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Photographic Exposure of a Solar Eclipse

August 03, 2017

This article was originally published on June 14, 2017 and has been updated to include current information.

Written by Dave Henry and Ken Sklute

Historically Speaking

Since the earliest days of photography, scientists worked at making a successful image of the corona during a total solar eclipse. The first correctly exposed photograph of the corona during a total solar eclipse was made on July 28, 1851 by daguerreotypist Johann Berkowski at the Royal Prussian Observatory at Königsberg (now Kaliningrad, in Russia). The exposure was 84 seconds during maximum eclipse. Numerous attempts were made earlier, but Berkowski’s image was the first correctly exposed image.

A cropped and enhanced version of the original Berkowski daguerreotype of 1851 clearly shows that not only did Johann Berkowski correctly expose his 84 second daguerreotype, he was the first to document the solar flares, known as prominences, emanating from the sun's surface. This daguerreotype became the benchmark for later photographic attempts.

Throughout the remainder of the nineteenth century and on to today, photography has played a significant role in science. Correct exposure though, makes the photograph useful.

Solar Eclipse Phases

There are two parts to a total eclipse. The partial phases occur as the moon begins to partially cover or uncover the sun’s disk. Throughout this phase, you have the full intensity of the sun visible and need an actual solar filter. Not a bunch of stacked neutral density photography filters.  And, you’ll need a solar filter rated for viewing (not just photography) for your camera lens(es), as well as to protect your eyes for any direct viewing, if you’re not looking through the camera. Remember, there are two types of solar filters. One for photography (doesn’t block harmful infrared and ultraviolet radiation) and one that is completely safe for viewing and photography through your camera’s eyepiece. Please re-read the previous article on solar filters.

As the moon progressively covers more of the sun, there will be a point where only a small piece of the bright sun remains visible, and surrounding the moon is a bright ring of light from the sun.  This is sometimes called the “diamond ring effect.”  If you want to successfully photograph this conclusion of the partial phase, leading up to eclipse totality, you’ll need to remove your solar filter and then photograph it.  But be super-careful!  Without a solar filter in place, the direct sunlight — even from just a small segment of the sun — can be damaging.

The light from the sun during the diamond ring effect is very intense so be careful to not look through your camera’s viewfinder to reposition the sun in your frame. Instead, use your camera’s LCD screen.  

About 15 seconds before totality, you can remove the solar filter to photograph the diamond ring effect, and about five seconds before totality, there are still a few tiny rays of sunlight peeking between the valleys of the craters on the moon. This creates what has been named Baily’s beads, after English astronomer Francis Baily.

Cautious photographers may elect to bypass the bright diamond ring effect, leave their solar filter in place through that phase and as Baily’s beads appear, and remove their solar filter from the lens only as true totality appears (when Baily’s beads have disappeared).

Once the moon completely covers the sun, after Baily’s beads, totality has begun and you are photographing the corona. Totality during this eclipse will vary across the continent but will average, on the centerline, about 2½ minutes. At the end of totality, Baily’s beads begin to reappear, leading to the diamond ring effect.

Again, there are two schools of thought on photographing the phases of the eclipse where direct sunlight begins to reappear, after totality — when Baily’s beads become visible again.  Cautious users may be well-served by immediately replacing their solar filter over the lens, and reverting their exposure back to previously-tested exposure settings for sunlight.  This is arguably the safest method to photograph the eclipse after totality.

Experienced eclipse photographers may want to continue to shoot without the solar filter in place, to capture Baily’s beads and the diamond ring effect that follows immediately, as more of the sun becomes visible.  But be aware of the always-present risk of photographing and especially viewing any direct sunlight, without an approved solar filter in place on your lens.

If you do opt to capture the diamond ring effect (with no solar filter in place), once the light of the diamond ring effect becomes very bright, quickly replace your solar filter onto the front of your lens.

From this moment through all the concluding partial phases, the solar filter needs to remain on the front of your lens.

Solar Exposure

Exposing the solar disk can be made in either automatic or manual exposure modes. Depending on the lens and meter mode you use, the possible large amount of black in the viewfinder may create a very overexposed sun disk with any of the automatic exposure modes. Manual exposure mode will usually yield better consistent results throughout the eclipse.

This is because the intensity of the sun isn’t going to change even up to the diamond ring. The sliver of sun you see just before Baily’s beads is still very bright. The only reason the intensity would change is if clouds drift overhead or the sun sinks lower into the west. Our total eclipse in August 2017 will happen midday all across most of America, so we won’t have to worry about a low sun on the horizon.

On the west coast, the altitude of the sun during maximum eclipse (totality) will be about 41 degrees and on the east coast it will be about 61 degrees.

Pre-Eclipse Exposure Testing

To come up with your optimum exposure for all the partial phases (where the sun is fully or partially visible), you have to test your lens/extender and solar filter combination all together, well in advance of eclipse day. To be prepared, try shooting your exposure tests with your solar filter in place in different weather/cloud conditions. That way on eclipse day, if clouds pass by, you’ll be able to check your notes and be ready to make the necessary exposure change. To be sure, periodically check your LCD screen to make sure everything is going according to plan. On the day of the eclipse don’t assume that all locations will have crystal-clear skies!

  

Some people suggest bracketing exposures throughout the eclipse to insure you come away with a perfect exposure to work with. Keep in mind, there’s an illuminated sun disk with little to no detail on it, set against a black background. It’s not like shooting a landscape with highlights and shadow detail to consider. It’s just a disk. The better idea is to shoot RAW. That way you have a three-stop (or greater, depending on the camera) dynamic range to edit with if your exposures somehow drift. The illustration below shows three bracketed sun disk images made in RAW mode. Both of the overexposed images (top-right) were easily edited to equal the correctly exposed first image on the left. The corresponding two images on the bottom-right shows the edits. If you’ve done your homework though, your single exposure will be spot on. If bracketing your exposures will bring better peace-of-mind, go for it. A larger capacity memory card will do the trick.

Field Testing for Perfect Exposure of the Sun

The purpose here is to establish proper exposure for the sun itself, with proper solar filter on the lens(es) you plan to actually photograph the eclipse with. As we said above, we strongly recommend you perform this test several times, in clear midday sunlight, and in varying degrees of hazy overcast skies. First, select the highest ISO your camera is capable of shooting without generating too much digital noise. If you can shoot ISO 800, you’ll be off to a great start.

Then select an aperture you’ll be comfortable shooting based on the maximum aperture you have on your lens. For example, if you’re using a 100-400mm zoom with a maximum aperture of 5.6, you should consider stopping down one f-stop to f/8 for sharper detail. If you’re using a 1.4x tele extender, you’ll lose another stop of light (your lens’ widest aperture effectively becomes f/8), and stopping down one stop effectively makes your new shooting aperture f/11.

Most full-aperture autofocus systems can’t focus through the viewfinder if a lens’ maximum aperture is f/11. But, since you’re focusing manually and ideally using Live View off the LCD monitor, this isn’t a problem. Simply use a focusing loupe, such as from Hoodman™ (or a similar brand), with the LCD screen’s magnification active, and you’ll get a nice crisp focus as you manually adjust the lens’ focus ring.

If you’re shooting a faster maximum aperture lens, such as a 400mm f/2.8, and stopping the aperture down one stop for better edge sharpness, the shooting aperture is now f/4. Even adding a 1.4x tele extender makes the effective aperture f/4, and stopping the lens down one stop for sharper edge detail gives you a shooting aperture of f/5.6.

With ISO and aperture selected for your test images, simply bracket your shutter speed exposures and one of them will reveal itself as the perfect exposure. Make sure you will have a shutter speed fast enough to compensate for the rotation of the earth and freeze the movement of the sun in your viewfinder. Longer focal length lenses magnify the apparent movement of the sun and thus require faster shutter speeds.

Just like we do when calculating the longest possible shutter speed when photographing stars, we can use the same formula for calculating the longest exposure to capture a sharp image of the sun. We need to be at this shutter speed or faster, to avoid possible blur from the earth’s rotation; this has nothing to do with avoiding camera shake from tripod vibrations or similar sources.

The formula for full-frame sensors is 500 divided by the focal length of the lens. For example, if you were using a 500mm lens on a full-frame sensor, the longest exposure we’d be comfortable with would be a one second exposure (500 divided by 500 = 1 second), or faster. To be safe, you’d probably cut that speed in half to a 1/2 second shutter speed and maybe even 1/4 second for extra safety.

On an APS-C sensor camera the rule that is commonly accepted is 350. That same 500mm lens would mean a shutter speed no longer than 0.7 seconds (350 divided by 500 = 0.7), and for insurance you’d probably cut that to a faster shutter speed, such as 1/2 second or even 1/4 second.

Bracketing, Using the Camera’s Auto Exposure Bracketing (AEB) Feature

Most modern digital cameras, even those with fixed lenses, offer some form of built-in exposure bracketing.  On Canon cameras, this is called AEB, for Auto Exposure Bracketing… other brands may use slightly different terminology, but they’ll basically operate similarly.

You’ll usually find a Canon EOS DSLR’s AEB in the red shooting menu, often listed in the menu as “Exposure Comp./AEB” or similar wording.  On the EOS-1D series models, however, it’s usually activated by simultaneously pressing two buttons on the top-left of the camera body, usually with a little icon showing three stacked rectangles between the buttons.  In either case, once an exposure scale appears on the LCD screen, you then turn the Main Dial (up near the shutter button), to tell the camera how different you want each exposure to be.

Canon’s Auto Exposure Bracketing, in spite of the feature’s name, doesn’t limit you to just using an auto exposure shooting mode, like P or Av.  In fact, you can be in Manual exposure mode — which we strongly recommend for eclipse shooting — and still apply Auto Exposure Bracketing.  When you activate AEB in the Manual exposure mode, the camera defaults to varying the shutter speed to change each exposure; ISO and lens aperture normally stay where you manually pre-set them.

The number of frames you can bracket is often changeable in one of the Custom Functions menus. Many mid-range and high-end cameras, such as Canon’s EOS 80D through the top-of-the-line EOS-1D X Mark II, allow up to seven frames of bracketed exposures. With less-expensive models, such as Canon’s EOS Rebel series, there’s still an AEB feature — but it’s often limited to three frames per sequence, no more and no less. Set your camera for the maximum number of bracketed frames. Ideally, your best exposure was found in the middle of the bracketed series.

During totality, with the solar filter removed from the lens, the exposure will be quite different and you’ll want to bracket your exposure as much as possible. If your camera’s AEB will allow you to bracket seven frames, in RAW, bracket in two-stop intervals with your slowest speed at about 1/2 second at ISO 400. If you pre-set your Manual exposure to 1/125th of a second to start with, and then apply AEB with two-stop exposure variance, a 7-frame bracketed sequence should deliver shutter speeds of 1/2 sec., 1/8 sec., 1/30 sec., 1/125 sec., 1/500 sec., 1/2,000 sec. and 1/8,000 sec. Shooting RAW images will allow you to further adjust exposure up to three stops, with your RAW file processing software in the computer after you’ve shot your images.

  

One other feature to see if your camera offers, for AEB shooting:  some Canon DSLRs have another menu option, often in the Custom Functions menu area, to change the order of bracketed shots.  By default, each AEB sequence begins with the “normal” or middle exposure, then switches to the faster shutter speeds, and down to the slower ones.  But if you then view these images as thumbnails in your computer, it’s sort of an awkward experience to see exposures in a sequence jump from normal to super-dark.  So if your camera has the menu option to change AEB Sequence (or similar wording) to something like “minus-zero-plus” or a similar choice, not starting with “zero,” you may want to consider activating this.  Again, not all cameras have this AEB option!

Custom 1, Custom 2 and Custom 3

Many mid-range DSLR models, such as Canon’s EOS 80D, have one or more “C” mode settings on the Mode Dial which Canon calls Custom 1, Custom 2, and so on. The EOS 7D Mark II through the professional 1D X Mark II have an additional C3 setting. These are memory modes that allow you to memorize all your camera settings and save them to one of these three positions. Think of them as Camera 1, Camera 2 and Camera 3, because it’s like having three cameras in one.

Basically, with Canon EOS cameras having Custom shooting modes, set your camera as you would normally — set the regular exposure mode of choice (we strongly recommend Manual mode for eclipse images), any particular shutter speeds, apertures, and ISOs, RAW or JPEG image quality, WB, and even any particular Custom Functions you like to work with.  Then, in the yellow Set-up Menu area, go into “Custom Shooting Mode” (or similar wording), and register what you have set on the camera to the C1, C2, etc. position.

Now, if you simply choose that same C-setting as your shooting mode, the camera instantly jumps to the settings you memorized.  If you need to, you can temporarily shift a setting, like a shutter speed or ISO, as you shoot in one of the C-modes; it’ll normally return to the memorized setting if the Auto Power Off kicks in and the camera goes to sleep.

This feature will come in very handy for eclipse photography because you can memorize all your camera settings for partial phase exposures into C-1 and memorize all your totality settings (including your bracketing sequences) into C-2.

Bracketing sequences are cleared in any of the regular shooting modes, like M or Av, when the camera is turned off. The C-modes have the additional benefit of remembering a bracketing sequence.

RAW vs. JPEG

If you’re really into social media posting, consider setting your camera to shoot Large RAW and Small JPEG. That way you’ll already have a JPEG image ready to send right after the eclipse and you won’t have to go to your computer to convert a RAW file. Otherwise, we strongly suggest shooting Large RAW files.

Shooting individual RAW images, using the single-frame “drive” setting, only applies to the partial phases when the solar filter is in place.

During totality, when the filter is removed to capture the delicate glow of the corona and solar prominences, you will need to bracket as much as possible. The light of the corona diminishes greatly the farther away from the sun it goes. Bracketing is the only way to see this. Stacking these images in layers in image-editing software such as Photoshop® afterwards will produce a spectacular totality photograph showing the corona many radii from the sun. The accompanying illustration is a compilation of 141 images made by three photographers that show the corona extending up to five solar radii.

With AEB set in-camera (we described the process earlier in this article), if you set a Canon EOS camera’s DRIVE setting to either Continuous or Continuous High, you can hold the remote release’s shutter button down, and the camera will fire off a continuous burst of bracketed images, and then stop.  Let go of the button and then press again to repeat.  Firing a bracketed sequence rapidly like this helps ensure that if you later stack images in an image editing program, you won't have problems with each successive image being slightly misaligned due to movement of the earth or moon.

To view and photograph the eclipse, always use Live View on the LCD screen, especially if you’re using a solar filter that’s not safe for viewing and only safe for photography. Live View also locks up the mirror and eliminates mirror movement vibration.

Memory Cards

In order to be able to bracket quickly during totality, you will need fast memory cards so you won’t fill up the camera’s buffer as quickly.

Memory cards have two speeds: read speed and write speed.

The write speed is most important because that’s what keeps the buffer cleaned out. In card manufacturer’s advertising, you will usually see the faster read speed listed. Go to that manufacturer’s website to find the write speed. For SD cards you should have a minimum of 90 MB/s; most recent Canon EOS models will work best with SD cards that are marked as “UHS-I” compliant.  (Be aware that as of spring 2017, no Canon EOS models are compatible with the faster UHS-II card speed standard — so don’t spend extra money on UHS-II cards, unless you have another device that can take advantage of their theoretical extra speed).

For CF cards the minimum is 100 MB/s, for best card-writing speed.  Again, with cameras introduced in the past few years, you’ll get best CF card performance with those cards marked as UDMA-7 compliant — look for that indication on the card and its packaging. Also, use a major manufacturer’s card. Often, they’ll have higher-quality memory and internal components, and provide better sustained performance during extended shooting. Don’t trust this once-in-a-lifetime event on an off-brand card.

Many higher-end Canon EOS cameras, like the EOS 7D Mark II, 5D models from the Mark III upwards, and the EOS-1D X Mark II, have two card slots. This is important. Even though using both card slots will slow down the camera slightly, use both slots if you can afford two memory cards at a time. You can set up the camera to write your RAW + JPEG files to two separate cards at the same time. This serves as in-the-field backup should one of your cards fail. It is highly unlikely to happen if you’re using a major brand card, but do you want to put it up to chance?

The EOS-1D X Mark II has one CF card slot and one very coveted CFast card slot. Shooting RAW to a CFast card is really fast. Buffer size if you record to the CFast slot alone is up to 170 consecutive full RAW files in a burst, and a 128GB CFast card will store over 4,000 RAW images.  Be aware that the CompactFlash card slot cannot sustain this type of burst shooting; the EOS-1D X Mark II is able to shoot up to about 59 consecutive, full-res RAW files to a UDMA-7 type CF card, before it has to stop continuous shooting.

If you’re shooting a camera with two card slots, go to the first yellow Set-up menu and select the first menu selection. Then choose Rec. to multiple. This means your RAW and/or JPEGs are being written simultaneously to two different cards. A great in-the-field backup plan.

Capacity size is important as well because you don’t want to run out of memory in the middle of totality. The EOS 80D will store 840 RAW+ S1 JPEG images on a 32GB card. A 128GB card will store over 3,300 images. That’s not an unrealistic number considering all the bracketing and intervalometer images you’ll be shooting.

The EOS 5D Mark IV will store 640 RAW+S1 JPEG images on a 32GB card. A 128GB card will store over 2,500 images. At least you have something to consider in planning how much you’ll be shooting.

Camera Settings

General camera settings include:

• Setting High-Speed continuous shooting
• Bracketing seven frames at two-stop intervals during totality
• Daylight white balance
• Fine Detail picture style
• Manual Focus by turning off Autofocus on the lens
• Tape down your zoom and focus rings on your lenses
• Make sure your Date and Time are accurate
• Turn off image stabilization on the lens, if you are using a solid tripod
• Set the Image Quality to RAW or RAW + JPEG if you’re doing social media
• You’ll be using Live View during the eclipse so you won’t have to use Mirror lockup
• During partial phases you might consider using the Interval timer (more on that in our article on Totality shooting)
• If you have it, turn on your LCD grid display so you’ll have a center mark to help center   the sun throughout the eclipse
• If you’re going to bracket your exposures, be sure to set the number of frames for each bracketed sequence in the orange Custom Functions menu
• Consider using the C-mode settings for the partial and totality exposure settings

If you have questions you'd like Dave and Ken to address in an upcoming article, email them at: info@theeclipseguys.com.


Click here for more information on photographing the solar eclipse!

SAFETY FIRST: Never look at the sun without accredited and approved solar filtration over your eyes. Permanent, irreversible eye damage and/or blindness can result in seconds. Never point your camera into the sun without an approved solar filter over your camera lens(es). Not using a solar filter at eclipse magnifications will ruin your camera in seconds. Never improvise, modify or use general photography neutral density filters.

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