Christian Photographers Community

Depth of Field
A Tutorial for www.christianphotographers.com
by Bernard Shuford

General Notes
"Depth of field" is one of those photography buzzwords that most advanced beginners basically understand but can't necessarily control.  Beginners have heard it but don't know what it means.  Experienced amateurs are usually pretty good at it but may get confused sometimes.  Professionals know that their very livelihood lies in understanding and using Depth of Field properly.  

Depth of Field is second only to Exposure when it comes to properly using your camera and its associated lenses.  Composition is critical, yes, but DOF can be a compositional tool and will affect your composition in many ways.  Subject selection is critical, but DOF controls how well you highlight your subject, if at all.  Lighting is important, but understanding and properly using DOF can cover many "sins" in that area as well.  

Flashes - This tutorial is generally written toward non-flash photography.  Flash sync speeds terribly affect exposure options, thus eliminating many of the ways we can use Depth of Field to our advantage.  To do what I talk about here, you really need to turn your flash off completely.  (Just as a side benefit, your photos will start looking different, and generally better.)

Fully Automatic Cameras - Fully automatic "point and shoot" cameras, whether film or digital, are at an extreme disadvantage when it comes to using Depth of Field as a photographic tool.  To experiment with DOF, you at least need to be able to select some type of "aperture priority" mode on your camera.  This is not an unusual feature, but some cameras may not have it.  Regretfully, most of what I am about to write will be useless to you with such a camera.

Aperture Priority - On autoexposure cameras (nearly all cameras, these days), DOF control is normally accomplished by using Aperture Priority mode.  This allows you to select the aperture size you want to use, and the camera will automatically set the shutter speed to obtain the correct exposure.  Be careful, however, that you are not forcing your camera to over- or under-expose your shots.  Some cameras do not properly alert you when you are forcing over- or under-exposure, and this can sometimes be a problem.  Pay attention to this until you learn how your camera works.  

Film vs. Digital - The actual medium itself has little effect on DOF.  However, the typical construction of digital cameras affects the results, and many point-and-shoot film cameras have the same problems.  Film SLR cameras, and possibly digital SLRs, very easily illustrate the effects of DOF, but the general rules are true through the whole gamut of photography.  This tutorial is primarily written to explain the ideas, rather than purport one camera's operation.  It is left to the reader to study your Owner's Manual and learn how to apply these things to YOUR camera.  

Basic Definitions

Let's get some basic ideas under our hats.  

Depth of Field

Depth of Field is really not a complicated thing.  Writing a simple definition has proven to be difficult, though.  

Let's divide a picture into three sections - foreground, middleground, and background.  Let's "pretend" that everything in the foreground is out of focus, everything in the middleground is IN focus, and then everything in the background is out of focus.

The Depth of Field is how "deep" the middleground is in our picture.  There is no measurement for DOF, just the idea of "more" or "less".  

Let's pretend our picture is of ten men, each one taller than the one before, and all standing one behind the other, so that the tallest one is in the back.  If we took a picture of these ten men, we would want them all to be "in focus", so that we could recognize them.  

"More" depth of field would be equivalent to all ten of the men being in focus.  "Less" depth of field would be the situation where only a few of the men are in focus, maybe half of them, with a couple in front and a couple in the rear being out of focus.  

The Aperture

The aperture is the "hole" which allows light to reach the camera's sensor or film. Larger holes allow more light to come through in a shorter timw, so faster shutter speeds are acceptable.  Smaller holes require more time for a given amount of light to enter, so slower shutter speeds are required.

Aperture sizes are expressed as "f-stops".  The technical abbreviation is "f/some number", where the "f" stands for "focal length".  Examples are f/11, f/8, f/22.  These are FRACTIONS, which actually indicate the size of the hole (in millimeters) as a fraction of the lens focal length.  We've all heard of 200mm lenses.  A 200mm lens with an f/22 aperture opening would have an actual opening of 9.09mm (200/22).  However, that piece of math is never performed in photography - only the "f-stop" number is used.   (Typically written f/11, f/8, or f/22, but said "f 11, f 8, f 22").

There are two basic rules to memorize -
   Rule A. Little NUMBER, Little FOCUS, Big Hole
   Rule B. Big NUMBER, Big FOCUS, Little Hole
         
Write these on the inside of your eyelids and repeat them to yourself to go to sleep.  Back to our ten men.  With Rule A, only two or three of the men will be in focus.  With Rule B, all of them could be in focus.  Of course, knowing the rule doesn't mean much if you don't know what to do with it.  

For example, f/2.8 is a LITTLE number.  That means I have a BIG hole for the light to enter, and the amount of my picture that is in focus will be LITTLE.  f/22 is a BIG number (much bigger than most digital cameras allow).  This means there is a LITTLE hole that lets light in, so the amount of my picture that is in focus will be BIG.

If you just memorize "Big number, big focus.  Little number, little focus", you will be off to a great start.  
         
The Science Behind DOF

This won't be a long section, because this is the boring stuff.  I only bring it up because it might help you remember how this works.

Little Number, Little Focus
When light comes through a big hole, it scatters more. Just think about your water hose when you set the nozzle for "spray".  This allows the water to "spread out" more, scatter more, and land softer and gentler.  This is very much like the way a big hole (large aperture) lets in light.  The light scatters a lot, which makes for a softer (more blurred) picture.
      
Big Number, Big Focus
This is a lot like setting your water hose nozzle to "stream".  The water enters through a small, constricted hole, and it hits a very small spot very accurately.  There is not much overspray, and the water does not hit "softly" at all.  Light through a small aperture (Big number, small hole) doesn't scatter very much, so there will be less blurring.  
      
Some Applications of Theory

Landscapes

Landscape shots are absolutely beautiful when executed properly, and many of my favorite shots are landscapes.  There are several focus techniques associated with landscape photography, some of which are virtually impossible with most digicams.  
   
Most landscapes are shot at infinity focus.  This is because the center point, where your camera focuses, is typically more than 60 feet away, and most camera lenses go into infinity focus at that distance or something even smaller.  
      
It typically doesn't look really good for a landscape shot to have blurry elements in the foreground.  It is really BEST if everything in a landscape is in focus, but there are always exceptions.  That's going to be reserved for somebody's composition tutorial.  I'm not writing that one!

The best way to prevent blurry foreground elements in a landscape, while using the typical point and shoot digicam, is to eliminate objects that are closer than about 50 feet from your picture.  If that is totally impossible, you can improve the picture by choosing a small aperture (BIG number, LITTLE hole).  This will improve your picture by making more of it come into focus.  

For anyone lucky enough to be using a digital SLR or a film SLR, YOU NEED TO LEARN HOW TO USE THE HYPERFOCAL CHARACTERISTICS OF YOUR LENSES.  It's easy to do with SLR lenses.  If you have manual focus on your digital camera, hyperfocusing is also possible, but it's well beyond the scope of this tutorial.  To be brief, hyperfocus is what is used to create those awesome professional shots that have acres of tulips all in focus, even right up to the camera, and the windmill half a mile away is also perfectly sharp.  

Portraits

Small DOF is often preferred in portrait photography in order to blur the background.  This is one of the ways the pros make the background look really "soft" while keeping the subjects sharp.  

It is also typically thought to be appropriate to use soft focus on portraits.  PLEASE DO NOT DO THIS BY INTENTIONALLY FOCUSING INCORRECTLY.  Soft focus is appropriately accomplished through filters or software.  ALWAYS focus on the subject when shooting portraits.  

Low f-stops (small number, small focus, big hole) also allow for fast shutter speeds.  This helps with subject sharpness.  

For added background softness, move the background far enough away to be out of the DOF. If you are using low f-stops, f/4 or f/5.6, moving the background about 3-4 feet behind the subject will cause a soft background effect.  

Still Life Shots

For entire pic to be in focus,try to position all components as close together as possible, then use higher F-stops (Big number, Big focus, Little hole).  If the subjects are separated by significant front to back distance, it is basically impossible for the entire picture to be in focus without moving back and zooming.  (DOF is "sort of" a percentage, in that the distance from the front of the in-focus zone to the rear increases as you get further away.)  

For blurry sections, use physical distance first, then decrease the f-stop (change to bigger hole, smaller numbers) one stop at a time until the desired effect is created.  This is sometimes done best, when using autofocus digicams or film cams, with trial and error or simply taking multiple shots.  Without the control that the photographer has with an SLR lens, it is often difficult to see exactly which sections of the photo are in focus and which are not, so multiple shots are very often required.  

Macro Photography

Subject Isolation - These are the shots where the flower is perfectly in focus and the background is incredibly blurred.  This cannot always be duplicated with non-SLR equipment, but it's fun to try.  Obviously macro capability is required.  Usually it's best to start with mid range f-stop in order to keep entire subject focused.  After taking shots at that setting, change to lower f-stop (smaller number, bigger hole) to increase background blur, but watch for subject blur.

Foreground AND background blur is possible by selecting a large aperture and then focusing on the middleground.  This forces a very small DOF, and it is very common to see the foreground go out of focus as well as the background.

Auxiliary lighting is nearly always required (unless you are in bright sunlight) when using small apertures.  Tripods are also normally required.  This is to keep shutter speeds as quick as possible.  Slow shutter speeds are not very useful with digital cameras (sensor "noise" is easily introduced"), but slow shutters are a favorite with professional film photographers, so they often do this without lighting.  

Conclusion

This concludes my basic tutorial concerning Depth of Field.  There are many more points to bring out; probably some basic ones that I either neglected or don't know myself.

I hope this has been helpful and I hope you have enjoyed reading it.  I plan to add some illustrations and photos in the near future.  

This is going to need some re-reading and study.  But I think I'm getting a little of it.  

Nard, this is good...and like Jeanne, I'll need to read and reread.  I've copied it to print.  I should get my new camera next week (decided on Olympus C-5050)so can't wait to start practicing this tut.

I think I am getting this. I will have to reread, I will copy and print this when my new computer gets here.

See, Nards?  You have us all thinking, at least.  Now whether all my thinking will bear any fruit is still another question.  

I just got my new camera today.    Betteries are charging, and tomorrow maybe I can go out and make use of the DOF tut.  Thanks again, Nard.

........and along with those "betteries", I decided to go ahead and charge my batteries too. Might as well get it all done tonight....doncha think?

Good luck to all of you  Please feel free to ask questions if this unintelligible prose makes no sense.  Still working on some sample pictures, too.

I drove out to my favorite rock this morning, and DOF was great on my one photo......everything was the same dull gray. haha  It's overcast and rainy today.   Maybe later I'll look elsewhere.

Oh my goodness... this is SO COMPLICATED... I'd never understand it...

Sure you will, Judy.  My biggest problem is not understanding the lesson.  It's remembering to apply it when I take a picture.  

YAY!!!!!!  I kept wondering what DOF (and aperature for that mater) was when people commented on my DPChallenge entries:
"More dof is needed." (on a current entry in which I absolutely love how it's focused, go figure)
"Nice looking rose. Good depth of field, subject pleasant contrasting with the background." (for this one)

I've been trying to do this (without knowing what it was called) with my automatic digital (Olympus D-550z).  The only way I can is to have the camera very close to the object and holding down the shutter slowly to allow it to focus on just the main object.

Would this or this be an example of it?  I know this is (it's the cropped version of the rose).

Quote from: Ami Yuy on November 26, 2003, 02:31:00 PM
YAY!!!!!!  I kept wondering what DOF (and aperature for that mater) was when people commented on my DPChallenge entries:
"More dof is needed." (on a current entry in which I absolutely love how it's focused, go figure)
"Nice looking rose. Good depth of field, subject pleasant contrasting with the background." (for this one)

I've been trying to do this (without knowing what it was called) with my automatic digital (Olympus D-550z).  The only way I can is to have the camera very close to the object and holding down the shutter slowly to allow it to focus on just the main object.

Would this or this be an example of it?  I know this is (it's the cropped version of the rose).

Your cropped version shows "more" depth of field in that "more" of the picture is in focus.  On the bigger version, you can see the very "bottom" of the rose is slightly out of focus, then the stem gets out of focus more, and then the lighter background is so far out of focus that it is unrecognizable, basically.  This is a very good, creative effect, and is basically exactly what this tutorial is about.  If you wanted even "less" of the picture to be in focus, you would use a "bigger" aperture, which means use a "smaller" number - f/2.8 instead of f/5.6, or whatever.  If you were to want to try to get the entire rose and perhaps some of the stem to be in focus, shoot the exact same shot with an f/11 instead of f/5.6, or whatever the numbers might have been.  Obviously the shutter speed has to go "faster" if you use a "bigger" aperture (smaller number) and "slower" if you use a "smaller" aperture (bigger number) to get the exposure to be right.  

I hope this helps  It's not a terribly difficult concept, but sometimes automatic cameras make it difficult to achieve the exact results you want.  

Limiting the depth of field (as you have done) by positioning the camera CLOSE to the subject is a very effective technique with automatic cameras, because they go into macro mode and focus at a very close range, which makes the background go out of focus.  It is often difficult to achieve "enough" depth of field (as much as possible, which usually requires "smaller" apertures - bigger numbers) to satisfy those pundits on DPC with a digicam.  I like the rose!!!

Great tuturial, Nards!

How are the sample pictures coming along, Nards?

Nards, do you have those illustrations that you spoke of?

I'm really interested in getting started on this.

Great explanation Nards.  I've recently started playing with DoF to get it right, while actually meaning to do it rather than get it by accident.  What is a great help is your advice of 'little number = little focus, big number = big focus.  That's the one thing I could never get my head around, but you've made it so that I can remember it now.  Thanks.

This was my latest attempt taken at f2.8  It worked out ok I think .. I'll keep practicing though.

Quote from: Pat Scott on July 22, 2004, 08:55:58 PM

How are the sample pictures coming along, Nards?

I guess I fell down on the job and never finished it, huh.  I'm not too much of a teacher   That's my wife's job. 
She could make a duck take swimming lessons.

Quote from: Annie on August 30, 2004, 06:24:25 PM
What is a great help is your advice of 'little number = little focus, big number = big focus.  That's the one thing I could never get my head around, but you've made it so that I can remember it now.Ã,  Thanks.

This was my latest attempt taken at f2.8.  It worked out ok I think .. I'll keep practicing though.

You've definitely got the idea right.  That's also a great shot.  The kind of camera you have controls how much you can blur the background, so I'm betting you have a point and shoot digital, right?  An SLR would blur that background significantly more at F2.8.  That's not a criticism at all, I'm just using the opportunity to point out the differences. 

Pat, I'm going to try my doggedest to get some shots up by the end of next week to illustrate.

Nards656 said..... I'm betting you have a point and shoot digital, right?

I have a Fuji FinePix S5000 so ..nope I don't have a DSLR at the moment.. more's the pity.  I originally was bought a Nikon Coolpix 2100, but found it very restricting as I tried different shots, so upgraded to the Fuji.  This was the best camera I could afford at the time.. I do like it and as I've only been photographing since December last year, I'm still learning, and I don't think my level at the moment is high enough to splash out on the UK prices of DSLR's.  One day maybe..

I know the feeling, Annie.  DSLRs are so prohibitive right now, but then 10 years ago, so were cell phones! 

P&S cams have smaller sensors, and the small sensor really makes a difference.  With a big sensor, the lens is actually further away from the sensor, which makes the F-stop have a much more drastic effect on depth of field.  As the sensor size shrinks, the lens gets closer to the sensor, and the blurring effect is decreased.  That's why most people have a difficult time really seeing this effect with digital photography.  The samples I hope to post next week will be done with a 35mm and will REALLY illustrate what this tutorial is about, but it will be difficult for those of us who use P&S digital to duplicate.  Soni and others who have DSLRs can come pretty close.

I'm glad to see you are understanding this.  It's one of the bigger reasons that I use my 35mm

This is something I want to do more of--learn about Depth of Field and practice it with the 8700.  I think it will be easier to accomplish than with my 950 Coolpix. 

Annie, I really like that photo.  You did a great job on it.

On my Christmas Wish List...

...that this tutorial be completed!  LOL  I really want to learn this.

I'm hearing you talk, Pat.  It's on my list, too !!!! 

Seriously, I've got to start shooting more.  Some of these things are hard to illustrate with a digital - for reasons I'll try to explain better - and I'm using my film camera again, since Trav has stolen my digital...

It's a priority.  I'll work on it!

Sending off some shots to the lab today that SHOULD be what I need to make this all make sense   Fingers are crossed.

LOL  Let me know when to uncross mine! 

Do I need to focus - pun intended :-) - on what DOF control can be used for, or more on how to do it and know what you are doing?  After my initial post in this tutorial, is anything any clearer, or is it actually more confusing?  How do I need to concentrate the next "phase"?