AstroMedia 419.COB Instrukcje budowania - Strona 11
Przeglądaj online lub pobierz pdf Instrukcje budowania dla Zabawka AstroMedia 419.COB. AstroMedia 419.COB 12 stron. Camera obscura
Drukuj stronęTips for using the camera obscura:
Tip 1
Make sure that the subject is well lit and that
the camera obscura itself, especially the tracing pa-
per screen, is in the shade or in the dark.
Tip 2
You can see the picture more clearly by cov-
ering yourself and the screen with a dark cloth or a
piece of clothing.
Tip 3
If the inner lens tube moves too easily, you can
glue some strips of (black) paper into the outer tube
to make the fit tighter.
Tip 4
Unwanted reflections, which cannot be avoid-
ed despite the black inner walls, can be greatly re-
duced with the additional diaphragm provided. Cut
it out of the cardboard and fold the eight tabs back-
wards. Push the diaphragm, octagon first, into the
open end of the inner lens tube, opposite the lens,
until the tabs are flush with the edge of the tube.
You can secure it in this position with a few drops of
glue or, if you want to experiment with other dia-
phragm sizes, just leave it loose.
Tip 5
The lens has a large aperture and with a focal
ratio of 4.8 a high light intensity. The focal ratio or
f-number is calculated by dividing the focal length
of 275mm by the 57mm lens diameter. A trade-off
for the bright picture is the low depth of field, i.e.
only objects that are at a similar distance are imaged
sharply. By moving the lens in or out you can adjust
the camera to different distances. You can increase
the depth of field by reducing the lens aperture with
a diaphragm made from dark cardboard. The small-
er the diaphragm, the larger the depth of field and
the dimmer the image will be.
Tip 6
The lens cannot be pulled out far enough for
very close objects. However, you can get around this
with a makeshift extension made of black paper,
which you fold into a suitable octagonal tube and
insert between the inner and outer lens tubes.
Photo prints of your drawings
The camera obscura is not suitable for direct exposure
of photographic paper, but you can make very impres-
sive photographic prints from pencil drawings you made
on the tracing paper. There is a simple method without
having to use a darkroom or chemical developers. Take
a sheet of AstroMedia's Solar Photo Paper (article No.
411.FSP) and place the front side of the sketch, which
is mirror-inverted, on the photo paper when exposing.
When developing (with normal tap water!), a white neg-
ative appears on a dark blue background, now showing a
right-sided image.
The Camera Obscura as a pinhole camera
Your Camera Obscura can also be turned into a pinhole
camera. To do this, remove the inner tube with the lens
and cover the outer tube with dark paper, in which you
have pierced a hole.
Start with a small hole (approx. 1 to 2 mm), which you can
then gradually enlarge. Cover yourself and the screen as
lightproof as possible with a dark cloth and allow your
eyes to adjust to the darkness. Unlike those obtained
with the lens, the images you see have a continuous
depth of field – which is the great advantage of pinhole
cameras. However, the picture is also much darker. The
bigger the hole, the brighter, but also the blurrier the
image becomes.