A much simpler formula is: H = 1000 * D, where H is Hyperfocal-distance, and D is diameter-of-the-aperture. (1000 * D assumes an 8x10, or 8x12 print regardless of the format.)
You can determine D from: D = f / N, where
f is focal-length, and
N is f-stop.
(Note: f and N are used only to determine the aperture. They have no direct affect on DOF or H.)
DOF can be determined from: Dn = H * Ds / H + Ds, and Df = H * Ds / H - Ds, Where Ds is subject-distance (or focus-point), Dn is near-distance, Df is far-distance.
Advanced cameras usually have a DOF scale based upon an 8x10 print, thus these formulas have direct application. Many snapshot cameras used 5x7 since they are less likely to have large prints made. You can simply change the f-stop opening up one stop for 5x7 and two stops for 4x6 prints. Normally you do not have to close down for larger images because they are intended to be viewed from farther away.
ZONE FOCUS is nothing more than setting the camera so that the anticipated action is within the DOF range. In other words some place between Dn & Df. Then to take the photo you do not have to adjust the focus when shooting.
As others have mentioned you can simply use the DOF scales on your lens, if it has them, some zooms do not. Otherwise a table generated from the above tables will work very well.
--
Jens Bladt wrote:
Hyperfocal distance (H) is a way to dertemine the distance to focus the lens for a given aperture and focal length to ensure maksimum DOF, when you want sharpness to infinity (e.i. landscape photograph):
H = FxF/fc F being Focal length f being f-number (aperture) c being the diameter of Circle of Confusion (CoC could be 0.021mm for 35mm negs enlarged to a 8x10 print).
At 70mm lens f8 "H" would be (35mm neg): 70x70/8x0.021 = 29167 mm = 29.2 meter
This means, that if you set the distance to 29.2m, you will get sharpness (on a 8x10 inch print) from infinity to as close as you can get at f 1:8
If you are a landcape photographer, you should have a table in your camera bag giving "H" for the most used focal lengths at let's say f22 or 32.
At f22 the math should be: "H" = 70x70/22x0.021mm = 10.6 meter The near limit of sharp focus is:
Fu(F+cf)/FxF+ufc (u being the used distance in mm)
70X10606(70+22x0.021)/70x70+10606x70x0.021)= 5338mm = 5.3m. The image (8x10) will appear sharp from 5.3m to infinity at f22 when focus distance is set to 10.6m Source: Andrew Hawkins & Dennis Avon; "Photography", UK 1979.
all the best
Jens Bladt
mailto:[EMAIL PROTECTED] http://hjem.get2net.dk/bladt
-----Oprindelig meddelelse----- Fra: Doug Franklin [mailto:[EMAIL PROTECTED] Sendt: 9. april 2004 06:33 Til: [EMAIL PROTECTED] Emne: Re: Zone Focus - what is it?
On Fri, 9 Apr 2004 07:25:27 +0200, Boris Liberman wrote:
Please enlighten the ignorant, as usual...
Using the hyperfocal distance of the lens, possibly modified, to make sure that everything you're likely to shoot is in focus. For example, take your lens and figure out what f-stop you want to use. The turn the focus ring until the infinity mark lines up with the "tic mark" for the f-stop you're using. The "tic mark" on the other side of center will tell you what's going to be in focus. So, just to pull some numbers out of thin air, you pick f/5.6. When you line up the infinity mark on the focus ring with the "5.6" tic on the barrel you might find that the opposite tic indicates 10m. That means everything from 10m to infinity will be in focus. So you don't worry about focusing unless the target is closer than 10m. You can shift it closer if you're not worried about things at "infinity" distance.
TTYL, DougF KG4LMZ
-- graywolf http://graywolfphoto.com/graywolf.html
