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so... i was chatting with al the other nite on irc about putting together a depth of field calculator. being the software geek that i am, i told him i'd be more than happy to write one. it piqued my interest enough to start reading a bit more about something that i knew nothing about.

however, several questions are looming. calculating the hyperfocal distance is all well and good for understanding where your point of focus needs to be to get sharp depth of field. now, with all of our fancy electronic cameras with the af, 45 points of eye controlled focus, built in metering, etc, how do we know that the hyperfocal is correct? none of the lenses i have for my canon have focus marks on them. is the camera calculating the hyperfocal and focusing on the correct spot? is the depth of field preview button calculating that? or do the focus points calculate it? or do the focus points just tweak the laws of physics to make it all work?

i'll probly break out the 30yr old minolta my father-in-law gave me this wknd and give it a whirl on manual. my luck i'll get the hyperfocal right on but i'll munge the f-stop and shutter speed so badly that nothing will come out so i'll never actually know.

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sean

Sean,

There's some interesting hyperfocal stuff here:

http://www.outsight.com/hyperfocal.html

Aside from that, I can't answer any of your questions, Luddite that I am. All of my gear is totally manual.

This is also discussed in another thread on this site at:

http://www.usefilm.com/forums.php?forum=1&topic=107

I agree, even high-end zooms seem to miss this feature.

You can find plenty of information about hyperfocal distance (HD), depth of field (DOF), and the equations for calculation of both with a search on the internet.

The concept of HD is based on the thin-lens equation. This is an approximation of how lenses focus (with the assumption of a single element lens that has no thickness.) When applied to real-world lenses, the thin-lens equation is a reasonable approximation, but is not exact.

There are some reasons why modern lenses don't have the DOF scales. First, it is rather difficult to put a DOF scale on a zoom lens because the HD changes with focal length. Although, you can find one-touch zooms (the kind where the barrel slides forward to zoom) with scales. Second, on modern autofocus lenses, the amount of rotation needed to change focus from infinity to, say, 5 feet, is small, to enable fast autofocus. On these lenses, the DOF scale would be too small to be useful.

So, to use HD with modern lenses, you often just estimate the distance to the nearest object you want to be in focus. Two times that distance is the hyperfocal distance you want. For a given focal length, you can then look up the HD in a table. Focus at the HD to get everything from the near object to infinity in focus.

I find that I use the scales more for zone focusing. I usually want to know what will be in focus in front of and behind the subject of a photo. For example, if I focus on the eyes of a person, I like to know if the tip of the nose will be in focus when I use a 100mm lens at ten feet. DOF scales are handy for these calculations.

I like the elegance of the DOF scale on a lens. A very simple tool that allows quick, reasonable calculations of DOF. After lamenting the lack of DOF scales on my lenses, I wrote a program for Windows to print DOF calculators I could use in the field. The calculators work the same way the DOF scale on a lens works. The program will print calculators for any focal length and any format (digital, 35mm, medium-format, and large-format.) You can also use the calculators on the screen by clicking and dragging the scales.

The program is free at http://dfleming.ameranet.com/custom.html

The attached picture shows a DOF calculator glued to a 58mm lens cap. Other examples are shown on the web site.

In the course of research on the subject of hyperfocal distance and depth of field, I found some discussion on the topic from over 60 years ago.

American Photography, August 1938, pg. 602: "H.F.M., Oakland, Calif., writes that he has been told that we can furnish him with a depth of focus chart for his 9 by 12 cm camera."

American Photography, September 1937, pg. 683: "K.H.S., Easton, Pa. writes: there seems to be a good deal of confusion concerning the question of depth of focus in relation to the circle of least confusion. A clear discussion of this subject would be greatly welcomed."

I noticed that prior to WWII, none of the lenses pictured in the magazines had depth of field scales. During the period from 1938 to 1940, American Photography magazine had no fewer than 6 articles and answers to reader questions explaining hyperfocal distance and depth of focus (what we now call depth of field.)

By 1955, it was common to see the depth of field scales on lenses. In a couple of ads for cameras, the depth of field scale was mentioned as a feature. But, as the scales became commonly available, articles on the topic became scarce. I didn't find any articles on the topic in 1954 and 1955.

Interestingly, an article in the February 1940 issue of American Photography, "The Construction of a Depth of Focus Calculator" describes a method for drawing circular slide rules. Although I developed the method independently, the method described in the article is almost identical to that used in the program described above.

wow. thanx for all the info don. the absence of markings on the lenses makes more sense now. i'll take a peek around your site.

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Jan S.	Danny B.	Gustavo S.	Riny K.	Radovan M.	Alfons R.	rahim y.	Jan S.

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