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How to Make a 2-Lens SSV

Figure 1. A smartphone photo of the solar image of a 2-lens SSV

This SSV had a 52 mm x 600 mm objective and a −27 mm focal length Barlow. The lenses cost $12.50 plus shipping. The image was taken on July 9, 2023. The original photo was black and white and the NASA SDO/HMI continuum color was added in processing.

The numbers are the sunspot group labels assigned to sunspot outbursts in order as they develop. The arrows point to newly developed regions that had not been assigned numbers at the time the image was made. Although groups 3364 and 3360 seem to be missing, they were apparent in the original file before it was downsized for the web. (Photograph by the editor.)

After the 2017 total solar eclipse, those of us in the Eclipse Science Ambassador Program made an inventory of everything learned from the workshops in which kids made 2-lens SSVs. Based on those lessons, we made improvements to the SSV and simplified the construction. The 2017 SSVs were 36 inches in length and had the objective on a sled to adjust the sharpness of the solar image. We find it better to have the projection screen and objective on fixed supports with the Barlow on a movable support in between them. We also increased the screen separation to 40 inches, thus resulting in a 4-inch solar image with the current optics available.

Figure 2. A pair of 2-lens SSVs side by side using the 2017 optics

The upper viewer has a 50 mm x 500 mm objective while the lower one has the 38 mm x 500 mm objective. The image in the upper viewer is brighter because of the greater light gathering power of the the 50 mm lens. Both of these SSVs are made using a 40-inch Uline shipping box. The aluminum foil on the Barlow holder keeps the cardboard from being charred by the solar image if the light drifts off the Barlow lens.  (Photograph by Bart Thomas)

This list shows what you will need to construct a 2-lens SSV identical to the ones we are now making.

In the 2017 eclipse workshops, the kids assembled wooden SSVs from precut parts. That approach involved considerable shop time before the workshops. Over 3600 holes of six different sizes had to be drilled in the various parts for all the SSVs constructed in the workshops as well as those given to teachers! That drilling came after 780 wooden parts were cut from sheets of half-inch plywood. There had to be an easier way.

We now build 2-lens SSVs using a standard cardboard shipping box, an idea SSV community member Bart Thomas of the Collier County Public Schools developed. He discovered the 6 x 6 x 40-inch Uline shipping box was perfect for for our SSVs. (Uline Catalog # S-18430) Bart has conducted teacher workshops for his county's science teachers making SSVs with these boxes and that work has been quite successful. (Go to Bart's workshop instructions. Please note these instructions are form an early workshop using a 36-inch long box but we now recommend a 40-inch box.

Other companies sell similar products. We use the Uline boxes because they are made from sturdy cardboard and come in the sizes we find useful. The cost for the 40-inch box is $2.61 plus shipping with a minimum order of 25 boxes; however, if you are not conducting a workshop for a group, contact Uline customer service to order a few sample boxes. Alternately, if you can find a local business that uses these boxes see if you can obtain a few from them. If neither of those options work for you, then you could cut up boxes and glue together a result that would match the Uline box in size. That homemade box would make a fine SSV. Using a Uline box avoids a great deal of time spent measuring, cutting and gluing. Here is a link to a web page for making your own SSV boxes using various size cardboard boxes and scrap cardboard. Those with a shop could still make the SSV from wood scraps as many did for the 2017 eclipse.

Our Barlow holder is also constructed from a Uline box. They offer a 6 x 6 x 12-inch box (Uline Catalog # S-4128) for $0.61. We cut these boxes in half and make two Barlow holders from each one.

Figure 3. The Uline shipping box for our 2-lens SSV

Bart Thomas has tested SSVs of various lengths using objective diameters of about 50 mm. His tests found that the lenses we suggest produce a solar image about 4-5 inches across (depending on the Barlow focal length) in a 40-inch long box. That image size works well in a box that is 6 x 6-inches on its end. He also found that the solar image became too faint for easy viewing in longer boxes that produced larger images and that is the reason we have settled on the design show on these pages.

If you desire a larger solar image, you will need to make a longer SSV and also obtain an objective that has a larger diameter. For larger images, we have designed the large image safe solar viewer, LISSV based on another Surplus Shed lens set with a larger objective.

There are now three choices at Surplus Shed for the 2-Lens SSV.

In a 40-inch SSV, all of these lens packages will produce about a 4-inch solar image with the 600 mm version producing a slightly larger image. Which one should you choose? The two achromats will show all but the smallest sunspots. In a recent side by side test, one SSV with the 52 mm x 600 mm objective in a Uline box performed as well as the solar projection device sold to schools for $500. The 600 mm focal length objective is our lens of choice.

If you are making an SSV with your own lenses, we have tested lenses from 325 mm to 600 mm focal length and they work as objectives in a 40-inch SSV. Even longer focal length lenses will do just fine but will require a longer box. We have made several SSVs, with objectives scavenged from cheap, discarded "hobby-killer" refractors. If you want to use an objective lens with a focal length greater than about 600 mm, plan on making an SSV longer than in our instructions in order to have an image size similar to ours.

As noted above, we are making 40-inch long SSVs using a Uline cardboard shipping box. The boxes are shipped flat and we glue them together to make the SSV. What glue should you use? The answer is any glue that works for you on paper products. We like the original Titebond wood glue because it has good "grab" when parts are put in contact. We have also used Titebond II when we were out of the original Titebond. Both are a PVA glue similar to school glue, the white glue that might already be in many homes with school-aged children. A good quality white glue works well. Remember, we are gluing cardboard, so a thin application is all that is necessary. For these water-based glues, you should use weights or clamp the pieces for at least 20-30 minutes before moving to the next step.

Below are the steps we follow in making the 2-Lens SSV. Please note that when the text refers to the "front" of the SSV, it means the face of the box holding the lens and the "back" is the side holding the screen. Likewise the "top" is the open side of the box and the "bottom" is opposite the top. A Picture will be posted when it is ready to be uploaded.

1. 

The long flaps on what will be the open side of the SSV are folded over and glued to the outside of the box and clamped in place. See Figure 4 below. We let the glue dry completely, usually for several hours. You could simply cut them off but gluing them in this fashion adds strength and helps the SSV hold its shape.

Figure 4. A finished 2-lens SSV showing the details of construction

Notice the top flaps turned out and glued to the outside. We find doing so makes the device more robust. We also glue a length of hardboard (some plywood world also work) to the bottom to add stability and help the box keep its shape. The Barlow holder is the part of the viewer held by binder clips with the aluminum foil on the front. Sliding the holder back and forth allows the solar image to be brought into sharp focus.

2. 

Next we decide which end of the box will hold the screen and glue the short flap at that end to the long bottom flaps. We use a carpenter's square or similar tool to make the side that will hold the screen square to the sides and bottom of the box. If you lack a carpenter's square, then use the cover of a hardback book. Also, a friend or neighbor with a table or contractor's saw could easily make one from a small piece of lumber or plywood. We use weights to hold the short flap down until the glue has dried.

3. 

Then we glue the flap on the other end of the box and let weights hold that flap down until it has dried.

4. 

Now we glue a 6 x 40 inch piece of hardboard to the bottom of the box. If you don't have access to a saw, you could buy a 6-inch wide board from a hardware or big-box store. A 36-inch length would work yet it would be better to buy a 48-inch length and cut it down.

5. 

Next we make the Barlow holder either from half of a 6 x 6 x 12-inch Uline box or gluing together a box of the same size as shown in Figure 5 below. The idea here is to have a Barlow holder that just fits in the SSV while holding the Barlow the same distance from the bottom and sides of the SSV as the objective. That way moving the holder forward and back to adjust the sharpness of the image will keep the Barlow lens aligned with the objective lens.

Figure 5. A finished Barlow holder minus the aluminum foil

The foil keeps the concentrated light from the objective from charring the cardboard. This holder is constructed by gluing two box halves together such that the holder just fits into the SSV with no wiggle room.

6. 

Then we mark the front of the SSV at its center and use a t-pin or similar item to push a hole through the center of the front end. We also hold piece of cardboard the exact width of the inside of the SSV against the SSV front and push the t-pin through it as well.. This piece of cardboard is a template for marking the position of the Barlow lens on the holder.

7. 

Next we hold the cardboard template against the front of the Barlow holder with a piece of congregated cardboard under the template but not the holder. This cardboard compensates for the flap glued inside the front of the SSV. Then we put a t-pin in the hole in the template and push it through the front of the Barlow holder to indicate the center position of the Barlow lens.

8. 

After marking the position of the lenses, we drill or cut holes for those lenses. Drilling corrugated cardboard without tearing it is a difficult task. For just one or two SSVs, marking the appropriate sized circle and cutting the opening with an Exacto knife or similar tool with a sharp blade is the best approach.

For making many SSVs, drilling is less time consuming. We have had some success with freshly sharpened Forstner bits, such as those from Freud. It helps to use a drill press and to have a thin board with a hole the size of the bit against the cardboard. The other key to success is to drill from both sides of the cardboard. Once the bit cuts through the top layer of the cardboard, we move the bit to the other side and resume drilling. The drill press cannot drill from the backside of the SSV front so the guide board is essential here.

Forstner bits are expensive and we discovered a better choice for drill bits. Cheap diamond hole saws available from Amazon make a hole in corrugated cardboard without tearing because they are really wearing a hole in the cardboard. Two things are helpful for the best results. Again a wooden drill bit guide is useful and having cardboard rather than something hard like wood on the backside gives us excellent results.

9. 

For both the front of the SSV and the Barlow holder we drill a hole about 4-6 mm (about ¼-inch) smaller than the lens as a stop to prevent the lens from falling out the back. Then we drill a hole the same diameter as the lens in a stack of corrugated cardboard the same thickness as the lens and an inch or two larger than the lens diameter. See Figure 6.

Figure 6 The objective lens holder made from a stack of cardboard

10. 

Now we prepare the two-part achromatic lens for mounting. First we put three small pieces of painter's tape on the edge of the thicker lens spaced 120° apart on its concave face (the side that is thinner in the middle). These pieces of tape act as spacers. Then we put the lenses together and run scotch magic tape around the outside to keep them together. How do the go together? The thinner lens has a flat face and a convex face (bulging outward in the center). The flat face is on the outside and faces the Sun. The convex face fits against the thicker lens and they are kept apart by the thickness of the painter's tape. See Figure 7.

Figure 7 A closeup of the front and side of the objective lens

In the side view of the objective, the face of the lens pointing to the right will be on the outside of the SSV and point toward the sun.

11. 

Next we fit the objective in the cardboard mount made from a stack of cardboard sheets glued together. We like the objective hole to be so close in diameter to the objective that friction holds the lens in place. If we can't match the sizes that well, the we put the lens in the mount and glue quarter inch wide pieces of cardboard or wood wedges to the lens mount to hold the objective in place. After that glue dries we glue the cardboard mount to the front of the SSV centering it on the hole we put there.

12. 

After that we install the Barlow in its cardboard mount the same way we did the objective and then glue the cardboard mount to the front of the Barlow holder. To prevent the concentrated solar rays of the objective from burning the cardboard, we install aluminum foil around the lens on the Barlow holder using double stick tape.

13. 

install the screen in

14. 

position the Barlow holder and test.

15. 

Adjustments

Making a Barlow holder begins with half of a box at least as tall as the Uline box.

Next cut the height of the box to the inside height of the Uline box or a little less.

Next cut the width of the Barlow holder to about ¼-inch less than the width of the inside of the Uline box. Normally the hole for the Barlow lens is drilled after the two pieces are joined, but the Barlow holder was for a travel SSV and the front hole needed to be drilled before they were joined.

When the box is ready, both halves are put into place in the SSV, clamped to the sides of the box and glued so that the holder is a perfect fit to the box.

The last step is to add some aluminum foil to keep the image of the Sun formed by the objective from burning the cardboard of the Barlow holder.

(Note: neither the editor of these pages nor his colleagues or the College of Charleston have received any compensation from Surplus Shed. We use their optics because they are the best source we have found. Also neither of the parties have received any compensation from Uline for promoting their products.)