i want to is there any rough estimate or calculation using information like focal length and aperture size for depth of field? Certainly not every SLR body are equiped with DOF preview and they may not be useful in low condition. thanks

-- legnum (legnum212@email.com), January 22, 2002

Answers

f-Calc is a good program, but I was trying to get to the website about a day before this question was asked, and the link to the new address seems to be broken. Keep trying it though, because it is worth the download.

-- Brad Hutcheson (bhutcheson@iname.com), January 24, 2002.

There are formulas for DOF. But they are too much to do in one's head to begin with, let alone in the midst of photographing. If you have a programmable pocket calculator like an HP or TI scientific, or Palm computer, a DOF formula could be programmed in. Let us know if you do. I can round up a formula from the Leica Manual or from Arthur Cox.

-- Bob Fleischman (RFXMAIL@prodigy.net), January 22, 2002.

There are plenty of Web pages with calculators, which won't help you much unless you're in the habit of dragging remote Web access with you everywhere you go :-) Some of them give the formula, so you could grab the formula and plug it into a programmable calculator, or print it off and stick it next to a non-programmable scientific calculator and do the calculations fairly easily. I'm pretty sure Bob Atkins has the formula somewhere in the optics section of his Web site (http://www.bobatkins.com/).

But I'm pretty sure there are also DOF calculators available for download to Palm Pilots ... if you have a Palm, you might want to scout around and see what you can find.

-- Steve Dunn (steved@ussinc.com), January 22, 2002.

f/Calc for Palm OS: http://www.tangentsoft.net/fcalc/

-- Jim Strutz (j.strutz@gci.net), January 22, 2002.

There is a method to calculate DOF using mental arithmetic, which is quite easy. Read about it at Harold M. Merklinger's website

If you want a REAL lens calculator that can cope with digital cameras, diopters, extension tubes and teleconvertor (and any combination thereof), try the one that I wrote:
http://members.rogers.com/jul.loke

-- Julian Loke (elan7e-owner@yahoogroups.com), January 22, 2002.

I tried the website Jim offered, but it wouldn't connect for me. The Morgan and Morgan Leica manual gives the following:

Let u = distance of object focused upon;

d = effective diameter of lens aperture;

a = angular size of circle of confusion;

Near DOF limit = u x u tan a/(d + u tan a)

Far DOF limit = u x u tan a/(d-u tan a)

(I wrote u x u for u-squared)

The authors suggest 1/1000 inch for the circle of confusion; however the DOF tables in the Leica manual use 1/30mm, which is 1/750 inch. This calls attention to the arbitrariness of DOF tables and scales.

I'm posting this not because it looks particularly handy, which it doesn't; but because it's what I can lay my hands on at the moment. I will work with it a bit to see if I can get rid of the trig functions by plugging in a specific value of circle of confusion. It must be working, because I'm getting confused already. :<)

-- Bob Fleischman (RFXMAIL@prodigy.net), January 23, 2002.

Okay. I'm baa-ack.

You don't have to worry about using the tangent function. All you need to do is calculate the tangent directly, which you can do just by dividing the circle of confusion by the focal length. Thus:

1/750 inch = .00133 inches.

Assume a 50mm (2 inch) lens

.00133 / 2 = .00067 (this is tan a)

Assume a ten foot focal distance (120 inches):

120 x 120 x .00067 = 9.6

Assume an f/2 lens, 1" diameter:

1 + (120 x .00067) = 1.0804

and the Near limit is 9.6/1.0804= 8.8856 inches closer than 120 inches

and so it is about 111.1 inches.

Now you can do the far limit. It ought to come out about 139 inches, I think. (Just a guess)

Concluding remark: If you can do all this before the sun goes behind a cloud, or your model falls asleep, then it'll work for you. Otherwise just a get a programmable scientific calculator and program it in. Or, get a Leica. the DOF scales on the M lenses are very useable.

Your friend,

-- Bob Fleischman (RFXMAIL@prodigy.net), January 23, 2002.

Make that far limit more like 129 inches.

-- Bob Fleischman (RFXMAIL@prodigy.net), January 24, 2002.