By now, if you live in the USA, you know there's an eclipse coming August 21, 2017. Even if you're not all that excited about it, you know you're gonna watch it... and you'll probably try to photograph it.
Hopefully, you already know not to stare at the Sun without protecting your eyes -- and I don't mean with ordinary sunglasses. You might not have realized that your camera needs a similar level of protection. That's most of what this instructable is about.
However, you also should know that a solar eclipse is difficult to photograph. It isn't just that the sun is too bright; it's also small. The Sun and Earth's moon appear to be about the same size as seen from the Earth, which isn't something that has always been true nor will it always be true, but I digress... the point is they're both small. They only take up about 0.5 degrees. A full-frame 135-format (35mm film) camera, or the digital equivalent, captures images that are approximately 36x24mm. Given a lens of focal length F, the diameter of the image produced for the sun or moon is roughly 0.0087 * F. The longest focal length lenses most people own are about 300mm, which by our formula gives an image a mere 2.61mm across. Let's say you're using a Sony A7RII with it's impressive 42MP full-frame sensor: the image of the sun/moon would only cover about 260,000 pixels -- fewer pixels than a typical $5 webcam! You also can forget about using your cell phone's wide-angle lens for this....
The Canon PowerShot SX530 HS is a cheap 16MP super-zoom camera that goes to a full-frame equivalent of 1200mm focal length. Well, that ends up making the sun/moon cover nearly half the sensor height, giving about 2.4MP of useful data -- nearly 10X what that 300mm lens on a high-end Sony A7RII would deliver, but at very low cost and a lot easier to carry. I know 2.4MP doesn't sound that great, but remember that HD TV is only about 2MP. The problem we're dealing with in this instructable is that the SX530 HS doesn't accept filters, and it needs a solar filter... so, we'll make our own using a 3D-printed holder.
Have a different camera that's appropriate, but needs a filter? No problem; we also present a 3D-printed screw-in holder you can use with any camera that has a standard filter thread.
Step 1: Stuff You Will Need
What do you need? Well, nothing too expensive... but you need to get stuff fast now if you want to have it usable for August 21's eclipse. Here's what we used:
- Optionally, a Canon PowerShot SX530 HS camera. We got ours as factory refurbs for $130 each, but right now they sell it for $180; of course, it's free if you already have one. Lots of superzoom cameras would probably do just as well with minor mods to the 3D-printed parts described in this instructable. This instructable also tells you how to make a filter to use with any camera lens that has a standard screw-in filter thread -- as shown in the photo.
- AstroSolar Safety Film. This stuff isn't cheap, but don't compromise on this -- this is a lot more effective, and safer, than regular ND filters, exposed color film, or any of the other hacked viewing filter materials. This very thin metalized plastic material makes a really high-quality solar filter, and it is shockingly strong, but it is a pain to handle. You'll also notice it usually has some waves in the material as mounted, but they're harmless optically. Even the smallest sheets are probably big enough to make more than one filter... and making more than one is a good idea, just in case something bad happens. Our roll cost about $100, but is enough for nearly 100 filters this size; $25 should buy a sheet big enough for at least several filters.
- A 3D printer. We used our MakerGear M2 with black PLA filament. The filament cost is pennies per filter made.
- Spray contact cement (and an appropriate place to use it). I hate this stuff, but it works great. The particular one we used was 3M General Purpose 45 Spray Adhesive, but I suspect any would work the same. We were unable to get a direct response from the manufacturer as to whether the cement might cause damage to the film over a long period, but so far so good (and if we hear otherwise, we'll revise this document); if you're worried, thin two-sided tape is what the manufacturer recommends for fixing the film to cardboard, and it would work with the 3D-printed holder too.
- A soldering iron. Used for welding PLA.
- Scissors. For trimming the safety film without putting it under stress that could stretch it.
One more note: bring a second camera! Why? Some of the most interesting things about an eclipse are not the eclipse itself, but the weird lighting, shadows, and people watching the eclipse. In fact, that's a great thing to use your DSLR or cell phone for while the SX530 is capturing the event in the sky.
Step 2: Print the Filter Holder
The Canon PowerShot SX530 HS doesn't take regular filters, but the lens does have a simple bayonet mount (for a hood?). Thus, we designed a 3D-printable holder that simply bayonets to the front of the lens. The design is freely available as STL files as Thingiverse Thing 2475342, Solar Filter For Canon PowerShot SX530 HS.
If you are using a different camera that accepts standard threaded filters, instead use our also freely-available Thingiverse Thing 2485988, 3D-Printed Screw-In Lens Filter Holder. It assembles and works identically, but instead of having a fixed-size bayonet mount, you use the Thingiverse customizer to specify the filter thread size and it will create the STL file for you. Actually, this thing is a completely parametric OpenSCAD program we originally wrote to generate custom lenscaps, and using the customizer it can still make those too.
The holder is made in two pieces: an inner bayonet part and outer cover. Both can be printed using PLA without supports. The bayonet version has an overhang for the bayonet, but it's small enough that sagging isn't an issue; the screw-in design actually prints the fine threading (no tapping required), but is fully self-supporting. Use a filament that is as opaque as possible. Once the parts are printed, clean-up any extrusion threads and test-fit the bayonet onto the front of the lens -- you can't tweak any of this once the next step has been done.
Step 3: Spray the Surface of the Inner 3D-Printed Part
Only the inner part of the mount, which has the bayonet on it, needs to be sprayed with cement -- and not much of it. To contain the cement overspray, we made a little spray booth out of a cardboard box. Multiple inner parts were then placed on a sheet of clean scrap paper with the side that was printed facing down now facing up -- that's the side that gets glued. Spray the parts lightly from straight above. You don't need much stick for this; it's primarily to hold things during assembly of the filter, and is only needed to prevent slipping after assembly.
Step 4: Bond and Trim the AstroSolar Film
Lay out the AstroSolar film on a clean table. It doesn't take much material for one filter, but we made enough filters for an entire array of SX530 cameras that we're using, so we bought a roll with a protective backing; yours will probably be a smaller sheet with a backing sheet behind it. Either way, lay it flat against the table with the backing sheet down. The rolled material tends to curl, but you can tape or weight-down the edges to keep it flat.
Take the slightly dried, but still tacky, inner part and press it onto the film by touching one edge and then gently pivoting the part flat against the film. Just keep in mind that you can't really clean the film, so be careful not to get it dirty -- and don't stretch, kink, or puncture it.
Once pressed down on the film, use scissors to trim the excess film around the inner part. The trimming isn't critical; just get as close as you can.
Step 5: Assembly and Welding
The outer part fits over the inner part, covering where the film was glued. It shouldn't take any force to put it on, because it is printed toleranced to allow some play.
We were surprised to discover that even a tiny bit of excess cement was enough to hold the complete assembly together. However, we used a cheap soldering iron to gently weld the seam between the inner and outer plastic parts. Out of respect for Paul Eberhart, my student who did this welding, I'll also add that you don't really want to use your best soldering iron tip for this because it will get a trace of PLA plastic on the tip. In any case, the welding is quick and easy, and the resulting part is strong. How strong? Well, once we slipped with the soldering iron and burnt a whole through the film -- so we decided to destructively test that filter. Wow, that stuff is strong! Moderate amounts of force could stretch the film, but actually breaking it took much more force than any of us would have guessed. The cement bond and weld never came apart.
Do not worry if the film looks a bit wavy. That's normal and harmless even for the commercially-mounted versions of this film material. However, be careful not to crease, stretch, or puncture the film. If you get a fingerprint on it, just leave it there -- attempting to clean it is likely to wreck the film coating, but the fingerprint is highly unlikely to leave any trace in your images.
Step 6: Use It
Done. Now use it. Yes, NOW. Don't wait for the eclipse to test it out!
The filter gets mounted on the lens front bayonet by aligning the bayonet tabs, pushing the filter on, and twisting a little to lock the bayonet. There is no need to fully engage the bayonet; just a slight twist will lock the filter firmly in place. The key is not to handle this too roughly because you don't want to stress the film, although it's again worth mentioning that gentle waves in the filter material are harmless whereas pulling it tight might damage the coating.
As dark as this filter is, the sun is still quite bright through it. The camera's meter will also be fooled into overexposing because the Sun will only cover a portion of the frame, with the rest essentially black. Thus, we recommend setting the exposure around 1/1000s at ISO 100 (although you should be aware that might not be enough exposure during the couple of minutes of totality of a complete eclipse). The fast shutter speed will also help keep the image sharp, but you'll definitely want a tripod -- it's very difficult to hold a 1200mm lens still enough for framing.
To frame the Sun, start with the lens set to a relatively short focal length. Don't look at the sun, but only at the rear LCD of the camera. Center the bright dot that is the Sun, then zoom the camera to 1200mm. The Sun should look a lot like the photo shown here, which reveals not only the Sun's dark spot in some detail, but also some of the texture of the Sun's surface in general and even a bit of the unevenness at the Sun's edge. Enjoy!