Yet another incarnation of the Solar Eclipse Viewer! One limitation of that viewer had always been the size of the final image of the Sun - too tiny, with a limited angle of view so pretty much only one person could use it at any one time. This Instructable attempts to fix that by using a curved mirror to project and magnify the image.
Step 1: How It Works
The working principles are pretty much the same as before, hence if you're looking for a more in-depth explanation on image projection, intensity and lenses, refer to the first part of the Solar Eclipse Viewer.
As before, a lens is used to create a projected image. However, instead of projecting the image directly onto a screen, the image is now reflected off a convex mirror and then onto a screen. This can be done by placing a convex mirror around (not at) the focal point of the lens. At a particular mirror-screen distance, the image will then come into focus.
The final image will appear magnified, but at a lower intensity (after all, you've captured the same amount of light from the Sun, but you're spreading it over a larger, magnified image).
Step 2: What You'll Need
There's a lot of flexibility in this build, so this is a general list of components needed. Adapt to your local supply sources accordingly.
- A +1.50 dioptre pair of reading glasses. Generally any power between +1.00 and +3.00 can also be used, but the image size and intensity will vary slightly, and you'll need to work out experimentally what the best focus distances are.
- A convex blind spot mirror. Usually sold in pairs at auto stores.
- A long PVC tube, approx 20 - 30 mm (~1") inner diameter, length approx 45 cm (17"). This tube is the main optical tube for the lens.
- A PVC end cap for the above tube.
- Two short lengths of PVC tubing, approx 20 cm (8") length. Their absolute diameters are not critical, but one tube must fit snugly in the other, and slide with a bit of friction. These two tubes will form the focus mechanism for the mirror.
- A PVC elbow joint that fits the smaller of the two PVC tubes above.
- Various pipe clamps. Or anything else that allows you to clamp two PVC pipes together, in a parallel fashion.
- Various nuts and bolts to connect things together.
- Epoxy for plastic.
- L brackets (not shown in the picture here, see Step 6.)
- A projection screen (not shown in the picture, see Step 6.)
A note on substitutes: Duct tape can usually be substituted for clamps and other fasteners. Hot glue can be used during prototyping, but is not recommended for a final build. Solar viewers can get very hot when they are out in the Sun for long, and this can sometimes cause hot glue joints to melt and loosen.
All you need are some basic tools (hammers, screwdrivers, files, saws, drills). Using a rotary pipe cutter is recommended for cutting the PVC pipes.
Apart from the usual safety considerations when working with tools, some extra precautions need to be taken when working on optical components for solar viewers:
- Never look at the Sun directly through a lens, or even with the naked eye.
- Be aware of where your lenses and mirrors are projecting, as a well focused image of the Sun can set things on fire.
Step 3: Prepare the Lens Assembly
Remove one lens from the reading glasses.
Drill a large hole in the PVC end cap, enough to fit as much of the lens as possible. The larger the available lens area (aperture), the brighter the image will be.
Cut and file down the lens so that it fits snugly into the end cap, and then epoxy it in place. Ensure that the lens is seated perpendicular to the axis of the lens cap. It's a good idea to apply masking tape onto the lens during cutting so that you don't accidentally scratch the lens.
Pop the end cap onto the long PVC pipe, and check that it gives a good, undistorted projected image of the Sun.
Quick hack: If cutting and filing the lens sounds like too much trouble, just duct tape or epoxy the lens onto the end of the long PVC pipe. Any method works as long as the lens is firmly attached, and gives a good image at the other end of the tube.
Step 4: Making the Mirror Assembly
Pry off the back of the blind spot mirror. The back usually has two parts, to allow for the rotation of the mirror in its holder. Drill a hole in the outermost back piece, so that you can fit a long bolt through.
Drill holes through the PVC elbow connector, then bolt the mirror to it.
Step 5: Adding the Focus Mechanism
Clamp the larger of the two short PVC pipes onto the long PVC pipe, leaving a spacing between the pipes.
Attach the PVC elbow with the mirror to the other short pipe, and slide it into the clamped pipe.
Now bring the entire viewer out to the Sun and try getting an image. Clamping the viewer to a tripod helps immensely here!
Check that the image from the lens falls around the centre of the mirror. If not, increase the spacing between the two pipes until it does.
Slide the mirror assembly along the sleeve until a focused projected image is obtained on a piece of white card.
Step 6: Adding a Projection Screen
Attach L brackets to the clamps, and attach a projection screen to it.
The screen used here was from the backing of an old desk calendar. Pretty much any flat, opaque board would do. The projection screen itself can be a smooth, white sheet of paper or card that is glued onto the board.
As for the size, a larger size would screen off more light from the Sun and make viewing somewhat easier, but a larger screen can also make the viewer unwieldy. It's better to keep the size manageable (approx 20 - 30 cm, or 1', on the sides), and sit in a darkened area like a tent instead.
Step 7: Using the Solar Eclipse Viewer
Finally, add a mounting bracket to the viewer, so that it can be attached to a tripod. Here's one rigged up from a T bracket. There's also always duct tape.
Aiming the viewer is easily done by finding the position where the lens tube casts the shortest shadow. At that point, the lens tube is aimed directly at the Sun and you should see the image of the Sun on the screen. Adjust the mirror focus and position until a good image is obtained.
The Solar Eclipse Viewer is also capable of imaging larger sunspots, but unfortunately as we're hitting a Solar minimum (around 2017 - 2019), opportunities for sunspot observation would be much harder to come by, for the next 4 - 5 years at least.
So for now, simply enjoy the view if you build one and are lucky enough to be in a solar eclipse zone!
zachschi made it!