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-   -   What effects Depth of Field (https://www.dvinfo.net/forum/techniques-independent-production/2452-what-effects-depth-field.html)

Charles Papert August 19th, 2002 10:27 PM

I haven't read that issue at length yet, it's kicking around on my desk somewhere. Most DP's like to shoot fairly open, but it does depend on the project. I was fortunate enough to do some Steadicam work for Roger Deakins last month, and was a bit surprised that we were working at an 8/11 stop for a day exterior walk-and-talk...but then figured that it was a definite choice, and came to understand why he would want a deep focus for that particular shot. I like to work that way also, considering what is appropriate for a given shot or mood.

That's for film though. There is no question that video looks better with shallow depth of field, I think it probably has something to do with the rather harsh edges in a video image. The less of them in the shot, while there is still something in sharp focus, the more attractive the image. But unless you are using something like the Mini-35, it's really hard to get DV to fall off in focus at a wide to medium focal length, regardless of how wide open the lens is (and the supplied lenses, while good, are not sharpest at their widest opening).

Istvan Toth August 20th, 2002 02:47 AM

Hi Jeff,

<...Viewing distance also has to be considered. Does the manual state any viewing distances? If not, then their data is incomplete. Viewing distance is usually stated in a distance so many times the diagonal of the screen. My data is in inches, not mm or cm. As an example, a billboard (larger than your typical 35mm screen) looks sharp when viewed from the road. Yet when viewed at a close distance the dots (circles of confusion) are very large and the image is not recognizable....>

The manual calolats first the Hyperfocal Distance for every F.stops and then the "NEAR" AND "FAR" limits for different "Distances from camera to object"

You want me to put the formulas here?
Istvan

Jeff Donald August 20th, 2002 05:38 AM

Depth of field is the distance between the nearest and farthest objects that appear to be in acceptably sharp focus in the image plane. Depth of field involves one image plane and the area between two target planes (in front of the lens).

Depth of Focus is the distance range through which the image of an abject, in a single plane, can be shifted axially and still have the image appear to be sharply defined. This is the area behind the lens, at or near the CCD (film plane).

So, depth of field is a distance, in front of the lens. Approxomately 2/3 of the distance is behind the image plane (subject) and 1/3 the distance is in front of the plane.

I've moved recently and many of my books are still in storeage. I'm sure many would like to see the formulas. Thanks!

Jeff

Istvan Toth August 20th, 2002 12:15 PM

OK, so here is the formula, taken from the "American Cinematographer Manual" 8-th edition, pag:698,699

First the Hyperfocal Distance (definition from the manual: Hyperf.Dist of a lens is that focus setting where objects at infinity and half the focus distance are of an acceptable sharpness)

H= F^2 / (f)(Cc)
F=focal length of lens
f=f-stop number
Cc=circle of confusion

Depth of Field
Near limit
(H)(S) / H+(S-F)

Far limit
(H)(S) / H-(S-F)

Where:
H=HYperfocal distance
S=Distance from camera to object
F=Focal length of lens

Istvan

Hagop Matossian August 31st, 2002 04:56 PM

This forum is addictive!

I have learnt so much from this thread it is hard to beleive. I meant to go out and shoot some gritty night time shots an hour ago and I'm still in my way-too-comfortable desk chair!

thats it! I'm leaving!

Rob Lohman September 2nd, 2002 08:58 AM

Hehe, i can imagine and know what you mean.... Thanks for
the compliment though.


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