Safe Solar Viewer

Last update: February 1, 2018

Our Safe solar viewer is a useful tool for tracking sunspots
We are currently at a solar sunspot minimum. But get
ready because a new maximum will be starting soon.

In the summer of 2018 we will be updating these pages with modifications
to our SSV permitting smartphone photography of sunspots and information
on how to calculate the solar rotation rate from your photos-a cool project
for middle school students.

See the new section on smartphone photography with a super SSV LINK

We just added updates on pointing the SSV including a
neat equatorial mount designed by one of our readers. LINK

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. Richardson 
College 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
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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
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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
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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.

Figure 2c. Here we see one half of the reading glasses still in the frames and taped to the front of the focuser. It is usually easy to pop the lens out of the frame if you wish to mount it in some other way. As shown we left the +1 diopter indicator in place. The rhinestones in the lens frame are not functional.

Figure 3a. Here we see a solar viewer held on the observer's shoulder so it can be seen by those people standing around the person holding it. It is a simple matter to stand with the Sun at your back and match the shadow of the box to the viewing screen. With a little practice it is easy to bring the Sun into view. With the single lens SSV it is relatively easy to keep the Sun always in view.

The only problem we have found with this method is a person's hair can block the view.

Figure 3b Here we show the objective of the one-lens SSV made with a +1.5 diopter reading glass lens. The hole is deliberately smaller than the lens for two reasons. Using the full lens produces an excessively bright image that is difficult to view and a small hole (about 3/8 of an inch) produces a much sharper image.

The Image Size of a 1-Lens SSV
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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.

Table I 1-Lens SSV Sizes (approximate values)

Power	Focal Length	Solar Image

+1.00	39 inches	0.40 inches
xxx
+1.25	32 inches	0.31 inches
xxx
+1.50	26 inches	0.26 inches
xxx
+1.75	23 inches	0.22 inches
xxx
+2.00	20 inches	0.20 inches

The Super SSV, a 2-Lens Safe Solar Viewer for less than $20
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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
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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
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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
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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.

    A. support rail, 3.5 by 32 inches
   B. focuser upright, 3.5 by 3.875 inches
   C. focuser foot, 3.5 by 1.75 inches
   D. focuser guides

E. cardboard lens holder, 3 by 3 inches
F. cardboard lens holder, 3 by 3 inches
G. Barlow upright, , 3.5 by 3.875 inches
H. screen holder, 3.5 by 4.375 inches

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
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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.

Table II SSV Lens Layouts (approximate values)

Barlow focal length	Projection Distance	Solar Image	SSV Total Length

–27 mm	8 inches	1½ inches	28 inches
xxx
–27 mm	10 inches	1¾ inches	30 inches
xxx
–27 mm	12 inches	2¼ inches	32 inches
xxx
–27 mm	14 inches	2½ inches	34 inches
xxx
–18 mm	8 inches	2 inches	26 inches
xxx
–18 mm	10 inches	2½ inches	28 inches
xxx
–18 mm	12 inches	3 inches	30 inches

Using the SSV
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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.

Figure 8b. This image shows a Super SSV simply taped to a long board and leaned against a car as a means of support. Anything that allows the board to rest at the appropriate angle can provide the support.

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 8c. This image shows a Super SSV sitting in a lawn chair to provide support and assist in aiming. This simple method works quite well.

Figure 8d. This image shows a Super SSV on an equatorial mount devised by John Dixon, one of our readers. He uses a galvanized pipe flange as the polar bearing and a piece of pipe as the polar axisI think it is an ingenious solution to the problem of tracking the Sun and I and can't wait to make one myself but only after the eclipse.

See this link for a closeup of the important details.

Pointing the SSV at the Sun is simplified by the open design without a tube. This allows the operator to see the image of the Sun that forms on the Barlow holder. Moving that image until it falls on the Barlow lens allows the light to pass through the lens and produce a magnified image on the screen. See Figure 9.

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
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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!

Figure 10. A photograph made with a one-lens SSV. Here we show the image of the setting Sun while the solar eclipse of Oct. 23, 2014 is in progress. The image of the Sun is projected onto a sheet of wax paper from the kitchen and photographed with a DSLR camera equipped with a closeup attachment. Not only is the solar disk visible but also the outline of the horizon with buildings and a tree on the left.

Lenses and Suppliers
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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.

Purpose	Description	Specifications	Item #	Price
objective	Educational DCX	38 mm x 500 mm fl	L1907D	$1.25
objective	Educational DCX	50 mm x 500 mm fl	L1917D	$1.50
Barlow	Kodak DCV	21 mm x -27 mm fl	L3964	$4.50

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
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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