What is a Solar Corona?
The smooth tendrils of light seemingly extending from the dark side of the moon are solar coronae. In simple terms, the sun has many layers of the atmosphere. The outermost layer is called the corona. We can’t really see the corona because of the sun’s bright light. However, during a total solar eclipse, the moon blocks most of this light out, and the corona becomes visible (NOT to the naked eye) for a brief period of time.
But to truly understand this fiery phenomenon, we need to get some of our basics right. The sun gets its energy from an enormous nuclear fusion at its core. This nuclear activity has enough energy to last more than five billion years. The Sun itself is made up of plasma, the fourth fundamental class of matter. Plasma is essentially a super hot concoction of electrons and ions. The movements of these ions give rise to the Sun’s magnetic fields.
These magnetic fields are important. They have a few notable and crucial effects on our lives too. But we will get to that in a moment. So, the sun is made up of plasma. The round ball that we see from Earth is the photosphere. What we see in the picture above are the regions beyond the visible photosphere of the Sun. One of these regions is the Corona.
Interestingly, the Corona has a much higher temperature than the surface of the sun. The exact reason behind how the Corona gets so hot, given its distance from the core, is a debated one. The prevailing theories indicate that it could be due to a process known as magnetic reconnection. In a nutshell, magnetic reconnection is a physical process that converts magnetic fields to energy.
Coronas are a combination of some of the most visually appealing phenomena in the universe. Solar flares and coronal loops have always been of interest to space enthusiasts. Solar winds also generate from the corona and are extremely powerful. They can destroy our communication networks. Thankfully, Earth has a magnetic field that protects it from these magnetic winds. Mars didn’t have one and hence it was stripped of its atmosphere.
How can you view a Solar Corona?
Watching a solar eclipse with naked eyes will damage your eyes. That’s certain. It is very important to exercise precaution when trying to view a solar eclipse. During the period of totality, for a fraction of the time, you can theoretically observe the eclipse with the naked eye. But during the onset of the partial eclipse until totality and then after totality, till the moon steers clear of the sun, you are supposed to wear solar eclipse glasses.
Why is it hard to capture a Solar Corona?
The image you see above is not a single image. It is a combination of 40 images and it has been cleaned out using digital image processing software. It is not easy to capture a solar corona in all its glory, solar flares and all, using regular cameras. It’s not even easy to do it with most DSLRs. However, with DSLRs, you can shoot multiple pictures in RAW and then combine them to get something like the image above.
One of the main reasons that we need to shoot RAW and more than one image is Dynamic Range.
When you walk out into a sunny day. Just stand still and process what you are seeing. The sky is blue and bright, the clouds are fluffy and perfect, and you can see the city’s skyline. Additionally, in the foreground, you can see everything on the street, the supermarket’s name and all the pedestrians. In short, this image in your brain is very well lit. Nothing is under-exposed or over-exposed. Hence, we can say that the dynamic range of your eyes is pretty impressive.
Unfortunately, the camera’s can’t do that. There are always bright, over-lit areas and underexposed shadows that you need to correct in post-processing. And that is done by taking multiple shots and combining them.
Things you need to perfectly capture a Solar Eclipse with the Corona
Apart from a camera with a high dynamic range here’s what you need to capture a solar eclipse or solar coronae
A good telephoto lens
A telephoto lens, as opposed to a wide-angle lens, offers a zoomed-in vantage of the subject. It is the obvious choice for photographing a celestial body. In fact, the more focal length you can get, the closer up you can get to the sun. But note that as the focal length of your lens increases so does the size of the lens.
In my personal opinion, Canon’s 70-200 F2.8 is the best telephoto lens available on the market. Though it is pricey, the results are unmatched by any other lens on the market. However, you can use any decent telephoto lens and get a pretty good shot. Canon’s 75-300mm is a great deal and an excellent addition to your lens collection if you are on a budget.
As for Nikon users, the Nikon AF-S 70-200mm f/2.8G ED VR II is just as good as its Canon counterpart. Whereas the Nikon AF-S DX 55-300MM f/4.5-5.6G ED VR is economical and does the job quite well. If you are a Nikon owner and want the cheapest option available, you should check out this lens from Tamron.
A lot of astrophotographers use telescopes too.
Price range: 70-1950USD (Canon), 400-2800USD (Nikon), 120USD (Tamron).
A converter adds some zoom to a telephoto lens. Usually, it increases the focal length of an existing by a factor of somewhere between 1.5x-2x. It’s also called an extender or a multiplier. It’s not necessary to have one of these but if you like to get in a little bit closer, a teleconverter is always a cheaper option than buying a new lens.
But there is a decrease in sharpness, incident light, and speed.
Price range: 380 -450 USD
A solar filter is very important while photographing the solar eclipse. The sun is the brightest object that you will see in a lifetime. To picture it, you have to block out all that light. Moreover, beyond the visible rays, sunlight also includes UV and IR rays. If you point your camera towards the sun without a solar filter, there’s a good chance that you will end up frying the sensor. These can be of various types.
Solar filters can be of various types. You can get sheets of filter, screw-on filter, step-up rings or if you have the cash to splurge, an intermediate filter.
These screw-on filters from Astromania are safe and easy to use, just make sure you get the diameter right and you will be good to go.
Please note that you should not use ND filters in lieu of solar filters. It’s just not the same. And do not use the optical viewfinder even with the solar filter on. Use your live view mode.
Price range: 20-70USD
A sturdy tripod
When you are photographing anything with a long focal length lens, even the tiniest of disturbance to the camera will get amplified resulting in a blurry photograph. A sturdy tripod is always a good investment. If it has a hook to attach a bag of weights, you can use it to ensure a higher level of stability.
Price range: 60-300USD
A remote shutter release
For the same reason as above, another necessary tool to capture the solar corona is a remote shutter release. This nifty device allows you to engage the shutter without having to touch the camera. So your long exposure shots don’t get disturbed by your fingers fumbling for the shutter. You can use a wired remote or a wireless one, as long as it does its job, it doesn’t matter.
Some cameras can also be controlled using proprietary mobile apps. However, in my experience, these apps are laggy and not responsive enough to make quick changes. You can also use the timer function in your camera if you can’t get hold of a remote.
Price range: 20-40 USD
The sun moves about one solar diameter every two minutes. And when you are viewing a solar eclipse, every moment is precious. An equatorial tracker pans on its own corresponding to the sun’s path. So you don’t have to do it manually every few minutes and you are essentially shooting hands-free. It’s not extremely necessary to have this with you though. These can get a bit pricey so try to rent it if you can.
Price range: >300 USD
Once you have all the tools necessary to photograph the event, your mind will be at a lot more peace, which is necessary during once in a lifetime moments.
How can you photograph a Solar Eclipse and the Solar Corona?
The thing you should always know about photographing the sun is that there is more light coming in towards your retinas than you think. Apart from the light in the visible spectrum, which by itself could damage your eyes, the sun’s radiations in the UV, IR range can also adversely affect your eyesight. So make sure you have the right solar filters on your lens before you photograph any scene that has the sun in it.
Also, you should remember that your optical viewfinder is off-limits when photographing the sun. Even if you have a solar filter, it’s safer to view the image on your screen.
Once you have taken all the safety measures and readied all your tools, you should start setting up your shot. Depending upon the type of photograph that you wish to take, there are a set of standard rules that you should follow. Or, if you have practiced enough, you can chuck these rules right out of the window and stick with what you know. However, if you are a novice, you might want to stick to the rules to make sure you don’t miss out on these once in a lifetime shots.
Case 1: A close-up shot of the eclipse, before and after totality
So you have a tripod, a remote shutter release and a solar filter attached to your lens. Keep an aperture above F4.0. Now it all comes down to composition and exposure control. Always shoot in RAW. That’s a no-brainer. Don’t get in too close, you can always crop the image in post-processing. The period between the start of the eclipse and post-totality can be captured at high shutter speeds because there’s gonna be a lot of light. Depending on your solar filter figure out a range of usable shutter speeds. Capture multiple shots with different exposures in quick succession. You can combine these shots later to get an evenly lit photograph with all the details.
Case 2: Totality and the solar corona
This is the moment everyone’s been waiting for. The highlight of the eclipse. And your chance of getting your money shot. Just a few seconds before totality, there will be a rapid fall in the ambient light for obvious reasons. Get your remote shutter ready, take off the solar filter and dial down your shutter speed. DO NOT get in too close because you could miss out on the beautiful tendrils of the corona. Take an underexposed shot, a normally exposed shot and a slightly overexposed shot.
Case 3: Wide angle
If you have planned your expedition properly by checking the path of totality and picking out a scenic spot, you should definitely keep a wide-angle shot on your to-do list. A picturesque foreground with a glorious eclipse, partial or not, is an excellent way to tell a story. It goes beyond capturing a dark backlit disk and tells the viewer about the effect the celestial event had on the landscape.
To shoot a wide-angle shot of the eclipse you’ll need a wide-angle lens. Something around a 24mm would be great. Set up the shot in the same way as we discussed above. But you should know that the eclipse will appear smaller than in real life because of the way wide-angle lens profiles work. But you can always correct that in post-production.
It’s quite understandable that you will feel a rush of excitement during this event. It’s one of the most awe-inspiring moments that you will have witnessed. So try to take that in. Try to soak up the atmosphere. Look around you, look at the people, their expressions and the look of utter bewilderment in their eyes as they try to process the immense beauty of the totality. Notice how the light changes over the landscape, take a moment to appreciate the moment with your loved one. Once you’ve done that, you can proceed to take your pictures. Oh and don’t forget the glasses. DO NOT FORGET THEM.
Sources and further readings
- Reputable Vendors of Solar Filters & Viewers – American Astronomical Society
- Solar Corona – Wikipedia
- Awesome Corona Wallpapers – Miloslav Druckmüller
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