htm

[rtbaum]

Ana- In regards to "the circle of confusion", it sounds like some one's cute phrase that they use for depth of focus. I would not concern myself trying to decode the phrase. To determine depth of field for a given lens at your stage of the learning process; place a series of objects on a table in line and offset from each other, mount your camera to your tripod (or stabilize). Focus on the closest object. Make a series of exposures at f/2.8, f/16, f/22. You will notice that the object that you focus on will be sharp in each shot. what will change with each change in f-stop will be the focus on the other objects will change.
F/22 will have a greater depth of field, f/2.8 will have a smaller depth of field.

Focal plane is your film or image sensor in the camera, focal distance is the distance from focal plane to the object that you are shooting.

Now move your camera forward or backward and shoot another series at the f/2.8, f/16, f/22 and note how this changes depth of field. You should note that decreasing focal distance decreases depth of focus; increasing focal distance increases depth of field.

Focal Length refers to the size of the lens and this will also change the depth of focus. A 28mm lens will have a larger depth of field than a 300mm lens.

[Graystar]

Have you ever used a magnifying glass to burn something with the light of the sun? That tiny little spot of light is a sharp, focused sun. When you move the magnifying glass closer or further from the paper (or unfortunate ant...depending on how old you were) the spot turns into a circle. That is a Circle of Confusion. It's what you get when you're out of focus.

When you focus on something with your camera, only objects at the focus distance are sharp because the light is focused into points of light (like the focused sun through the magnifying glass.) Objects that are further or closer than the focus distance will be circles instead of points.

If you had played with a magnifying glass as I described, you would have noticed that the size of circle gets bigger the further away you move the magnifying glass. The more out of focus, the bigger the circle. This also happens with the camera. Objects at your focus distance are sharp points. Objects just a bit outside of your focus distance (either closer or further) are making little Circles of Confusion. Objects that are further away from your focus distance are making big Circles of Confusion.

There is a formula, based on human acuity and the size of the printed image, that determines (roughly) when human eyes will notice the Circles of Confusion. When the circles are smaller than human perception, the image is still considered sharp. The range of distance from the point of focus, where the circles are too small to notice, is the Depth of Field. Objects outside of the Depth of Field start to look fuzzy because the circles are big enough to see.

[anita]

First of all, thank you all for your answers!

@Goldcoastgolfer. It's not about a single image. I want to, when i see a subject, to put the focus point in a place, and now in the end what it would be its the depth of field. For example, i want to focus a baby face, only his nose, or something, and not to HOPE that it was enough DOF. I want to understand very well this DOF and what implies to be able to control my images, not to arrive home, download photos and Oh! Her eyes where not in focus, or her ears, or an eye in focus and the other one not, ecc. (i think this has to do with focal plane/camera's plane, which i don't understand what it is, i can't visualize it in the real world).

@rtbaum
:'(, oh, now i see that's another aspect? DOF of a lens? Hope not.

Now move your camera forward or backward and shoot another series at the f/2.8, f/16, f/22 and note how this changes depth of field. You should note that decreasing focal distance decreases depth of focus; increasing focal distance increases depth of field.

Focal Length refers to the size of the lens and this will also change the depth of focus. A 28mm lens will have a larger depth of field than a 300mm lens.

.

The part with decresing focal distance(getting closer to the subject-understand) decreases depth of focus(new term, don't understand + Depth of focus = circle of confusion ?!?), increasing focal distance(getting away from the subject) increases depth of field(did you mean depth of focus, or in both cases you meant depth of field?).

@CougarFool
I don't have a cemetry near, i will try to experiment on pencils or whatever i found in house. Thank you, i will try your advice. Olso thanks to rtbaum for this advice.

@MrB
:'(, You've inserted a new element in our "equation" - camera's sensor size.

Pls don't get mad on me, it's not my fault, my mind is locking and doesn't unlock until it receives an OK answer(and accept it).

PS: For example, if i put 1000001 pencils in a row on a table and focus in the middle (don't know exactly where my camera should be-in term of angle- to see the DOF), and set a 5.6 aperture, will i see all 1000001 in focus??? the DOF let's say is 12 cm (4 in front&8 rear). How far this focus would go to the left and how far to the right?

THank you very much to all of you.

[russellsnr]

Hi, I always find that seeing the answer to the question on this kind of subject is a lot easier than reading about it so please have a look at this tutorial on DOF it is not very long but may help you understand it a bit better.
http://www.youtube.com/watch?v=OUYuUs1aaCU
Thanks
Russ

[Snarkbyte]

Hi Anita. There is a good reason why you don't need to worry much about circle of confusion: there's nothing you can do about it. For any particular model of digital camera, the circle of confusion is a fixed constant, determined by the camera's sensor. If you really need a number, you can probably find a value for the circle of confusion for your camera at this website: http://www.dofmaster.com/digital_coc.html

In the context of DoF, the circle of confusion is really just the size of the smallest distinguishable feature on the image (not the on subject, but the on image made by the lens)... in other words, it's the size of a single pixel element on the camera's sensor. (OK, strictly speaking, that isn't quite true for most digital cameras, but you can think of it that way). That's why the circle of confusion is a constant for a particular model of digital camera... it's built into the sensor design, and aside from buying a new camera, there's nothing you can do to change it. It's a bit more complicated with film camera's because in that case, the circle of confusion is (usually) determined by the granularity of the film.

[anita]

Have you ever used a magnifying glass to burn something with the light of the sun? That tiny little spot of light is a sharp, focused sun. When you move the magnifying glass closer or further from the paper (or unfortunate ant...depending on how old you were) the spot turns into a circle. That is a Circle of Confusion. It's what you get when you're out of focus.

When you focus on something with your camera, only objects at the focus distance are sharp because the light is focused into points of light (like the focused sun through the magnifying glass.) Objects that are further or closer than the focus distance will be circles instead of points.

If you had played with a magnifying glass as I described, you would have noticed that the size of circle gets bigger the further away you move the magnifying glass. The more out of focus, the bigger the circle. This also happens with the camera. Objects at your focus distance are sharp points. Objects just a bit outside of your focus distance (either closer or further) are making little Circles of Confusion. Objects that are further away from your focus distance are making big Circles of Confusion.

There is a formula, based on human acuity and the size of the printed image, that determines (roughly) when human eyes will notice the Circles of Confusion. When the circles are smaller than human perception, the image is still considered sharp. The range of distance from the point of focus, where the circles are too small to notice, is the Depth of Field. Objects outside of the Depth of Field start to look fuzzy because the circles are big enough to see.

It's an interesting point of view(discover that it's not A SINGLE CIRCLE of CONFusion, are more of them ). This has to do with bokeh when people analyze the "roundness" of the ligths that's on the background)?. Sorry still not clear about the subject.

Becoming more and more interesting. Thanks!

[William W]

What camera do you have?
What lens(es) do you have?

WW

[anita]

Another implication of the circle of confusion is the concept of depth of focus (also called the "focus spread"). It differs from depth of field in that it describes the distance over which light is focused at the camera's sensor, as opposed to the subject...

. Says here on this site.

On the other hand, looking to the video on youtube (Mark Wallace/Adorama TV-> recommended by russellsnr http://www.youtube.com/watch?v=OUYuUs1aaCU) right when the movie starts, someone asks him about the " ....'DEPTH OF FOCUS', and he corrects him DEPTH OF FOCUS is called "Depth of Field"..., so for him the 2 things are the same =>Depth of Field).

@William W - 5DMII + 24-70 f/2.8 Canon.

I don't understand it anymore :'(. The more i search the more it's becoming so confuse.

[JonathanC]

Absolutely spot on with the bokeh thing Anita. The round blob that people like as "bokeh" in images is the circles of confusion. The blob usually translates from a bright point source that was either further away or closer in than the focus distance. When the circle of confusion gets that big it is actually really far out of focus, so the CoC is very big. If the desired result on your image is to get a good sharp image of whatever the bright highlight is, you would adjust the focus. As the focus gets better the blob changes to a brighter, smaller blob and then on to being a correctly focussed highlight thingy wotsit. The shrinking happens as the CoC gets smaller, because the focus is closer to being correct, for the highlight. It may not be correct for the image that you want to make, which may be a friend stood outdoors with a street light behind them.
Now that you've actually seen a CoC, lets discuss what the rest of it is all about. The lens focusses the light coming in through the front to a sharp image. If that sharp image is in the same place as the sensor of the camera, you'll get a sharply focussed image. This assumes that your target is two dimensional, like a flat wall that you're looking at straight on. As most scenes that we shoot are three dimensional, you have to choose which part to get in focus. Adjusting the focus moves the lens towards or away from the camera sensor (in simple terms at least, let's not get too clever yet) and changes which bits of the scene are in focus.
If you can, imagine the scene in front of the camera reproduced, inverted, inside the camera. One "slice" of that scene is in the same place as the camera sensor. Thats the bit in focus, a slice which you can imagine as a wall in front of you, actually inside the three dimensional scene that you're shooting.
Lets say you have a camera set up outside on a tripod at night and a car drives past you. As the car gets towards the point of focus, the tail light "bokeh blob" gets smaller until it reaches the point of focus, at which point you could take a sharp image of the back of the car. As it moves past the point of focus, the "bokeh blob" gets bigger again.

The aperture changes how quickly things not in focus go out of focus as the distance changes. With a smaller aperture (higher f/ number) the out of focus things will be less out of focus than with a larger aperture. Here's why.
Think of the light from a distant highlight coming in the front of the camera and focussed to a point. You can imagine this as a cone of light as the lens iverts the mostly parallel light rays to a single point on the sensor. If you have a smaller aperture, the cone of light is more pointy as the length of the cone stays the same, but the aperture is smaller. If the aperture is very small, the cone is very pointy. This means that the diameter of the cone grows from a point to a circle more slowly the more pointy the cone. Consequently the CoC of out of focus things is smaller, or less out of focus.
I do hope that this makes sense to somebody else.

[anita]

Nope, still my mind is locked, perhaps you have it very clear in your mind, i tried to understand what you are saying, but much not, sorry, i''am appreciating A LOT, i do .

The lens focusses the light coming in through the front to a sharp image(understood). If that sharp image is in the same place as the sensor of the camera, you'll get a sharply focussed image.

What did u mean with sharp image is in the same place as the sensor of the camera? the camera is on your hand, the subject is at a distance? Same place where, how? what angle? what direction? :'(. Confuses me. I need a simple explanation, maybe a RETARTED explanation, why not a DRAWING, lol .

Thank you very much, JonathanC .

[JonathanC]

Nope, still my mind is locked, perhaps you have it very clear in your mind, i tried to understand what you are saying, but much not, sorry, i''am appreciating A LOT, i do .

What did u mean with sharp image is in the same place as the sensor of the camera? the camera is on your hand, the subject is at a distance? Same place where, how? what angle? what direction? :'(. Confuses me. I need a simple explanation, maybe a RETARTED explanation, why not a DRAWING, lol .

Thank you very much, JonathanC .

You are more than welcome.
What I mean is that if you have your camera pointed at something, it gets focussed by the lens to a sharp image. It just doesn't always line up with the sensor. You could point just the lens at something to see what's going on, out of a window on a bright day is usually good. If you put a piece of white card behind the lens you'll get an image. If you put the card in a certain place, the image will be in focus. If you put the card closer to the lens, or even slightly further away, you'll see a poorly focussed image on the card. The in-focus image is still there though, you just can't see it until you put the card where it is.
Similarly, you need to put the camera sensor where the focussed image is to get the shot in focus.
Just believe that the scene is there, focussed by the lens, in miniature and upside down at the other end of the lens, and it may make sense.

[William W]

Thank you for answering.

Your camera has a DoF (Depth of FIELD) Preview Button - it is located just near the “Mark II” symbol. (p93 user manual).

It's not about a single image. I want to, when i see a subject, to put the focus point in a place, and now in the end what it would be its the depth of field. For example, i want to focus a baby face, only his nose, or something, and not to HOPE that it was enough DOF. I want to understand very well this DOF and what implies to be able to control my images, not to arrive home, download photos and Oh! Her eyes where not in focus, or her ears, or an eye in focus and the other one not, ecc. :

An In the field Guide, for portraiture: you can use my DoF (Depth of FIELD) Cheat Cards for your camera format.

And once you establish a good sense of subject size, you can substitute an imaginary person into the scene: for example if you are taking a photograph of a bowl of fruit - that is about the same size as taking the headshot of a person – etc.

These DoF Cheat cards are in Imperial Measure (inches and feet) and are conservative in that there will be a little more DoF than actually indicated and also they allow (for the Full Length Shot) about 12” below the feet and 12” above the head and are for an average male person being 6’ tall.

DoF for the Intermediate Apertures can be easily approximated.


DoF Cheat Card for 5DMkII for Vertical Framing:


***

DoF Cheat Card for 5DMkII for Horizontal Framing:



***

( (i think this has to do with focal plane/camera's plane, which i don't understand what it is, i can't visualize it in the real world)

Technical notes:

The camera’s Focal Plane is a POSITION on the camera from which MEASUREMENTS (usually to the SUBJECT) are made.

The POSITION of the Focal Plane on nearly all cameras is indicated by the symbol: ϴ

On the 5DMkII, this symbol to indicate the position of the Focal Plane, is located on the top-side of the camera’s Pentaprism Hump (near where you slide the Flash in), and just above the Camera’s Mode Dial Knob (the knob you turn to select B Tv; Av; M . . . etc)

. right when the movie starts, someone asks him about the " ....'DEPTH OF FOCUS', and he corrects him DEPTH OF FOCUS is called "Depth of Field"..., so for him the 2 things are the same =>Depth of Field).

Depth of Focus and Depth of Field are DEFINITELY NOT the same thing.

I suggest at this stage, if you want a practical / working understanding Depth of Field that you do not concern yourself with Depth of Focus


WW

[Andrew1]

As with a lot of the technical details of photography both film and digital, all this stuff is easy to understand, once you understand it. It is difficult for beginners but stick with it. Keep reading and experimenting. One day something will click and you'll have your AAH-HAA moment when you understand a particular learning. The Circle of Confusion has been a reference since forever. Some people call it different things but the principal is still the same. You only have one finite plane that is truly in focus and light from objects in front or behind that point are not. The extent of the out-of-focus range and how fast it changes is dependent upon the light and how it is manipulated. Distance to the subject, the focus point and the amount of light all play a part. Our eyes work pretty much the same way as a fixed focal length lens. Look at things close up and far away and you'll see the same effect of more or less being able to see the details. Patience. It will come.