Last update: February 1, 2018Our Safe solar viewer is a
useful tool for tracking sunspots In the summer of
2018 we will be updating these pages with
modifications See the new section on smartphone photography with a super SSV LINK We
just added updates on pointing the SSV including a Another
reader has a suggestion on alternate lenses. LINK |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Get Ready for the August 21, 2017 Total Solar Eclipse.No Telescope? Not a Problem!Make Your Own Safe Solar Viewer,A Project for Kids of All Ages at a Cost of 1 to 20 Dollars.T. R. RichardsonCollege of Charleston Department of Physics and Astronomy This project was made possible thanks to the generous support of The American Astronomical Society, The National Science Foundation, The College of Charleston School of Sciences and Mathematics and The Department of Physics and Astronomy The viewers depicted on these page are part of the Eclipse Science Ambassador Project based at the College of Charleston Department of Physics and Astronomy. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 1. This is the latest prototype of our Safe Solar Viewer (SSV). It is not a telescope so you cannot look though it. Optically it is a crude ultra-long focal length telephoto lens with the film or CCD replaced by a white card. You observe the Sun by looking at the projected image. The viewer could easily be converted to a zoom telephoto by providing a method of adjusting the screen distance from the second lens. This viewer produces a 3-inch image of the Sun and is in effect a 7,600 mm telephoto lens. It is constructed with $6 of surplus optics, pieces of plywood, a tongue depressor, cardboard, rubber bands, screws and glue. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Introduction x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
This web location
details everything needed to make a Safe Solar Viewer
(SSV). Two types of projection viewers are described, a
simple one costing less than $1 and a more elaborate one
that can be made for twelve to eighteen dollars
depending on the items you have on hand. The viewers
depicted on these pages are part of the Eclipse Science
Ambassador Project, a public outreach effort based at
the College of Charleston Department of Physics and
Astronomy. Before we write about viewers, the next
section is a reminder about eclipse eye safety.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Eclipse Eye Safety x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
At the time of a
solar eclipse it is important to avoid eye damage by
using proper observing techniques during the partial
phases of the eclipse. Many people know it is unsafe to
look through a telescope at the partially eclipsed Sun.
Some do not realize that it is also dangerous to look
directly at the partially eclipsed Sun unless a safe
solar filter or some other technique is employed. The
late partial phases of the eclipse magnify this danger.
One of the safest ways to view the partial eclipse
phases is to project an image of the Sun onto a white
surface. Below we give the directions for constructing
two types of solar projection viewers.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The 5-Minute 55¢ SSV, a 1-Lens
Safe Solar Viewer x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
It
is surprisingly easy to make a simple solar viewer and
this one is similar to the really neat pinhole viewer I
was taught to make as a child but it is even cooler
because it provides a brighter, sharper image at an
affordable price. The SSV described in this section is
less complex than the one in Figure 1 above. Constructing
this viewer takes no more than five minutes after you have
gathered the materials. I have made dozens of these
viewers over the years as has my astrophysics colleague,
Dr. Laura Penny. All that is needed for the optics is a +1 diopter lens and this item is readily available locally. In fact you might already have one and not know it. A +1 close-up camera filter is just a +1 diopter lens and +1 reading glasses contain two such lenses. (Don't use the reading glasses of your parents or grandparents! Buy your own.) A pair of such glasses can be had at the discount stores for as little as $1 plus tax, providing the lenses for two viewers. We got ours at Dollar Tree. These lenses have a focal length of about 39.4 inches (1.0 meters) and produce a magnified image of the sun almost half an inch across, easily large enough to show the partial phases of a solar eclipse. There is some manufacturing variation in the focal length of these lenses so no matter which kind you use, the first thing is to measure the actual focal length of your particular lens. When the Sun is nearly overhead go outside with the lens, a white card, and a measuring tape. Hold the lens about 40 inches above the ground and project an image of the Sun on the card. Move the lens toward and away from the card trying to make the Sun's image as small as possible. Record the distance between the lens and the card when the Sun's image is the smallest. That is the focal length of your lens. Next find a box or tube long enough to hold the lens at one end and a piece of white paper at the other end exactly one focal length away from the lens. Stores like Kinko's have dumpsters that are good places to find such items that have been discarded. In the past we used a cardboard tube but a box (or cardboard you fold into a long skinny box) is easier to make and use. (See Figure 2a.) Attach the lens to an opening cut in one end and tape white paper inside the box at the other end. Once you have done that your SSV is finished and ready for use. With this SSV made with a +1 lens you can simply lean the viewer against a bench or other object at the correct angle so that the image of the Sun falls on the screen. We also make a shorter 1-lens SSV with a +2 lens that produces a bright quarter inch image of the Sun and the device is only about 20 inches long. If you stand with your back to the Sun and the SSV on your shoulder, you can practice using the shadow of the SSV on the ground to aim your viewer at the Sun. When the shadow of the tube or box is the smallest, the SSV is pointed at the Sun and an image of the Sun will appear on the viewing screen. It is quite practical to have this viewer on your shoulder with the Sun behind you. That way you show the solar disk to people facing you. See Figure 3 ( to be added soon). |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 2a. A simple
SSV using a +1 reading glass lens mounted in a cardboard
box cut down from a larger one. Leaving one side open
(or even retaining only one side as show below in a
different viewer makes the device easier to make and use
over one fashioned from a mailing tube.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 2b. The original box was 5 inches thick by 14 inches wide and 56 inches long. We kept the 5 inch width and ended up with a box 5 by 5 by 56. Then we cut off the end to make a focuser from the excess length and mounted the reading glass lens in the end of the focuser. As shown in Figure 2a, the focuser can be slid up and down the box and is held in place by binder clips. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The Image Size of a 1-Lens SSV x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
We have made these
SSVs from reading glasses from +1/2 to +2. The
fractional power reading glasses are more difficult to
find (though they do produce large images) and the
viewers are very long (often more than 6 feet) and so we
have ignored them in Table I below. This table shows the
lens power, the length of the viewer and the solar image
size.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The Super SSV, a 2-Lens Safe Solar
Viewer for less than $20 x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
With just a little
more work and expenditure of funds you can construct
your own Super SSV that will project an image of the Sun
two inches or more across. This SSV is just like the one
shown in Figure 1 above. This viewer needs two lenses of
the right kind, a support for those lenses, a white
screen, and a method of adjusting the distance between
the lenses Here we provide the details of our particular
viewer but a wide variation in parameters will still
result in a working design.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The Super SSV Lenses x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
This viewer needs an
objective lens with a focal length of anywhere from 600
mm to 400 mm. We used a 500 mm lens costing $1.50 plus
shipping. (At the end of this document we provide all
the lens details including suppliers, catalog numbers,
etc.) Lenses shorter than 400 mm also work but the
initial solar image produced is so small it tends to
burn the wooden support or the cardboard lens holder. If
you have a +2 close-up camera filter, you can use it
since its focal length is about 500 mm but you will get
better image quality if you cover the filter using
cardboard with a hole about an inch or a little more in
diameter.
The second lens is called a Barlow. It magnifies and projects the image of the Sun. Any good –18 mm to –30 mm focal length lens will work but that kind of lens is not something people usually have around the house. If you lens has a different concavity on the two sides, we orient the side with the deepest curve toward the Sun. In the Eclipse Science Ambassador workshops the children are using a –27 mm lens as the Barlow. We ordered ours online from Surplus Shed. (Details are at the end of this document.) |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Lens Spacing and Support x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The exact distances
here are not that important because many different
combinations will work; however, the distance of the
Barlow from the screen determines the image size. We now
build our SSVs with the Barlow held 12 inches from the
screen and the objective lens is on a holder (focuser)
allowing us to adjust its distance to bring the Sun into
focus. Its distance from the Barlow is about 19 inches
and the entire scope is less than 32 inches long. These
parameters give us a 2-inch image of the Sun which makes
this viewer a 5,000 mm telephoto lens and allows many
people to view the eclipse at the same time.
The current support parts are cut from half-inch plywood but there is nothing special about that choice. We have made the SSV using scavenged cardboard, Elmer's glue, and painters tape. See Figure 7. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 4. A view of the assembled SSV with the parts labeled. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The Super SSV Parts and Dimensions x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
In Figure 5 the
various parts of our SSV we are making with kids in
workshops are shown along with their dimensions. The
design uses a Barlow lens (-27 mm) at a fixed distance
(12 inches) from the screen showing the image of the
Sun. Increasing this distance projects a larger solar
image but makes the SSV longer. Using a Barlow lens of
shorter focal length also increases the image size
without increasing the length of the viewer. Decreasing
the projection distance produces a smaller, brighter
image. Our goal for this project was designing a viewer
that was less than three feet long while producing a
solar image one to three inches in diameter.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 5. The parts
of the Eclipse Science Ambassador Workshops SSV. All
wooden parts except for the guides (D) are cut from
half-inch cabinet grade plywood. The focuser guides are
made from a 6-inch tongue depressor cut in half.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Please note that
there is nothing special about the particular dimensions
we chose except for the approximate spacing of the
lenses. Changing the projection distance changes the
size of the image as does changing the focal length of
the Barlow (the projection lens.) Many different
materials can also be used. We have made SSVs
parts out of sheets of foam insulation and we made
several entirely out of cardboard. Figure 6 below
depicts a Super SSV using a piece of salvaged lumber and
cardboard from a dumpster. The only cost was for the
glue and the lenses. Figure 7 shows an SSV made from
cardboard and tape.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 6. An SSV made
with a scrap piece of lumber and cardboard. This
particular model is our favorite and works as well as
the ones made of plywood. It was our original design for
the Eclipse Science Ambassador workshops but it has to
be glued together in stages with clamping and drying in
between stages and thus requires too much time to be
completed in a workshop. In addition the effort would
exceed the interest and attention of the younger budding
scientists.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 7. An SSV made from the edge of a long cardboard box. This photo demonstrates how really easy these viewers are to make. My optics prof, Dr. Ron Edge (author of String and Sticky Tape physics experiments), would be please by this version. Ten minutes tops to construct this beauty which works as well as the fancy ones. The bottom 6.5 inches are a single piece that slides along the longer piece of the cardboard box holding the 500 mm lens. That movement is for focusing. Once the focus is sharp I fasten the focusing unit in place with binder clips. Is this solar image too small for you? Then make the projection distance larger. If you increase the 6.5 inches unit to about 18 inches you get a 3.5 inch solar disk. Not bad for $6.00 in surplus optics. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
More Comments on Solar Image Size x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Below in a table
showing a number of different layouts for the SSV and
the solar image size that results. A solar image of
1½ inches is the minimum we have chosen to for
our design and 3 inches is the maximum. Our
table covers that range with two different Barlow lenses
used in conjunction with an objective lens of 500mm
focal length. We like the lens with the –27
mm focal length for the Barlow, but if you want a larger
image than shown in Table II, just extend your
projection distance and the length of your SSV or order
a lens with a shorter focal length. Our supplier listed
at the end of these instructions has a numerous
suitable lenses in the focal length range from –18 mm to
–27 mm. In addition to the two Barlows in Table II, we
have made SSVs with Barlows having focal lengths
of –20 mm, –22 mm and –25 mm.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Using the SSV x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Unlike the one-lens
viewer the Super SSV needs to be supported for aiming
but a tripod is both unnecessary and undesirable. Even
an expensive high-end photography tripod will have a
small amount of play in the tripod head that will
frustrate the SSV operator. Try it if you wish but be
warned.
We have found that leaning the SSV against a chair, bench or even a cinder block makes a suitable alternative. See Figure 8. The block is especially useful because it can be situated two ways and cover a range of altitudes from about 15° to almost 90°. If the Sun is lower than 15° we simply elevate the rear of the SSV by placing a book or two under it. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 8a. An SSV in use leaning against a cinder block, our favorite support. The solar image moves as the Earth rotates so the operator must reposition the image over time. We think there is an important lesson in this activity for our younger operators. But if you tire of the constant readjustment on the Sun check out the equatorial mount designed by one of our readers as show later in this section. Another easy and functional way to use the viewer is to attach it to a long board and lean the board against a support. Figure 8b shows this approach.
Yet another way to control the pointing is to use a chair as show in Figure 8c. And then one of our readers, xxx, has made an equatorial mount for the SSV. See Figure 8d.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
![]() |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Figure 9.
Showing the method of aiming the Super SSV. The
bright spot next to the Barlow lens is the image of
the Sun. It is an easy adjustment to move the viewer
so that the image falls on the lens. That is all
there is to aiming this viewer. The cardboard taped
to the Barlow support is simply there to cast a
larger shadow and improve the contrast in the image.
A larger board could do the trick but cardboard is
free.
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Smartphone or Other Camera Photography
with the Super SSV x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
This
helpful suggestion was sent in by one of the readers of
these pages and I know it works because I have done a
similar thing with previous very long one-lens SSVs.
Figure 10 shows an image of the partial solar eclipse in
October 2014 with this method. I have been too busy with
kids workshops making SSVs to work out the details for the
current viewers so you will have to experiment a little.
Send some pictures if you try it. Here is the method. Extend the length of the rail by the minimum focusing distance of your camera or smartphone. Where the screen is located replace the upright board with two vertical strips attached to the rail. The reader suggested using the same sort of sticks used as guides for the focuser. Between these uprights attach something translucent such as tracing paper (suggested by the reader) or wax paper (something that has worked well for us in the past). At the back of the rail you will have to devise a means of holding your smartphone or camera. We have used a piece of plywood (just like the screen upright that is no longer used) with a holed drilled for the camera lens at the same position as the SSV lenses to keep things aligned. We glued strips of wood to the back of the plywood to position the smartphone camera lens in the center of the hole and had Velcro or rubber bands to hold the phone. It may be necessary to enclose the SSV from the Barlow upright to the translucent screen to keep stray light away from of the transparent material to have the best contrast for photography. That is the way our previous version was configured. Scrap cardboard or a mailing tube cut to the right length could do the job. But the solar image might be bright enough that this added step is unnecessary. Again you will have to do some tests. Happy viewing! |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Lenses and Suppliers x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
The
lenses in our Super SSV were
purchased from Surplus Shed, 1050 Maidencreek Rd.,
Fleetwood, PA 19522, (1-877-778-7758),
www.surplusshed.com. The lenses in the table below are
the ones we are using in our workshops. To make it
easier to order the proper lenses Surplus Shed now has a
direct link on their home page to a package with the
lenses you need to make the two-lens SSV. Either of the
first two lenses are fine for the objective. Surplus
Shed is currently out of the second lens and there is no
advantage to its larger size. They are likely to have a
supply of that lens before eclipse time but if they do
not the other one is fine as is a +2 reading glass lens
from Dollar Tree or similar supplier. To improve image
quality and keep the solar image from being too bright
we restrict the lens opening to about 30 mm for either
lens.
Surplus Shed did have plenty of the listed Barlow lenses in stock but if for any reason they run out, their lens finder link will help you find a lens in the focal length range around –25 mm. Just make sure you select a lens with a diameter of 15 mm or more.
As the eclipse gets closer other options on lenses might be worth considering. I am posting a solution here from one of our readers, Tom Feller. Below is what he discovered. "Unfortunately, I came across it last week and have been unable to obtain a Barlow lens of the requisite focal length to construct an SSV in time for the eclipse. However, a family member had old eyeglasses in the range of -10 diopters which are progressive bifocals and therefore of varying strength throughout the lens. I combined one of these -10 lenses with a +1.25 diopter (800 mm focal length) reader lens to make a super SSV. The solar image is 2 to 3 times that of a single +1.25 lens SSV; it shows a solar disc and clouds moving underneath with equal clarity compared to the single lens viewer. I suspect that the progressive prescription along with an astigmatism correction has some impact on image size, quality, and position but this super SSV works and is available in time for the eclipse. Use of old eyeglass lenses may be a way for some of the people you are working with to enjoy a better view of the eclipse if they have access to surplus lenses that correct for severe myopia." I think you can see that he has a great idea with this approach. The Barlows we use are -3.7 diopters (-21 mm fl) and -5.6 diopters (-18 mm fl) so a -10 diopter Barlow would produce a large magnification of the image of the primary lens. |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Parting Words x |
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Best of luck with your
SSV construction efforts and your weather on eclipse day.
I would suggest that you go outside with your SSV a week
or more before August 21 at the same time the eclipse will
occur and practice, practice, practice. It may be a long
time before you have an opportunity like this again. If you have any ideas you want to add to this effort or any questions, please email me (richardsont AT cofc dot edu). I hope you have good weather on eclipse day. T. R. Richardson |