ROCHESTER INSTITUTE OF TECHNOLOGY
Center for Imaging Science
SIMG 215 - Imaging Science Fundamentals
Laboratory: Pinhole Camera
You will construct and use a pinhole camera, incorporating an aluminum-foil pinhole and a video camera
as the sensor. You will then compare images obtained with different sized pinholes, as well as with images
obtained using a lens instead of a pinhole.
Materials:
Supplied in Lab
Aluminum Foil
“Push Pins”, or needles
Stand Microscope
CCD Video Camera
Imaging Science Workstation, running Photoshop
“eye chart” (letters printed in different sizes)
Apparatus:
A schematic of the pinhole camera is shown below. The diameter of the pinhole is “d”, the
distance from the object to the pinhole is z1 and from the pinhole to the sensor is z2. The sensor is the
charge-coupled device (CCD) in a video camera, which is used without the lens in most of this lab. BE
CAREFUL WHEN USING THE CCD CAMERA -- AVOID PUTTING SHARP OBJECTS (SUCH AS
NEEDLES) NEAR THE SENSOR -- IT MAY BE SCRATCHED EASILY.
Object
Pinhole of diameter "d"
z1
z2
1
Sensor
PROCEDURE
1) Imaging with a lens
Mount the CCD camera on a stand (if not already mounted). Start the program “Photoshop,” set
the file input to “import=>Kodak 323” (the instructor or TA will help with this if necessary) and observe
what happens. The camera includes an electronic circuit that automatically adjusts the amplification
(“gain”) applied to the video signal to maintain an approximately uniform output level.
After getting the best focus (by turning the lens holder, which adjusts the lens-detector distance),
obtain an image of the eye chart, which can be taped or draped over another stand on the optical bench. Try
to get as many letters as possible in the field of view (especially the smallest ones). Measure and record the
height of the smallest letters on the eye chart page that are visible in the image. Save the image to disk (you
may want to create a subdirectory for your team’s images, first).
Now move the camera farther from the eye chart; try to double the distance from camera to eye
chart, if possible. Grab and save another image, centered at about the same spot on the eye chart. Again
measure and record the height of the smallest letters on the eye chart page that are visible in the image.
After you obtain these 2 images, have a lab partner take a picture of you; or, if you wish, the
instructor or TA can take a picture of the whole team. (Consider this image a souvenir of your experience
in SIMG 215.) Save this image. Then remove (unscrew) the lens from the camera. DO NOT MISPLACE
THE LENS or the instructor and TAs will become very angry.
2) Imaging with a pinhole
1. Use the pushpin to make a pinhole as small as possible in the center of a sheet of aluminum foil
about 6" square. Measure the diameter of the pinhole with the stand microscope -- an appropriate diameter
is approximately 1.0 mm (but smaller is better). RECORD the diameter of the hole and note its shape (e.g.
perfectly round; multiple tears; etc).
2. Drape the foil over the lens-less CCD camera, being careful not to tear the foil or disturb the
shape of the pinhole. Use the overhead fluorescent lights or (preferably) a desk lamp as illumination for the
eye chart. Obtain and save an image of the same eye chart as in part (1). Measure and record the height of
the largest letters on the eye chart page that are legible in the image.
3. Now change the distance between the object and light collector (by adjusting the distance of the
camera from the eye chart). Take and save another image. Again measure and record the height of the
largest letters on the eye chart page that are legible in the image.
4. Make a second, larger pinhole in a new sheet of aluminum foil; use more pressure on the
pushpin to ensure that the hole is larger. Measure the diameter of this hole -- it should be of the order of 1.5
– 2.0 mm. RECORD its diameter and note its shape (e.g. perfectly round; multiple tears; etc). Repeat steps
2 and 3 above for roughly the same region of the eye chart. Try to use approximately the same objectpinhole distances (z1) as for the first pinhole.
At the end of the lab, you should have taken and saved (at least) 6 images. These should be ftp’ed or
emailed to each member of your lab group, so they can be included as part of your report (in the
“Observations” section).
Questions/points to consider, to guide writeup:
1.
Use your measurements of the smallest legible letters in your images to make a direct, semiquantitative comparison of the quality of images obtained with the lens and those obtained with
the pinhole camera. Are you surprised, either way, by this comparison?
2.
Compare the images obtained with the different sizes of pinholes for image quality (again, use
your results for the “smallest legible letters”). What factor(s) determine the image quality of a
pinhole camera?
3.
Suppose you weren’t told that the CCD camera circuitry compensates for the amount of light per
second (i.e., the illuminance) incident on the CCD detector. How could you deduce this, by
comparing your images from steps 2 and 4?
4.
How can one control the size of the image formed by a pinhole camera? Specifically: what are two
different ways that you can you could make image size increase or decrease? (Assume you could
control how far the pinhole is from the CCD – which obviously would not be easy given the
present experimental setup -- as well as how far the object is from the pinhole.)
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