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How to determine depth of field
How can I go about calculating how deep or shallow my depth of field will be at a given aperture? I'm not sure which factors, or combination of, will effect this... focal length, aperture, distance from subject? For instance, if I'm standing 30 meters away from my daughter using a wide open lens at 2.8, using my zoom at say, 80mm... how will I know exactly how deep or shallow my dept of field will be? I sometimes shoot sports/action wide open at 2.8 and the point I focused on will be sharp but other important areas are not. I know experimentaion and adjusting will help me but is there a formular to help one determine this in advance? I appreciate your help!.

Corona_Drinker..

Comments (8)

Press the depth of field preview button. Experience is the only other way...

Comment #1

Use a depth of field calculator such as the one at:.

Http://www.dofmaster.com/dofjs.html..

Comment #2

Corona_drinker wrote:.

How can I go about calculating how deep or shallow my depth of fieldwill be at a given aperture? I'm not sure which factors, orcombination of, will effect this... focal length, aperture, distancefrom subject?.

The items that you listed (and sensor size) all affect DoF..

For instance, if I'm standing 30 meters away from mydaughter using a wide open lens at 2.8, using my zoom at say, 80mm...how will I know exactly how deep or shallow my dept of field will be?.

Like Steve Balcombe mentioned, the easiest way is to use an online DoF calculator. For your example, it would be 17.1m (from 23.7m to 40.8m) on your Nikon D200..

Please note that the DoF calculations are based on standard assumptions (printing an 8x10 and viewing at 10"-12" with normal eyesight for "acceptably" sharp detail). Also, DoF is not a step function, and is a gradual transition. Basically, detail at 23.6m will not be that much different from detail at 23.8m (just a little blurrier, and enough exceed the accepted standard)..

I sometimes shoot sports/action wide open at 2.8 and the point ifocused on will be sharp but other important areas are not. I knowexperimentaion and adjusting will help me but is there a formular tohelp one determine this in advance? I appreciate your help!.

Well, if you are shooting sports, I can assume that you will mostly use telephoto lenses and therefore shoot your subjects at much less then the hyperfocal distance. If that is the case, you only need to worry about f-stop if you keep the subject size the same (focal length and subject distance cancel each other out in the DoF equation)..

See link below for when this rule of thumb fails:.

Http://www.dofmaster.com/dof_imagesize.html.

Note, while it is not mentioned in the link, this rule of thumb can not be used across cameras with different sensor sizes (since DoF is dependent of sensor size). Hope this helps...

Comment #3

For less than Hyperfocal distance, and not macro,.

DoF is proportional to fstop/MagnificationSquared.

Magnification is the ratio of image width to sensor width, so for the same scene composition thru the viewfinder DOF is directly proportional to fstop, regardless of focal length..

Thats because to keep the same composition thru the viewfinder when changing focal length you must also change the distance to the subject which exacty compensates...

Comment #4

Dave Martin wrote:.

For less than Hyperfocal distance, and not macro,.

Not sure what sports can be shot at macro (1:1 magnification) ..

Comment #5

Dave Martin wrote:.

For less than Hyperfocal distance, and not macro,.

DoF is proportional to fstop/MagnificationSquared.

Magnification is the ratio of image width to sensor width, so for thesame scene composition thru the viewfinder DOF is directlyproportional to fstop, regardless of focal length..

Thats because to keep the same composition thru the viewfinder whenchanging focal length you must also change the distance to thesubject which exacty compensates..

The importance of this in the context of sports is that you can easily calculate the depth of field for a desired subject *size*, and that will be (near enough) maintained as the subject distance changes and the photographer zooms to follow the action..

Let us say that you want to follow soccer players who are six feet tall, with a space above and below of two feet - so the players fill the frame with just a little room for cropping. That's ten feet altogether..

Subject distance (ft) / subject height (ft) = focal length (mm) / image (sensor) height (mm)..

Using 100 mm as an arbitrary focal length, and the sensor size of my 400D which is 15 mm:.

Subject distance (ft) = (100/15) * 10 = 66.7 ft..

What we have learned is that a 10 ft high subject at 66.7 ft requires a focal length of 100 mm on the 400D. Ok - now feed this into the DoF calculator:.

400D sensor size100 mmf/2.8Distance 66.7 feet.

Calculated DoF = 6.5 ft in front and 8.1 ft behind - easily enough for soccer, but not too much so we will get good subject isolation from the background..

Now for the key point of all this. As the players move and the photographer zooms to follow the play, *the depth of field remains approximately constant*. So you can make your aperture setting once only then concentrate on the action..

Of course, if you zoom in for a tight head-and-shoulders shot the depth of field changes because the subject framing has changed - but you could pre-calculate that too if you wished...

Comment #6

Dave_s93 wrote:.

Dave Martin wrote:.

For less than Hyperfocal distance, and not macro,.

Not sure what sports can be shot at macro (1:1 magnification) .

Cricket fighting.

Leonard Migliore..

Comment #7

Great example Steve..

Steve Balcombe wrote:.

Dave Martin wrote:.

.....so for thesame scene composition thru the viewfinder DOF is directlyproportional to fstop, regardless of focal length..

The importance of this in the context of sports is that you caneasily calculate the depth of field for a desired subject *size*, andthat will be (near enough) maintained as the subject distance changesand the photographer zooms to follow the action..

Let us say that you want to follow soccer players who are six feettall, with a space above and below of two feet - so the players fillthe frame with just a little room for cropping. That's ten feetaltogether..

......

Now for the key point of all this. As the players move and thephotographer zooms to follow the play, *the depth of field remainsapproximately constant*. So you can make your aperture setting onceonly then concentrate on the action..

Of course, if you zoom in for a tight head-and-shoulders shot thedepth of field changes because the subject framing has changed - butyou could pre-calculate that too if you wished...

Comment #8

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This question was taken from a support group/message board and re-posted here so others can learn from it.

 

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