Is the camera obscura a new discovery, and who invented it? The camera obscura has been used for over a thousand years; its origin predates even the invention of optics. The first camera obscura was simply a small hole in one wall of a darkened room or tent. Light passing through the hole formed an inverted (upside down) image of the outside scene on a white screen placed across the room from the hole. The image was dim and fuzzy, but it did accurately show the scenery in full color along with the motion of birds, ocean waves and tree branches swaying in the wind. Artists were undoubtedly the first “users” of the camera obscura, as they soon realized that one could trace on the screen the outlines of buildings, trees, shadows and animals. This rough sketch could later be filled in with color to achieve the artist’s objectives while maintaining correct perspective and sizes for near and distant objects. It seems awkward to view an unsharp and inverted image. Can these problems be solved?
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Transcript
Is the camera obscura a new discovery, and who invented it?
The camera obscura has been used for over a thousand years; its origin predates even the invention of optics. The first
camera obscura was simply a small hole in one wall of a darkened room or tent. Light passing through the hole formed an
inverted (upside down) image of the outside scene on a white screen placed across the room from the hole. The image was
dim and fuzzy, but it did accurately show the scenery in full color along with the motion of birds, ocean waves and tree
branches swaying in the wind.
Artists were undoubtedly the first “users” of the camera obscura, as they soon realized that one could trace on the screen
the outlines of buildings, trees, shadows and animals. This rough sketch could later be filled in with color to achieve the
artist’s objectives while maintaining correct perspective and sizes for near and distant objects.
It seems awkward to view an unsharp and inverted image. Can these problems be solved?
Both difficulties were solved soon after the invention
of optics in the early 1600s. When a lens replaced the hole in the wall it produced across the room an image that was both
brighter and sharper. However, the scene was still upside down. That problem was solved by arranging the lens to look
vertically upward into a flat mirror held at about 45° to the optical axis. Now the image is projected down onto a horizontal
white table where the scene will appear right side up if the viewer stands with his back to the outside area of interest.
Early lenses were single pieces of glass that produced a greatly improved image but one that still suffered from color fringes
around bright objects an increasing unsharpness° toward the edge of the viewing table. A camera obscura today uses a lens
with two or more glass elements that reduce these problems.
Four hundred years ago, the flat mirror was simply a polished metal plate. About 1850, opticians learned how to apply a
shiny silver film to a polished flat piece of glass, thereby producing a flatter mirror of much higher reflectivity. Today, most
flat mirrors are made by evaporating a film of aluminum onto a polished glass plate. This technique makes a much more
durable reflecting surface.
How can I make a simple camera obscura?
Such a basic device is often called a pinhole camera. It is made by cutting a ½ inch hole in one end of a light-tight cardboard
box and placing a white paper viewing screen on the opposite side of the box. The imaging pinhole is made in a small piece
of aluminum foil that is taped in place over the ½ inch hole.
The pinhole is made in the foil with a needle to produce a clean, sharp hole with a diameter of about 1/100th of the distance
from the hole to the screen. For example, if that distance is 10 inches, the pinhole should be about 1/10th of an inch in
diameter. Larger pinholes make a brighter but fuzzier image, while because of optical effects, a smaller pinhole also yields a
less sharp image.
The image on the white screen may be viewed by mounting the white screen over the hole cut in the side of the box. In this
case you view the inverted image through the backside of the white screen. Another arrangement uses a small hole cut in
the side of the box that is carefully shielded to keep out stray light yet allow the viewer to see the screen.
How can I make a brighter and sharper image than I get with a pinhole camera?
A better image is made by replacing the pinhole with a lens whose focal length is equal to the distance from the lens to the
viewing screen. The diameter of the lens might be ½ to 1 inch for a focal length of 10 inches. In a basic instrument this can
be a simple lens made of one lens element. Such lenses are available from the Edmund Optics Company
(www.edmundoptics.com).
Remember, both the pinhole and the lens produce an inverted image.
The pinhole camera is nice, but how can I make an imagethat shows more detail and appears right side up?
To achieve these improvements you must make a much bigger camera obscura in which the viewer sits inside the
instrument. Such a device uses a larger lens of longer focal length and also includes a flat mirror mounted above the lens.
The viewers now sit or stand inside the darkened room to see the image on a horizontal white table. Those viewers with
their back to the scene of interest will see a right side up image.
The smallest such instrument suitable for a single viewer might use a lens of 40 or 50-inch focal length. This device would
display details in the scene 4 or 5 times larger than produced by the 10-inch instrument described above. Larger lenses with
even longer focal length can reveal surprising features of very distant objects. For instance, a lens of 100 inches focal length
will show an image of the full moon that is about 1 inch in diameter. Such a view is like looking at the scene with a 10 power
binocular. The largest camera obscuras today use lenses of 12 to 14 inches diameter and produce focal lengths of 250 to
350 inches.
Large instruments are usually equipped with electric motors to carefully rotate the flat mirror about the vertical axis (azimuth)
and to tilt the mirror to shift the view upwards or downwards (altitude). Many camera obscuras also provide means to move
the lens vertically over several inches to focus the instrument on near or distant objects.
As the focal length of the lens is increased, the lens diameter must also be made larger in order to maintain adequate image
brightness. The ratio of lens focal length to diameter is called the speed or f/number of the lens; this ratio determines the
brightness of the scene on the table. This brightness is proportional to the square of the f/number. For example, the image
produced by an f/8 lens is four times brighter than that made by an f/16 lens. Most camera obscuras use lenses of f/15 to
f/30. Note that the apparent image brightness is strongly affected by stray light; the viewing room must be as near to total
darkness as possible.
Can I expect to view astronomical objects throughthe camera obscura?
Most camera obscuras are arranged to view the surrounding landscape of buildings, mountains, a coastline or a harbor
scene. These views occasionally will include a dramatic sunset or moonrise and indeed, such a scene can be especially
dramatic. Observers must use great care in looking toward the sun, as even a reddened sun near the horizon can easily
cause serious eye damage or blindness if viewed directly. The solar image on the view table may be dazzling but it will not
cause permanent eye damage.
The instrument can be specially designed to see the moon and bright planets even when 30° or 40° above the horizon. Such
a camera obscura must include a flat mirror that is significantly larger than normal. A conventional camera obscura uses a
flat mirror that is an inch or two wider than the lens diameter and also about 1.5 times longer than its width. The difference
between length and width is cause by the need to place the mirror at 45° to the lens optical axis. For example, a lens of 6-
inch diameter would require a flat mirror of about 7x10 inches.
If the camera obscura is to view objects higher in the sky it must use a flat mirror of the standard width but with up to twice
the usual length. Such a flat will be much more expensive than a normal mirror.
The Sky in a RoomGiorgio Carboni, May 1996
English version revised by Ed Vogel
CONTENTS
IntroductionThe main component: the converging lensLens on a windowLens on a wooden boardLens on a roll shutterConclusion
INTRODUCTION
This time, we will deal with an optical experiment easy to do, but which, in spite of its simplicity, is able to give you a continuous marvel. What you have to do is simply mount a lens on the bedroom window. In this way, when you wake up in the morning, you will admire the outside scene projected on a wall of your bedroom (figure 1).
If your window is turned to East, you will be able to enjoy the spectacle of dawn and the sunrise. This show changes every day, according to the seasons and the weather conditions, and you will never become tired of observing it. During a storm, lighting will seem to fall in your room. If you live in a City, during the night, you will see car lights to chase each other; the building in front of your house, open one eye or the other; you will see street lamps far away. Some nights, if you have the window facing the favorable direction, you will see the Moon run among the clouds.
For centuries, people experienced the observation of the world behind closed windows. If a knot in the wood of which the window was made just fell, the image of the outside world was formed on the opposite wall. This image is formed because light travels in straight lines. Hence, the rays coming from every object, passing through a thin hole, will attain distinct points on the wall. Those which are coming from a lower point, passing through the hole, will reach a high position on the wall, and vice versa. For this reason, the images produced are inverted.
The optical principle on which this experiment is based is that of the lens which creates images. You can read how this lens works in the section "From Lenses to Optical Instruments" of this Gallery.
This experiment is suitable also to explain the concept of camera obscura and how man has gone from the camera obscura to the photographic camera. The camera obscura is simply a dark room, which can have dimension ranging from many meters to a few centimeters. With a simple hole in a window, an image of the external world will be formed
on the opposite wall. Usually, this image is faint. To increase its brightness, you should enlarge the hole. Unfortunately, in doing so, the image becomes more confused. In order to obtain a brighter and a clearer image at the end of the XVI century, G.B. Della Porta suggested the use of a lens. Many artists of the renaissance used this system to draft their views. This method was particularly useful in taking architectural scenes, with the correct perspective.
For long time, people looked for chemical compounds sensible to the light to the aim of allowing the light draw the images by itself. The photographic camera born as a consequence of the success in these attempts. In fact, the photographic camera can be considered a camera obscura with a film: a surface sensible to the light, able to record it.
THE MAIN COMPONENT: THE CONVERGING LENS
Now, let's to see how you can make the experiment of the camera obscura, which will allow you to enjoy having the sky in your room and, in some manner, your soul outside. Its main component is a converging lens with a focal length about equal to the distance between the lens and the wall where the image is formed. Usually, this value will be comprised between 4 and 5 meters. You can buy the lens at the optician's. A meniscus lens for eyeglass, and as cheap as possible, is good.
Unlike all the people in the optics field, the eyeglass industry is the only one that measures focal lengths as diopters. So, when you go to the optician to buy the lens for this experiment, he will ask you how much power, or diopters, you want it. This simple formula allows you to pass from the focal length to the diopters:
D = 1/FL
where: D = dioptersFL = focal length of the lens (expressed in meters!)Besides, people place the sign "+" before the power of a converging lens and the sign "-" before the power of a diverging lens. For this experiment you need a converging lens.
Let's make a couple of examples:- a converging lens of half a meter of focal length has a power of +2 diopters. In fact: D = 1/0,5 = +2
- a converging lens of 4 meter of focal length has a power of +0.25 diopters. In fact: D = 1/4 = +0,25
You cannot find in the market lenses of every value of focal length, but only of fixed values of 1/4 of diopter, so: +0.25 +0.5 +0.75 +1, etc. With difficulty you will be able to find in the market values such as +0.2 or +0.3 diopters which could be handy for you. In any case, ask to the optician for the lens of the theoretical power you need. It is his task to look for the one closer to the ideal measure. To this purpose, it is better to have a focal length shorter than the room width rather than longer. So, at least the objects close to the window could correctly focus on the wall. In terms of diopters, a slightly more powerful lens is better than a less powerful one.
Ask the optician to reduce the lens diameter so that it can settle down precisely in the bottom of a 24x36 film container, as shown in figure 2. This work is commonly performed by opticians to fit lenses into eyeglass frames, therefore do not be afraid to ask that to the optician. After this operation, make a case for your lens as that shown in figure 2. According to the type of window you have, you can mount the lens in different ways, some of which can be permanent, other temporary.
The mentioned below company produces lenses on demand. You can order one or more lenses with the diameter and focal length you need. As the price of one lens doesn't differ greatly from that of more, buy a few of them in order to have them in reserve.SILO SRL Via di Castelpulci 14/D - Badia a Settimo 50018 Scandicci (FI) [email protected] - http://www.silo.it Lenses and other optical items.
LENS ON A WINDOW
Usually, in USA, houses have windows glasses sliding along the vertical direction. Outdoor light is attenuated by curtains and the room is not completely darkened. In order to make our experiment, it is necessary apply to these windows an opaque roll shutter which entirely halt the light. In fact, light must pass through the lens only. To this purpose, the shutter has to be fully opaque, and it must slide along two lateral guides. In commerce, you can find a shutter of this kind and you have only to saw it to the right width and then insert it in the window opening as shown in figure 3. If you do not find this type of shutter, you can buy an anti-mosquito roller web, and to replace the web with a black plasticized tissue, or a black plastic strong film.
After mounting the lens in its case, you have to insert it in the hole of the lens holder which you have to fasten to the window (fig. 3). When you will have inserted the shutter on the window opening, you must open a hole in the tissue in order to
allow light entering the room. Take care to close every other light source, otherwise your faint image will lose contrast.
This method is easy to perform, and allows you readily open the window to aerate the bedroom during the day.
LENS ON A WOODEN BOARD
In some other countries, the houses are constructed with heavy rolling shutter already fitted onto the windows. Usually, these shutters are made of wooden or plastic slats, which are hooked each other and slide along two lateral guides. When these shutters are completely down, never a light ray is entering the room. In this case, you can mount the lens in two manners: a temporary one and a permanentone.
The temporary solution involves mounting the case with the lens in a hole made in a wooden board. Place the board on the window-sill and pull down the shutter as you can see in figure 4. Take care of not let light to filter among the slats. As the board must be shorter than the windows width in order to be put in place, you have to close the remaining opening also.
Permanent solution requires the authorization of your wife: a thing not easy to obtain! The question is to make a hole in a slat in order to insert the case with the lens in it. Figure 5 indicates how carry out this hole and fit the case in it. The plastic slats have two walls, one inside, the other outside. So, you have to make two coaxial holes of different diameter (fig. 5). You can easily make the internal hole with an annular drill. You can do the external hole with a circular path of little holes, removing the central part, and finishing with a half-round file. When you finish working the hole, place some glue and insert the lens case into the slat.
I have been successful in obtaining from my wife the authorization of making the hole in my shutter, and I have been very glad of this solution. From an aesthetical point of view, the work is not nasty to see and even my wife has not grumbled. The shutter works as usually, carrying and rolling the lens without any problem.
The solid corner of the light yielded by the lens is near 180°. This means that it will project the image on every wall of the room, floor and ceiling comprised. The only wall excluded is that of the window. Any way, the image will be distinct only on the wall opposite to the window. The other walls will send reflected light which will lower the contrast of the principal image. To get round this problem, at about 10 cm of distance from the lens, apply a mask with a rectangular hole. In my case, as the glass of my window is at this distance, I have been able to mount this mask directly on it. In doing so, I used an adhesive sheet of black plastic. This mask is useful also to stop the light which otherwise would arrive on your eyes when you are sleeping.
CONCLUSION
Every morning, when I wake up, I see in my bedroom the panorama of the external world. I know if there is the Sun, or if the sky is cloudy. Not only, but I watch also people walking in the park and trees swaying in the wind.
To have the external world inside your room, even only as an image, will improve remarkably the sleep quality because you feel yourself in some way out of the room and that will give you a great sense of freedom. As that fine song said: "The room has not more walls...". I think that this experiment has also a therapeutic capability for many people who are depressed or who have sleeping problems. However, pay attention when you are sleeping, because if the Moon disk should lie on your skin during a night of full Moon, you could be enraptured in a fantastic dream.
Building Information
'Amazing Camera Obscura' was born of an enthusiastic interest in Camera Obscura.
Over the last six years, showing and building Camera Obscura, we have gained experience that we can make available to all.
Our background in construction, specializing in traditional flintwork, means we have the skills necessary to build a Camera Obscura from the ground up. Alternatively it is possible to install optics into an existing building, be it a garden summer-house or a top floor room. We are also happy to work in
conjunction with designers and architects on new projects.
Site visits can be arranged via our contacts page.
Northampton Camera Obscura:
After hosting a talk on pinhole photography as part of the Pin:Whole exhibition at Essex University, Photographer Gina Glover saw our mobile booth Camera Obscura and contacted us with a view to turning an old summerhouse into a Camera Obscura.
Having visited the site to confirm the strength and suitability of the structure the design stage got underway. We decided to raise the viewpoint by mounting the optics in a tower on top of the summerhouse. Being a summerhouse it was endowed with a large number of windows, which we would deal with by means of wooden
Once the designs were agreed upon we contacted our optics supplier to have them start making the lens to our requirements. Meanwhile we began to build the tower, turning gear and the viewing table in our Sussex workshop.
During the week preceding Easter we travelled up to Northamptonshire and began to convert the summerhouse. We started by strengthening the structure internally to accept the weight of the new tower. We then proceeded to cut a hole in the roof over which we put the tower. Once in position the turning gear and optics were installed. The Camera Obscura was not useable at this stage because of the enormous amount of light flooding in through the windows so we set about making the shutters. The viewing table - a semi-spherical dish - was given vertical movement to enable it to focus equally well on things both near and far.
Gina Glover told us:
"As someone who makes pinhole photography I am interested in the special qualities of image that the device produces. Everyone who has seen it finds the effect enchanting and say they have seen nothing like it. When you observe the images in the complete dark of the summerhouse, you feel like you are flying above the grounds of the house."
Making Your Own Camera Obscura
Simple camera obscura can be made in the following ways.
Room Camera Obscura
Open cardboard boxes out flat, and then use them to black out the windows in a room by pinning or taping them around the window frame. The room must be completely dark as any light coming in will ruin the image, use some tape to cover any small chinks of light. Next make a hole in one of the cardboard blackouts using a pencil, this will then project an image on to the opposite wall - hang up a white sheet if the wall is a dark colour. The image will be very dim, and it may take a few minutes before your eyes will adjust to the low light levels and the image becomes visible. A larger hole will let more light through, but will make for a more blurry image - experiment with the hole size until you reach a compromise between sharpness and brightness.
A large hole will make the image more blurry - that is unless you put a lens in the hole. A cheap lens can be purchased from any opticians with their own lab, prices vary from shop to shop.
Opticians measure the focal length of a lens in Dioptres. The lens must be a converging lens which opticians denote with a +.
For our purposes the focal length is the distance between the hole and the wall. If the wall is 2m away then the dioptre value will be 1 divided by the distance 2m which is ½ or +0.5 Dioptres. For 4m it will be 1 divided by 4m which is ¼ or +0.25 Dioptres.Cut a hole of a suitable size for the lens and fix it in place with tape. This will give you a brighter image.
8. Look at screen through tube, slide the Screen Tube in and out of Lens Tube to focus the image.
Lenses can be used but due to fixed focal length, camera size needs to relate directly to the focal length of the lens being used. Here is an opportunity for
experimentation.
1676
Johann Sturm (Germany) described first known use of a reflex mirror in a camera obscura.[14][15][16][17] The camera obscura
was known to Aristotle as an aid in observing solar eclipses, but its use as an artist's aid was first expounded
by Giambattista della Porta (Italy) in 1558.[18][19] The reflex mirror corrected the up-down image reversal that could make
using a non-SLR camera obscura disconcerting – but not the left-right reversal.
1685
Johann Zahn (Germany) developed a portable SLR camera obscura with focusable lens, adjustable aperture and
translucent viewing screen. These are all the core elements in a modern SLR photographic camera – except for an image
capture medium.[20][21][22] It would not be until 1826/27 before Joseph Nicéphore Niépce (France) made the first permanent
photograph using a bitumen photosensitized pewter plate in a non-SLR camera.[23][24] All advances in photographic
Olympus Evolt E-330 (Japan): first live view digital SLR. Had a secondary CCD sensor to send a live video feed to a
swiveling 2.5-inch (64 mm) color LCD panel (normally used for camera function data) and allow its use as an auxiliary
viewfinder when the photographer's eye cannot be at the SLR viewfinder eyepiece. A sharper live view mode was
available that temporarily flipped aside the reflex mirror (blacking out the primary porro-mirror SLR viewfinder) and opened
the shutter to send a live feed from the primary 2352×3136 pixel (7.5 MP) Four Thirds format MOS image sensor.[707] Most
new for 2008 digital SLRs had a live view mode.[708] Although today live view has limitations (unintelligibility in bright
sunlight, image lag with moving subjects, rapid battery drain, etc.), its perfection, plus an electronic shutter, would make
the bulky and expensive precision mechanisms and optics of a focal-plane shutter, instant return mirror and pentaprism
unnecessary and allow the camera to be a completely electronic device. (This has already occurred with snapshot
cameras – the vast majority of point-and-shoot digital cameras lack an optical viewfinder.) In other words, the Micro Four
Thirds format Panasonic LUMIX DMC-G1 (Japan, 2008) mirror-less non-SLR, interchangeable lens digital camera with
high resolution electronic live view viewfinder and LCD[709] might be the first of a new breed of camera with the potential to
end the history of the single-lens reflex camera.[710][711][712][713][714][715]
Nikon D90 (Japan): first digital SLR with high definition video recording capability. Had 12.3 MP APS-sized CMOS sensor
with secondary 1280×720 pixel (720p), 24 frames per second HD video capture with monaural sound for five minutes in
September.[716][717][718][719] Two months later, the Canon EOS 5D Mark II (Japan) 21.1MP full-frame CMOS D-SLR came out
with 1920×1080 pixel (1080p), 30 frame/s HD video with monaural sound (stereo with external microphone) for twelve
minutes.[720][721][722][723] The D90 and 5D II are otherwise straightforward 2008 D-SLRs. Point-and-shoot digital cameras have
had video recording (usually standard definition, but HD recently) for a few years and it is expected that HD video
recording will soon become a standard D-SLR feature.[724]
Sony SLT α33 and SLT α55 (Japan): first SLRs without an optical viewfinder. What appears to be a pentaprism head is a
high resolution electronic viewfinder (EVF). Had 16.2 MP (α55) or 14.2 MP (α33) APS-sized CMOS sensors with
secondary 1080i high definition video capture. Also had a swiveling live view LCD panel. The SLTs' fixed so-called
"Translucent Mirror Technology" reflex mirrors (a revival of pellicle mirrors [see Canon Pellix above]) siphon off light to
their fifteen phase comparison autofocus sensors to provide continuous autofocusing in their HD video mode.[725] [726] [727]
Camera ObscuraThe earliest cameras obscura used only a pinhole, so that the location of the back wall was not critical. They date back to at least 350 BC. The main problem is that the image is very dim for decent resolution. The smallest detail that can be resolved is the diameter of the pinhole.
In order to get useful brightness, a lens must be used. Here another problem crops up--the focal length needs to be equal to the distance from the wall with the lens to the back imaging surface (just as in any "camera"). One can make a simple, long focal length lens by combining a negative and positive lens. For example, a +2.5 diopter (0.4meter focal length) positive lens combined with a -2.0 diopter negative lens will yield a +0.5 diopter power, or a 2 meter focal length.
A panel of foamcore or similar white material placed 2 meters from a blackened window with this example lens in it should provide a good viewing surface. Black plastic sheeting used for protection of floors when painting is pretty opaque, and is good for blacking out windows.
Be prepared for dim images. Suppose the lens diameter in the example is 25mm, yielding an f/no. of f/80. The "brightness" of the image on the screen will be: B(i) = R* B(s)/(4*f^2) where R = Reflectance of the image board (approx. 0.8)B(i) = image brightnessB(s) = scene brightnessf = lens f/no (80 in the example)
For this case, then, the image will be 32,000 times dimmer than the outside world. If the outside is reflecting an average of 3x10^4 lumens/m^2 (midday bright sunlight), about 1 lumen/m^2 will be reflected from the white panel. This is about 10 times the apparent brightness of a scene lit by the full moon at zenith.
The advantages of a small room (camera) are obvious from the equation. The image brightness will increase by a factor of 4 if the dimension is reduced to 1 meter, or decrease by a factor of 4 if the dimension is increased to 4 meters. If you can find a larger aperture lens, the brightness will also benefit by the square of the lens diameter.
ReferencesGernsheim & Gernsheim "the History of Photography" (Oxford University Press; 1955) - Part I contains some historical material on the camera obscura.
John H. Hammond "The Camera Obscura" (Adam Hilger, Bristol; 1981) - a nice little book on the history and existing camera obscura for public viewing in about 1980.
Book three of the series "Amateur Telescope Making" (1956) has a couple of pages on what they call a camera oabcura, (which is sort of a large view camera) but describes the use of a simple meniscus lens with a stop in front of it (described as a
rear landscape lens). The relatively wide field of view of the landscape configuration is a plus in this application.