Talk:Hyperfocal distance

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[edit] Question of Definition

Q: Can anyone provide a source for the second definition? I've never heard of it before, and what's more, the difference is NOT subtle, especially as you get tighter apertures and longer lenses. Thanks! Girolamo Savonarola 22:39, 27 April 2006 (UTC)

A: Yes, both definitions are common throughout twentieth-century books on photography and optics. For example, the Manual of Photography, formerly the Ilford Manual of Photography, used the second definition in several editions through Sidney Ray's chapter in the 1978 seventh edition. See these:

  • Ralph E. Jacobson, The Manual of Photography, seventh edition, London: Focal House, 1978; see chapter "The Geometry of Image Formation" by Sidney F. Ray, pp. 80–83.
  • Alan Horder, The Manual of Photography, sixth edition, London: Focal House, 1971.
  • Alan Horder, The Ilford Manual of Photography, fifth edition, Essex: Ilford Ltd, 1958.
  • James Mitchell, The Ilford Manual of Photography, fourth edition, London: Ilford Ltd., 1949.

By the way, in his 1979 book The Photographic Lens, Ray uses both versions, and makes an interesting observation that simplifies DOF calculations to a simple discrete set of easy-to-remember overlapping focus ranges: "When a lens is focused on infinity, the value of Dn is the 'hyperfocal distance' H. When the lens is focused on distance H, the depth of field extends from infinity to H/2.; and when focused on H/3 extends from H/2 to H/4 and so on. This concept simplifies the depth of field equations considerably." This same observation is in Mortimer (1938), Sinclair (1913), and Piper (1901). Sinclair credits Piper with the idea; Piper calls it "consecutive depths of field" and shows how to easily test the idea. Girolamo, I see you've added this observation yourself; it only makes sense to the extent that you accept that the two definitions are approximately equivalent, or if you measure distance from one F.L. in front of the front principal plane.

  • C. Welborne Piper, A First Book of the Lens: An Elementary Treatise on the Action and Use of the Photographic Lens, London: Hazell, Watson, and Viney, Ltd., 1901.

More notes about Piper from my historical studies:

Piper may be the first to have published a clear distinction between "Depth of Field" in the modern sense and "Depth of Definition" in the focal plane, and implies that "Depth of Focus" and "Depth of Distance" are sometimes used for the former. He uses the term "Depth Constant" for H, and measures it from the front principal focus (i. e., he counts one focal length less than the distance from the lens to get the simpler formula), and even introduces the modern term, "This is the maximum depth of field possible, and H + f may be styled the distance of maximum depth of field. If we measure this distance extra-focally it is equal to H, and is sometimes called the hyperfocal distance. The depth constant and the hyperfocal distance are quite distinct, though of the same value." I’m not sure I appreciate the distinction. By Table I in his appendix, he further notes, "If we focus on infinity, the constant is the focal distance of the nearest object in focus. If we focus on an extra-focal distance equal to the constant, we obtain a maximum depth of field from approximately half the constant distance up to infinity. The constant is then the hyper-focal distance."

I have not found the term hyperfocal before Piper, nor hyper-focal which he also used, but he obviously did not claim to coin this descriptor himself.

Johnson 1909 also uses the second definition very explicitly:

"Thus if a lens which is focused for infinity still gives a sharp image for an object at 6 yards, its depth of field is from infinity to 6 yards, every object beyond 6 yards being in focus. This distance (6 yards) is termed the hyperfocal distance of the lens, and any allowable confusion disc depends on the focal length of the lens and on the stop used. If the limit of confusion of half the disc (i.e. e) be taken as 1/100 in., then the hyperfocal distance H = Fd/e, d being the diameter of the stop, ..." I believe he has a factor-of-two error here in using a COC radius instead of diameter.

  • George Lindsay Johnson, Photographic Optics and Colour Photography, London: Ward & Co., 1909.

The better question might be: when did the first definition first get articulated? Dicklyon 00:23, 28 April 2006 (UTC)

ps. I just noticed that I had already put a lot of this info in the history section. See for example what I said about Kingslake 1951, and the nineteenth-century precursors to hyperfocal distance.

The overwhelming comprehensiveness is astounding. Look forward to seeing many of your future edits. One small piece of advice - the article would like a lot cleaner with standard Wikipedia-format footnotes. Also, avoid referring to yourself; this includes your personal research. Sources are what we want. Otherwise, wonderful job. Thanks much! Girolamo Savonarola 20:13, 28 April 2006 (UTC)
Thanks for the comments. I'd appreciate some help with the references, since I'm pretty new at Wiki syntax. Feel free to do it right and I'll follow your lead in the future. As to the comment where I said basically "as far as I know", I didn't see a good alternative under the circumstances. Your change claims that Piper 1901 is "among the earliest" uses of Hyperfocal, but it's hard to know that for sure without a lot more research. Is there a good way to say this is what I've found, without making a firm statement as to what is true? And how can your statement be backed up by a source, if the only source is me? I know this wikipedia is not supposed to be a place to public original research, but where's the line? Dicklyon 20:50, 28 April 2006 (UTC)
By the way, I just noticed that your favorite movie technical reference, Camera Assistant, The: A Complete Professional Handbook by Hart acknowledges both definitions on p.205[1]. And a lot of what is says about depth of focus is really not quite right; see my edits there.

extends from H/2 to H/4 and so on. This concept simplifies the depth of field equations considerably." This same observation is in Mortimer (1938), Sinclair (1913), and Piper (1901). Sinclair credits Piper with the idea; Piper calls it "consecutive depths of field" and shows how to easily test the idea. Girolamo, I see you've added this observation yourself; it only makes sense to the extent that you accept that the two definitions are approximately equivalent, or if you measure distance from one F.L. in front of the front principal plane.

  • C. Welborne Piper, A First Book of the Lens: An Elementary Treatise on the Action and Use of the Photographic Lens, London: Hazell, Watson, and Viney, Ltd., 1901.

More notes about Piper from my historical studies:

Piper may be the first to have published a clear distinction between "Depth of Field" in the modern sense and "Depth of Definition" in the focal plane, and implies that "Depth of Focus" and "Depth of Distance" are sometimes used for the former. He uses the term "Depth Constant" for H, and measures it from the front principal focus (i. e., he counts one focal length less than the distance from the lens to get the simpler formula), and even introduces the modern term, "This is the maximum depth of field possible, and H + f may be styled the distance of maximum depth of field. If we measure this distance extra-focally it is equal to H, and is sometimes called the hyperfocal distance. The depth constant and the hyperfocal distance are quite distinct, though of the same value." I’m not sure I appreciate the distinction. By Table I in his appendix, he further notes, "If we focus on infinity, the constant is the focal distance of the nearest object in focus. If we focus on an extra-focal distance equal to the constant, we obtain a maximum depth of field from approximately half the constant distance up to infinity. The constant is then the hyper-focal distance."

I have not found the term hyperfocal before Piper, nor hyper-focal which he also used, but he obviously did not claim to coin this descriptor himself.

Johnson 1909 also uses the second definition very explicitly:

"Thus if a lens which is focused for infinity still gives a sharp image for an object at 6 yards, its depth of field is from infinity to 6 yards, every object beyond 6 yards being in focus. This distance (6 yards) is termed the hyperfocal distance of the lens, and any allowable confusion disc depends on the focal length of the lens and on the stop used. If the limit of confusion of half the disc (i.e. e) be taken as 1/100 in., then the hyperfocal distance H = Fd/e, d being the diameter of the stop, ..." I believe he has a factor-of-two error here in using a COC radius instead of diameter.

  • George Lindsay Johnson, Photographic Optics and Colour Photography, London: Ward & Co., 1909.

The better question might be: when did the first definition first get articulated? Dicklyon 00:23, 28 April 2006 (UTC)

ps. I just noticed that I had already put a lot of this info in the history section. See for example what I said about Kingslake 1951, and the nineteenth-century precursors to hyperfocal distance.

The overwhelming comprehensiveness is astounding. Look forward to seeing many of your future edits. One small piece of advice - the article would like a lot cleaner with standard Wikipedia-format footnotes. Also, avoid referring to yourself; this includes your personal research. Sources are what we want. Otherwise, wonderful job. Thanks much! Girolamo Savonarola 20:13, 28 April 2006 (UTC)
Thanks for the comments. I'd appreciate some help with the references, since I'm pretty new at Wiki syntax. Feel free to do it right and I'll follow your lead in the future. As to the comment where I said basically "as far as I know", I didn't see a good alternative under the circumstances. Your change claims that Piper 1901 is "among the earliest" uses of Hyperfocal, but it's hard to know that for sure without a lot more research. Is there a good way to say this is what I've found, without making a firm statement as to what is true? And how can your statement be backed up by a source, if the only source is me? I know this wikipedia is not supposed to be a place to public original research, but where's the line? Dicklyon 20:50, 28 April 2006 (UTC)
By the way, I just noticed that your favorite movie technical reference, Camera Assistant, The: A Complete Professional Handbook by Hart acknowledges both definitions on p.205[2]. And a lot of what is says about depth of focus is really not quite right; see my edits there.

[edit] Consecutive depths of field

It would appear that this phenomenon holds only for the approximate formulae for DOF:

D_{\mathrm N} \approx \frac {H s} {H + s}
D_{\mathrm F} \approx \frac {H s} {H - s}

If s = H / a,

D_{\mathrm N} \approx \frac {H (H/a)} {H + H/a} = \frac {H} {a + 1}
D_{\mathrm F} \approx \frac {H (H/a)} {H - H/a} = \frac {H} {a - 1}

This does not work for the “exact” formulae

D_{\mathrm N} = \frac {H s}{H + ( s - f )}
D_{\mathrm F} = \frac {H s}{H - ( s - f )},

so it would seem to break down as the subject distance approaches the lens focal length.

Does Piper shed any light on this? JeffConrad 02:51, 29 August 2006 (UTC)

No, I think he was just working in the approximate regime. I'll look it up again tomorrow; he's at work. You can read the rest of my notes from Piper in my DOF draft paper: [3]. Dicklyon 02:58, 29 August 2006 (UTC)
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