D.O.F question

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mintydave

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Dave
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Hi there
as a beginner i have been reading and reading a lot of tutorials to the point of being overwhelmed slightly. So i am taking a different approach and focusing (pardon the pun) on specific topics and at the moment am learing about the apperture. Have got my head round the basics but would like some input on depth of field.

Enough waffle get to the question

Is there a calculation or rough gide to depth of field at approximate appertures. By this i mean if i was shooting at f3.6 would i have an approx dof of "X". I assume there has to be other contributing factors.

as i said im a beginner and have to ask the questions at the risk of sounding daft - but thats what forums are for

cheers
Dave
 
Don't forget to use your DOF button, it's also good at freaking people out with a speedlite :D
 
Someone needs to make a little handheld calculator to carry around with you. I believe theres a app for the iphone, i need one for the blackberry!
 
mintydave said:
Hi there
as a beginner i have been reading and reading a lot of tutorials to the point of being overwhelmed slightly. So i am taking a different approach and focusing (pardon the pun) on specific topics and at the moment am learing about the apperture. Have got my head round the basics but would like some input on depth of field.

Enough waffle get to the question

Is there a calculation or rough gide to depth of field at approximate appertures. By this i mean if i was shooting at f3.6 would i have an approx dof of "X". I assume there has to be other contributing factors.

as i said im a beginner and have to ask the questions at the risk of sounding daft - but thats what forums are for

cheers
Dave
Click to expand...

The DoF Master link is a good one. You will see all the different control parameters there.

There are really only two things that control depth of field. The first and primary control is the f/number as you know.

The other factor is magnification, which needs a bit more explanation. Basically, the bigger the size of the image projected on to the sensor, the less the depth of field. So, if you move closer, the image gets bigger, and depth of field is reduced. Likewise if you fit a longer focal length lens, the image gets bigger and the same thing happens.

Also remember that if you fit a longer lens but then move back so that the image remains the same size as before, depth of field is the same. For this reason, longer lenses do not inherantly produce less DoF than other lenses, as is commonly incorrectly stated. (However, field of view changes with different focal lengths, but that's a different subject.)

The other thing to bear in mind is that depth of field changes with format. If you think about it, it has to because different formats obviously record images at different magnifications. Compacts, with tiny sensors, have lots of DoF, full frame DSLRs with much bigger sensors have much less DoF, and most DSLRs with cropped sensors are somewhere inbetween.

In the DoF Master calculator, the first thing you do is input the particular camera. What you are actually doing here is setting the format size and you will see that this alters the size of the circle of confusion in the bottom right of the panel. (It's the CoC size that goes into the formula, and that's an entire subject unto itself!) Then you input the focal length and distance which then calculates the net magnification, then of course the f/number.

In practise, in a typical picture-taking situation you don't have too many options apart from f/number, so that's the primary DoF control. You can't change the camera, and you've already decided on the framing with subject distance and focal length, so that's also fixed.
 
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