The Aug. 21 solar eclipse may become the most photographed in history, with tens of millions across North America attempting to capture the long-awaited event with everything from high-performance film and digital single-lens reflex cameras -- DSLRs -- to inexpensive point-and-shoots.

And in the age of smartphones, when taking quick snapshots is as simple as reaching in purse or pocket, the urge to capture an event as heavily publicized as the August eclipse will be irresistible to many.

But professionals have a few words of strongly urged advice: never, ever point any type of camera, telescope or binoculars at the sun, even during a nearly full eclipse, without a certified solar filter firmly attached to the front of the lens.

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The only exception is during the brief period in a swath of the country when the moon completely blocks out the sun's dazzling brilliance. For the Aug. 21 eclipse, that fleeting opportunity will last just two- to two-and-a-half minutes along the 70-mile-wide path of totality that stretches from the coast of Oregon to the coast of South Carolina.

All of North America will see at least a partial solar eclipse on Aug. 21, 2017, and a 70-mile-wide swath of the country from coast to coast will get a total eclipse. Michael Zeiler, www.GreatAmericanEclipse.com

And even in the path of totality, filters are a must during the partial phases before and after totality when the moon covers some, but not all, of the sun's visible surface.

"IT IS NEVER SAFE TO LOOK AT THE SUN WITHOUT PROPER EYE PROTECTION WHEN ANY PART OF IT IS VISIBLE BEHIND THE MOON!" camera-maker Canon states on its eclipse photography website, using red, boldface, capital letters.

"THIS ALSO INCLUDES NOT LOOKING THROUGH YOUR CAMERA'S VIEWFINDER WHEN PHOTOGRAPHING THE ECLIPSE - USE A SOLAR FILTER ON THE FRONT OF THE LENS, AND LOOK THROUGH YOUR LCD SCREEN INSTEAD OF THE VIEWFINDER!"

As amateur astronomers and even school kids know, unfiltered sunlight passing through even a small lens can quickly ignite a leaf or a sheet of paper. Without a proper filter, a camera's lenses will intensify the sun's light to extreme levels that will quickly destroy internal components.

And if one's eye is at the viewfinder of an unfiltered camera, permanent injury can result in a fraction of a second.

"Every press release that anybody's issuing, at least from knowledgeable sources, is including safety messaging," said Rick Fienberg, a spokesman for the American Astronomical Society. "But of course, no matter how safe you make a car there are always going to be accidents and there will be, I'm sure, some reports of some (eye) injuries.

"But fortunately, even in past eclipses that went over populated areas, the actual incidents of eye injuries was very, very small, and most eye injuries ended up being temporary. But if somebody looks through (a telescope) at the partially eclipsed sun without protection, well, there's nothing we can do about that."

Certified solar filters

So the first item on the casual photographer's eclipse checklist is a certified safe filter. But what sort of filter? Some filters are safe for eyes and cameras, some are safe for cameras but not eyes.

"There's a huge issue with solar filters that people aren't aware of," said Canon photographer and veteran eclipse shooter Dave Henry. "First of all, a solar filter is completely different from a neutral density filter. Solar filters have other transmission characteristics that a typical photographic neutral density filter doesn't have."

He said stacking multiple ND filters, polarizers, etc., to simply cut down the brightness of the sun is not a viable solution.

"Cutting the volume of light down is not the whole story. You also need to minimize the transmission of ultraviolet and infrared. But not all solar filters are created alike. There are solar filters that are safe for viewing and photography and there are solar filters that are only safe for photography.

"So the consumer really needs to do the research on the filter they're buying to make sure it's safe for viewing and photography."

An inexpensive filter, like the DayStar white light filter seen here from B&H, is essential for protecting both eyesight and sensitive camera components from the harsh light of even a partially eclipse sun. William Harwood/CBS News

Several vendors offer inexpensive filters in cardboard frames that will snugly fit on the front end of many common camera lenses, small telescopes or binoculars. Check to make sure they meet the International Organization for Standardization's ISO 12312-2 safety certification recognized by NASA as safe for cameras and direct viewing of the sun.

Such filters work fine for DSLRs. But many point-and-shoot cameras feature lenses that retract into the camera body when not in use and many will retract automatically. Henry advised against taping a filter to any point-and-shoot camera with a fully retractable lens unless the auto retract function can be disabled.

For most point-and-shoot cameras, such jury-rigging is "not recommended because if for some reason you happen to be holding the camera up and you're just looking at the eclipse through the LCD screen and the timer goes out and the lens retracts, it will rip it off the front of the lens ... and it would fry your sensor."

Smartphone cameras? Not so smart

What about smartphones? Henry and Canon photographer Ken Sklute advised against it.

"We both giggle at that only because so many people think a smartphone can handle everything you put in front of it," said Sklute. "They're primarily wide-angle lenses. We're trying to stay away from suggesting anybody use anything like that."

But, he agreed, "some are going to try, and let's pray they have their solar glasses on and they have a filter to go in front of that tiny little sensor that's there."

Other gear and shooting tips

Along with a certified filter, the eclipse photographer should include a sturdy tripod on his or her eclipse checklist. That's because a telephoto lens of some sort is required to capture close-up views of the sun during the partial phases of the eclipse or the shimmering corona during totality.

"A normal (50-mm) or wide-angle (35-mm to 17-mm fisheye) lens will take in the overall scene but will not capture coronal detail during totality, because the eclipsed sun's image size will be tiny," according to the American Astronomical Society's extensive eclipse web page.

"To show a moderately large eclipsed Sun and outer corona, you need a lens with a focal length of at least 300 mm."

When it comes to eclipses, size matters. American Astronomical Society

Veteran eclipse chasers strongly advise practicing on the uneclipsed sun before the actual event and trying a variety of exposure and ISO settings to find what works best.

"Place your camera in manual mode, set the aperture, shoot a range of different exposures (using a solar filter, of course), and see which one produces the most pleasing results," the AAS advises. "You can then use that setting throughout most of the partial phases of the eclipse."

Shooting in manual mode is crucial because most metering systems cannot handle the relatively bright, filtered sun against a dark background. "That's why you need to shoot the camera with a manual F stop, manual shutter speed and manual ISO," Henry said. "And then, of course, make sure there's a solar filter on the front of it. Make sure you turn that auto-turn-off feature off."

A partial eclipse will be visible across North America with the moon covering more than half the sun from virtually any point in the United States. Photographers outside the path of totality must use a certified filter throughout the eclipse.

But totality is another matter, with another set of photographic challenges.

As the moon completely covers the sun, a final few shafts of sunlight shine through rugged terrain on the moon's limb -- Baily's Beads -- before a final flare that gives the vanishing sun the appearance of a diamond ring. Both phenomena quickly fade and the sun's super-heated outer atmosphere, the corona takes center stage, extending from the eclipsed star in all directions like a shimmering halo.

"The last remaining minutes of the partial phases can be quite dramatic and beautiful," writes Fred "Mr. Eclipse" Espenak, a retired astrophysicist and a leading authority on eclipses, on his website. "The crescent of the sun grows thinner as the moon's shadow approaches. The abrupt darkness of totality is stunning and quite unlike you've ever seen. And the incredible solar corona is simply the most awe-inspiring naked-eye sight in all of nature."

Just before and after totality, the eclipsed sun takes on the appearance of a diamond ring as shafts of sunlight blaze through canyon's on the moon's rugged limb. Rick Fienberg/TravelQuest International/Wilderness Travel

The corona is about as bright as a full moon and filters are not needed. Viewers can safely marvel at the view with the unaided eye, through a camera or even binoculars for the two- to two-and-a-half minutes the moon completely blots out the sun. Some viewers wear an eye patch during the final stages before totality to keep one eye dark adapted and ready to see fine detail as soon as the corona appears.

Capturing Baily's Beads, the diamond ring and other brief phenomena before the onset of totality is a challenge for photographers, the AAS says. "Fortunately, the corona is visible throughout totality, and just about any exposure will record some part of the sun's pearly outer atmosphere."

Legendary eclipse observer Fred "Mr. Eclipse" Espenak. His website -- MrEclipse.com -- provides a wealth of useful information on how to successfully photograph a solar eclipse. NASA

The inner corona is about as bright as a full moon, but the outer extremes are a hundred times dimmer and a single exposure cannot cover that entire range. So eclipse photographers typically take a series of exposures using the same F stop to capture as much of the corona as possible.

"At the short end (1/1,000 second or less), only the innermost corona clinging to the solar limb appears," the AAS advises. "At the long end (1/10 second or longer if you can hold sufficiently steady), the inner corona is burned out, but the faint tendrils of the outer corona show up nicely.

"There is no single correct exposure for totality, so your best bet, at any F-stop, is to shoot a sequence spanning the full range from the short exposure you used for the partial phases to the longest exposure you can manage without blurring (perhaps a few tenths of a second)."

As totality comes to a close, viewers must be ready to quickly re-attach filters and/or put their solar glasses back on when the moon's limb begins to brighten, heralding the sun's return.

The AAS offers a handy checklist for eclipse photographers, referring to "second contact" as the moment the moon completely covers the sun -- totality -- and "third contact" as the moment the sun begins to reappear:

"A minute or so before second contact, adjust your f-stop and shutter speed to be ready for second contact.

"When everyone starts screaming 'diamond ring!' take the solar filter off your camera and start shooting. Keep firing until the brilliant diamond is gone, the corona emerges, and you're enveloped in the darkness of the moon's shadow.

"Next, have a quick look around - at the corona, the sky, the horizon, and your fellow eclipse observers.

"Now concentrate on shooting the corona. Run through your exposure sequence from short to long at a fixed f-stop.

"Reset your camera so you're ready to shoot at third contact.

"Now... look up and enjoy the show! The vast range of coronal brightness, the beautiful detail within the corona, and the delicate shading of the sky down to the colors on the horizon are something only your eye can take in. No matter how good your photographs, they won't do justice to the real thing. So make sure you take the time to see totality with your own eyes.

"You'll have a little warning before the arrival of third contact. The edge of the corona opposite where the sun vanished starts to brighten, red prominences may rise, and an arc of red light (the chromosphere) appears from behind the dark lunar limb. Third contact is imminent -- so start shooting. As soon as the diamond ring becomes bright and the corona begins to fade, reattach the solar filter to your camera. Totality is over."

Don't forget to charge your camera's battery before the event and make sure you have a high-capacity memory card to store your images.

Resources for eclipse photography

The internet offers an enormous variety of eclipse photography information, ranging from quick tips and tricks to detailed, step-by-step instructions.

The AAS website includes a thorough photography overview with links to other useful sites with more specific information and details. Photography is just one aspect of the remarkably thorough AAS site, which provides more than enough information to keep even serious eclipse chasers occupied.

Espenak's MrEclipse.com covers cameras, lenses and settings in great detail, including an exposure guide table, sample shots using various settings and still more links to even more detailed information.

Sklute and Henry cover a wide range of eclipse photography topics on Canon's eclipse page, from choosing cameras and lenses, to solar filters, a detailed exposure guide and tips for taking multiple exposure sequences. Some of their advice is Canon specific, of course, but most of the detailed discussion applies to eclipse photography in general.

Still other websites, including Eclipse2017.org, Sky & Telescope magazine and Astronomy magazine, to name just three, offer similarly detailed photography guidance.

But getting the exposure just right and capturing a tightly focused image of the eclipsed sun, or even partially eclipsed sun, is just part of the challenge. Bill Ingalls, NASA's chief photographer, offered a bit of non-technical advice.

"The number one thing I keep telling folks across the agency here is obviously, you can try to make pictures of the eclipse, you can try to do a montage of portions of it and put that all together in one image, as long as you spell out in your caption it's a montage," he said.

"But I think the most important picture, really, is the people around you watching this and reacting to it. I think that's the picture that's really going to be the most important thing here."

In a similar vein, Henry said eclipse watchers should "take a few minutes away from that rectangle of your viewfinder and just appreciate what's happening in front of you ... just the beauty of the eclipse itself."

"As a matter of fact, if this is your first eclipse, sit back and enjoy it with the family. Take a few pictures, but take time to enjoy it.