Nature's Children

[Mark]

http://www.karger.com/gazette/64/fernald/art_1_0.htm

[larry cottrill]

Actually a pinhole has a definite and calculable amount of diffraction, with smaller ones diffracting more of the light that goes through them. Everything is equally in focus in a pinhole camera, and everything is equally out of focus because of the diffraction.

Without the diffraction you could use an arbitrarily small pinhole (and a much longer exposure) to get an image of perfect clarity, but in reality you choose the pinhole size based upon the focal length of the camera and other factors.

Diffraction should only be a real problem where you try to use the smallest pinholes you can make. With larger pinholes, you can use more convenient exposure times but the image clarity is degraded by the fact that each point on the object will be represented at the film plane not by a point, but rather by a disk approximating the size of the pinhole (actually somewhat larger). In the camera obscurae of European mansions, the pinhole was almost a "small porthole" and the projected image covered the wall of a small sitting room. (The idea was that you could sit around in the dark and secretly watch what your guests were doing out in the garden or whatever - obviously a source of high amusement.) The image was acceptable because the viewing distance to the wall was several feet, so the image "point" disk size was tolerable. Obviously, it should be possible to calculate an "ideal" pinhole size where the advantage of making the hole smaller to reduce the disk size is cancelled by the increase in size of the diffraction pattern. My guess is, that would be a very small pinhole, requiring long exposures under normal lighting conditions.

Another thing worth investigating (though purists will consider it a "cheat", of course) is the use of a cheap simple lens magnifier behind the pinhole to reduce the image disk size. It would be chosen so that the focal length is just slightly shorter than the pinhole-to-filmplane distance. Such a combination will have almost perfect image clarity combined with the "infinite" depth of field of the pinhole. Even the chromatic aberration of the simple lens is inconsequential because of the constriction of the small "F-stop" provided by the hole.

(Wish I could find a scan of some of my pinhole work.)

I would very much enjoy seeing that. It's really a different kind of photography, because one of your most convenient variables, the F-ratio, is no longer easily manipulated (though it can be calculated if the pinhole size is accurately known).

Ben, do you know how to use a view camera to get an "infinite depth of focus" shot of a building or wall from up close, receding into the distance? The geometry of the solution is amusing - but unfortunately, you can't do it with the kind of cameras we're used to (i.e. with a fixed lens plane and film plane).

EDIT ----------
According to Horace Selby, writing in Amateur Telescope Making, Book III (Scientific American, Inc., 1953, p 473) the central diffraction disk contains 80 percent of the light coming through the aperture and has a diameter = 2 x wavelength x f / D. It happens that the wavelength of yellow light is about 20 millionths of an inch, and of course f/D is nothing more nor less than the denominator of the f-ratio, i.e. the "f-stop number". On page 307 of the same volume, Henry E. Paul makes the interesting statement that "If the focal length of the lens is too long for the aperture (above f/22) diffraction will begin to cause trouble." Of course, he's talking about astrophotography where fine point images are critical. Working it out we see that 2 x 0.00002 inch x 22 = 0.00088 inch or pretty close to 1/1000 inch. This is certainly enough degradation in sharpness to show up if much enlargement of a fine-grain negative is desired, so the f/22 limit seems reasonable.

In the case of a pinhole camera, a point source at a long distance out will project a disk approximately the size of the pinhole, disregarding the diffraction effect just calculated. The diffraction will simply add to the diameter of this disk by spreading the edge of the disk outward all around. Let's (quite arbitrarily) say that the diffraction causes noticeable image degradation if it increases the disk diameter by 25 percent. That means we could have a pinhole as small as 4 x our 0.00088, i.e. 0.0035 without excessively noticeable diffraction effects. Multiplying this by 22 (our limiting F-ratio), we would have a pinhole-to-film-plane distance of a whopping .077 inches, or almost 1/10 inch. So, we could have a pinhole camera that small with imaging that is just noticeably affected by diffraction. Note that this is a very small pinhole to try to make accurately by hand.

If we increase the distance to a more reasonable value, say 7.7 inches, without increasing the pinhole size, the image disk will be overwhelmed by the diffraction effect, since the diffraction is now 100 times greater. What we really want is to find a pinhole-to-film distance f such that the diffraction only blurs the image disk by 25 percent for any pinhole diameter we choose. Since the undiffracted image disk would be the pinhole diameter D, we can say, then, that
2wf/D = .25D OR 2wf/D = D/4
Multiplying both sides by 4:
8wf/D = D
Multiplying both sides by D gives:
8wf = D^2 (where D^2 means "D squared")
We can isolate the "focal length" f by dividing by 8w:
f = D^2 / 8w; since we know that w = 20 millionths of an inch, we can say:
f = D^2 / 0.00016
So, we have a theoretically "ideal" calculation for F if we know how big (or small) a pinhole we can make.

For design purposes, an inversion of this might also be useful so we can design a pinhole for a desired focal length:
D^2 / 0.00016 = f
D^2 = 0.00016f
D = sqrt( .00016f ) = sqrt( .00016 ) x sqrt( f ) = .0126 x sqrt( f ) (where sqrt means "square root of")

(Note that the constants in the above functions are only valid for calculations with all dimensions given in inches.)

Thus, we can design a pinhole camera by deciding how large an ideal image disk we want to allow (this could be determined by film grain size, for example) and using that for D, and then designing for an "ideal" focal length where the diffraction will only impact that disk size by 25%. Alternately, we can decide what "focal length" pinhole we want and determine a hole diameter D that will give the best imaging IF the hole is not too large for the image quality desired (in designing a whole-room camera obscura we might not care that the smallest "point" is a disk half an inch in diameter!).
End of edit ----------

L Cottrill

[Mark]

http://www.karger.com/gazette/64/fernald/fig_2.html

[Mark]

http://www.scienceagogo.com/news/200508 ... _sys.shtml

[Mark]

http://ebiomedia.com/gall/eyes/Images.html

[Mark]

If you have ever seen a time lapse movie of a vast field of sunflowers following/tracking the sun across the sky, it is kind of moving. It's as if they are "watching" the sun.
Mark
http://ebiomedia.com/gall/eyes/plants.html

[Mark]

http://ufbir.ifas.ufl.edu/index.htm

[Mark]

Just a little bunting like the one I saw on a postcard while visiting Bandera, Texas.
Mark
http://www.gdphotography.com/images/1103.jpg

[El-Kablooey]

If you have ever seen a time lapse movie of a vast field of sunflowers following/tracking the sun across the sky, it is kind of moving. It's as if they are "watching" the sun.
Mark
http://ebiomedia.com/gall/eyes/plants.html

I have seen this in real-time on many occasions. There is a small lake nearby that i like to bass fish in. Beside that lake, every year, there is a field of sunflowers covering about 10 acres. I noticed how they did that a long time ago. It really is kind of funny too watch over the course of a day.

[Mark]

If you see them sped up, a day in a minute's time, the heads look alive, like a science fiction plant, they wiggle and twist as if correcting or sensing the best angle; I guess in this way moreso, you can see the life energy that lives inside them, perhaps on the verge of some sort of consciousness. Maybe one day our robots will come to life too, after all, everything is made of matter and matter finds ways to sense itself, if that makes any sense.
Mark

[Mark]

Facing east at sunrise, the sunflower’s head follows the sun across the sky to face west at sunset. This heliotropic movement, called nutation, results from a bending of the stem toward the sunlight; there is asymmetric growth on the shaded side, causing the flowers to be in a position facing toward the sun. Growth is equalized during the night, the stem slowly straightens out and by dawn is facing east again. On a cloudy overcast day, the sunflower remains facing eastward, awaiting the next clear sunrise. The leaves of the sunflower are also heliotropic. If they are removed, the sunflower head would be unable to follow the sun. The sunflower usually reaches maturity three to four months after the emergence of the seedling. As the seeds develop, the heads begin to droop with the added weight and at maturity face nearly downward.

The sunflower is native to North American. It probably originated somewhere in the southwestern part of the land now occupied by the continental United States, in a region including Colorado, New Mexico, Arizona and southern California. Archaeological explorations have come upon wild sunflower remains in Colorado and New Mexico. The American Indian was the first to utilize the sunflower, which was unknown to Europeans until the sixteenth century. Evidence of its cultivation dates from as early as 900 B.C.

Today sunflower seeds are cultivated throughout the world. The main producers are the United States, Russia, and Argentina. Sunflower seeds are also harvested not just for their seeds but for the valuable oil that is made from the seeds. Major advances have been made in plant breeding of sunflowers to develop high yielding, disease-resistant varieties. In 1940, the average oil content of most commercial oilseeds was about thirty three percent. In recent years with the advancement of technology the average oil content can be as high as fifty percent.

Sunflower seeds face many hurdles during growing in the United States. The seeds are considered a delicacy to many birds. Birds act as natural predators to the growing sunflower and often destroy the crops. To make matters worse, major bird feeding takes place around harvest time. To combat this problem, many farmers must use scarecrows, loud noise making devices, or metal strips that glisten in the sun to scare the birds away. Farmers also tend to not plow the fields of earlier crops until after sunflower harvest so the old crop can be used as an alternative feed for the birds.

When sunflower plants reach maturity, most flower heads permanently face east while their backs change color from green to yellow. The head is severed from the stalk and the seeds are removed. Although seed size is largely immaterial for oilseeds, it is an important factor in the non-oil or confectionary sunflower crop. After harvesting and drying, the seeds are cleaned and graded into threw sizes: large, medium, and small. The seeds are then either packed raw, roasted and salted in the shell, or hulled. The medium sized seeds or “hullingâ€

[Mark]

http://sunflower.bio.indiana.edu/%7Erha ... otion.html

[Mark]

http://www.xtmedia.net/eng/e_ivideo.html

[Mark]

http://www.truthorfiction.com/rumors/h/hippo-tort.htm
http://www.snopes.com/photos/animals/hippo.asp

[Mark]

Just a little bunting like the one I saw on a postcard while visiting Bandera, Texas.
Mark
http://www.gdphotography.com/images/1103.jpg

I found this in one of my notebooks, a little tidbit. By the way, the above picture makes a nice screen saver or background for your computer.
Mark