Readers' questions occasionally inspire my columns. A year back, based on a question from Danny Low, I wrote about "Photographing a Supernova," an event that could occur anytime from tomorrow to 100,000 years from now.
A couple of weeks back I got an e-mail from DD-B (David Dyer-Bennet) asking for some advice on photographing the 2017 solar eclipse, whose timing is rather more precisely known and whose path of totality will cross the entire United States from the Pacific Northwest down to the southeast seaboard. It's never too early to start planning ahead for an eclipse, so this column is derived from my reply to his questions.
Do not miss!
Folks, this is a not-to-be-missed opportunity. Anybody who's anywhere on the North American continent should be planning a trip to see this. You really, really shouldn't miss it. You'll just have to take my word for that. I promise that you'll thank me afterwards. There's nothing else like it, and no photograph you've seen has ever done it remote justice, visually or emotionally. Partial eclipses don't count. Partial eclipses are to total eclipses as a McDonald's hamburger is to a filet mignon in a fine French restaurant—entities that theoretically belong to the same class but experientially have nothing at all in common.
A total eclipse is absolutely the most awesome thing I've ever seen. Remember that this is coming from a fellow who's seen a night launch of a Saturn V and stood four meters from red-hot flowing lava. You really may not want to make photographs; you may get a lot more out of the experience just watching. "May" in this case means better than 50% odds, no matter how dedicated a photographer you are.
A total eclipse is mesmerizing.You really may be unable to make photographs. Solar astronomers regularly tells stories about screwing up long-planned experiments the first time they see a total eclipse. Intellectual preparation doesn't work. I knew all of that going to my first total solar eclipse, and I got exactly zero photographs of totality. That was not my intent.
Lots of eclipse-related stuff hasn't been photographed, at least not much nor well. I don't recall seeing a good terrestrial photograph of the lunar shadow on the ground (there are some made by satellites). I don't think anyone has successfully photographed the shadow bands. Those are ripples of light that run quickly across the ground, caused by atmospheric refraction in the very few seconds just before or after totality, when the sun is just a thin slit. I know there are photographs of the landscape by eclipse light. I've got some so-so ones from my first eclipse (I did get photographs, even good photographs...just nothing of totality). The big problem is the same one as including the sun or the moon in a landscape photograph; the luminance range is positively huge. There's enough light. Maybe only 1000th as bright as real sunlight (I don't know, exactly), but much, much brighter than full moonlight. With a moderately high ISO, moderately fast lens, a tripod, and a non-moving landscape, the only real problem is from the exposure range.
Equipment, exposures, etc.
Regarding some of the apparently contradictory recommendations out there for equipment and exposures, not everyone is out to make the same photograph. If you want to capture maximum corona, you're looking at longer exposures although, as these things go, at relatively low magnifications and focal lengths. But, the brightness range from the outermost visible corona to the prominences and chromosphere right around the rim of the sun is easily 10 stops. When I photographed the 1991 eclipse in Baja Mexico, I used Reala 100, because it was the very lowest contrast, longest exposure range film I could find. My best exposure for catching the fullest extent of the corona was one second at ƒ/8 with an 800 mm lens (which produces a solar disk 8mm across). That was on my Pentax 67. That focal length would have been too long for 35mm work; I captured corona out to five solar radii, more than would fit in a 35mm frame. 400–500mm is a lot safer for "full frame" format.
By dint of using color negative film of especially low contrast, I was able to just barely get detail all the way in to the prominences while still holding the outermost corona in my prints (figure 1). Main issue you'll run into when photographing the outer corona with a digital camera is avoiding clipping highlights. (Yes, there are people out there doing some very, very clever single- and multi-image processing on eclipse photographs. Whole different topic; we're not going there this time.)
You wouldn't likely need to use that great an exposure. For one thing, in seven years optimal camera ISO is going to be at least 200 and it might be 400. For another, that exposure was pushing into the reciprocity failure region of the film for the dimmest parts of the scene. Not by a lot, but I was losing at least one stop of shadow speed, maybe more.
All told, I'd be surprised if you'll need an exposure longer than 1/4 second atƒ/8 to capture huge amounts of corona. For near-Sun detail, your exposure times would be more like 1/60–1/250 of a second...said with the caveat that the brightness of the corona is not predictable. The near-surface brightness is pretty standardized, but the brightness and clarity of the corona away from the surface not only depends upon the actual coronal activity, which can vary hugely, but also how clear and dark the atmosphere is that day.
Do you need a tracking mount? The sun is moving at 1/14,000 radian/second. If you're using a 500mm lens, that's 1/28th mm/sec in the sensor plane. With a 1-second exposure, that's roughly the "circle of confusion" you'd use for acceptable 35mm work, and I used the same thinking for determining my maximum exposures. The prints look just fine. If you're using 1/4 second, as I'm guessing you would be, that's 1/100 of a millimeter in the sensor plane. That's plenty, plenty sharp!
It's not pixel-level sharp, though, and many of the recommendations you'll read are from people thinking like astronomers. They're trying to figure out how close as they can get to seeing- and diffraction-limited performance. They may also be working at considerable higher magnifications. With decent seeing and a large enough aperture (at least 150mm and preferably 300mm) on a diffraction-limited scope, one should be able to reliably resolve down to better than 1/200,000 radian. That implies relatively short exposures. Hence the potential need for a tracking mount.
But there's a bigger, practical reason for using a tracking mount. It will keep the sun centered in the frame for the entire eclipse! For the serious solar photographer, it's one less thing for them to worry about. Once the camera rig is pointed at the sun, they don't have to keep adjusting it. As I intimated above, the fewer fiddly bits one has to deal with during an eclipse the better the chances of getting decent photographs and enjoying the eclipse.
Watch in awe
Still, my main recommendation would be to go mentally prepared to wind up just watching the most amazing spectacle on all of the planet Earth.
Ctein's regular weekly column appears on TOP every Thursday morning.
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Original contents copyright 2010 by Michael C. Johnston and/or the bylined author. All Rights Reserved.
Featured Comment by Christian Dummer: "I can't but agree on the almost mystic nature of totality. I had the chance to see the Nov. 1994 eclipse in Putre (northern Chile). I was 18 at that time, and still have vivid memories of the enthralling display...in fact, I was so impressed by the experience that I made a resolution to watch the next total eclipse I could.
"So Ctein's timing with this post could not have been better! Right now, I'm only days away from a weekend trip to Easter Island (fortunately just a 5-hour flight away from my hometown, Santiago de Chile) to watch the July 11 eclipse that will be visible in the Southern Pacific and a small portion of Patagonia. Wife's coming along, equipment is all set, and all what's left is hoping for good weather. So thanks for the recommendations, they will certainly come in handy much earlier than 2017!"
Featured Comment by Nathan deGargoyle: "From my sub-teenage memories. It was the late '60's on a Swann's Hellenic Cruise. We were on a tour of Athens and had got to the Theatre of Dionysos. The lecturer had done the usual, got us to sit on the back row then spoke in an ordinary voice to show how good the acoustics were.
"Then he said 'There's an eclipse due in about half an hour. If we stay for it we'll have to miss the museum. Can we take a vote?'
"It came out about 60/40 for staying.
"So we sat in this ancient Greek theatre. Firstly the birds who had been calling loudly went quieter and quieter until there was silence, broken only by the passing traffic noise. Then it started to go dark, like a cloud had moved over the sun. They passed out bits of smoked glass but looking at the sun wasn't the point. I have never had a more eerie experience, all the better for it being totally unexpected (and probably even better still for being age 10.)"