Depth of Field

IronDogPhoto

Being new to the technical aspects of digital photography, I have a question regarding depth of field.

I recall from my days shooting film, at any aperture/focal the acceptable range of sharpness was considered to be 2/3 in front of the the point of focus and 1/3 beyond the point of focus. In other words, if your total DOF was 3 ft., the acceptable range of sharpness would range from a spot 2 ft in front of the point of focus to a spot 1 ft. beyond the point of focus (distances used for sake of illustration only).

Is this true of digital photography as well, or is there a different "rule" regarding DOF with digital.

For what it's worth, I am shooting a Canon 40D with a 70-200L IS and a 24-70L.

Thanks.

- Gary

JohnBiggs

Actually what I have heard is the oposite. 1/3 in front, 2/3 behind. I believe it to be true. However I don't think this rule changed with digital the optics are still the same.

Thanks,
John

IronDogPhoto

I'm sorry, John. You are right. I got my fronts and behinds switched.

So the same applies to digital, eh? Good to know.

Thanks.

- Gary

JohnBiggs wrote:

Actually what I have heard is the oposite. 1/3 in front, 2/3 behind. I believe it to be true. However I don't think this rule changed with digital the optics are still the same.

Thanks,
John

DoctorIt

Hi Gary - welcome to Dgrin!

Although the digital body is obviously different, optics are optics, and lenses haven't really changed much, at least in basic operation, since the birth of photography. Physics is constant (thank goodness, or I'd need to go back to school every year ). Lenses and other optical components bend, manipulate, and focus light waves the same way, regardless of how the image is captured at the end of the optical path, whether its by burning it into film or registering it in pixels.

jfriend

JohnBiggs wrote:

Actually what I have heard is the oposite. 1/3 in front, 2/3 behind. I believe it to be true. However I don't think this rule changed with digital the optics are still the same.

Thanks,
John

This is one of those "rules of thumb" that is an approximation for some circumstances. It is only perfectly accurate when the subject distance is 1/3 the hyperfocal distance.

The ratio of front to back DOF goes to zero when you get near the hyperfocal distance (because it has infinite depth of field behind the subject so the rear DOF goes to infinity). Similarly, the 1/3 to 2/3 doesn't apply at all a macro focusing distances. Overall, the 1/3 to 2/3 ratio works as an OK rule of thumb as long as you are nowhere near macro focusing distances or the hyperfocal distance.

I found this an interesting read: http://en.wikipedia.org/wiki/Depth_of_field.

pathfinder

This is a great link - http://en.wikipedia.org/wiki/Depth_of_field. -- I have been to this page many times myself.

Well worth a modest perusal.