Types of lunar eclipses
Eclipse photography is a very special type of astrophotography. Eclipses are very rare phenomena, and come in four main types. Annular, hybrid, partial, and total eclipses. An annular eclipse is very similar to partial and total eclipses in that the moon is covering the sun. However with an annular eclipse, the moon is at the far end of its orbit. Therefore, it appears slightly smaller than the sun, whereas in a total eclipse, the sun and moon appear to be the same size. Because the moon looks smaller in an annular eclipse, it doesn’t completely cover the sun. The result is a ring of light created by the sun. A hybrid eclipse is where observers on the Earth are treated to an annular or total eclipse, depending on your location. A partial eclipse is what most people will see. The moon will move to cover the sun, but incompletely. And for the lucky ones along the path of totality, a total eclipse can be seen. A total eclipse is when the moon completely covers the sun for a couple of minutes. Occasionally, sunlight spills out from craters, creating bright jewel-like effects, and the solar corona can be seen and photographed during totality.
Never look at the sun!
First, it’s very important to mention that you should NEVER look directly at the sun even with your eyes unenhanced. With a camera optical viewfinder, telescope, or lens, the danger is much greater. Looking through an optical viewfinder at the sun could burn the retina of your eye and cause blindness. Even covered to 90%, the sun’s remaining 10% light can cause permanent damage to your eyes when viewed through a lens. In addition, the optics of your lens and the image sensor itself are at risk. So remember to have a solar filter in place while composing your photo, even before the actual eclipse. If you’re unsure as to how well the filter is working, use a piece of paper to allow light to be projected from your optical viewfinder to that paper.
Solar filters come in a variety of powers and prices. Solar filters start at around 10 stops of light reduction, which reduces the amount of light received by a factor of 1000. Each stop is a halving of the amount of light, equivalent to reducing your aperture (f/stop) by one step, or a single increase in shutter speed (1/250th to 1/500ths of a second). So 10 stops would be reducing your aperture from f/1.0 to f/32. A 1 second shutter speed becomes 1/1000ths of a second. As you can see, this is a serious decrease in the amount of light, which is exactly what we need to take eclipse photos.
You can also use stacked Neutral Density filters if you don’t want to purchase a dedicated solar filter. Just so we’re clear, a solar filter IS a neutral density filter; it’s just so strong looking at the sun is all it’s used for. Most neutral density filters only cut the light by 1/4th to 1/16th or so. If you do any landscape photography, they’re an excellent tool to have around. ND filters let you take long exposure pictures without the entire scene being too bright. But the nice thing about them is that they can stack on top of each other. So if you have an ND 6, ND 4, and ND 2, you’ll still gain 12 stops of light reduction. But there’s a very important difference to point out: ND filters only filter VISIBLE light, NOT UV or infrared light. This means it’s still not safe to look at the sun directly, even with your ND filters on. Both of these light types can cause damage to your eyes; and the danger is even worse as your eyes won’t even see the UV or feel the infrared heat. You won’t know until your retinas start to cook. And you don’t want to keep the camera continually focused on the sun for the same reason. Heat is just as dangerous for your image sensor as it is for your eyes. So if you have stacked ND filters, briefly point your camera at the sun, and compose your image by project your view onto a piece of paper or using the LCD live view. But don’t forget the heat remains a risk to your image sensor.
A remote shutter and tripod are also important tools for eclipse photos. Both eliminate tons of blur that can happen when you press the shutter or jostle the camera slightly. Later on, once you start photographing the sun’s corona (total eclipse only), you’ll need to take multiple exposures without moving the camera. A remote shutter and tripod are the only way to do this. If you don’t own a remote shutter, most major digital camera manufacturers have apps to help you. You can use a WiFi or NFC connection to sync to your smartphone or tablet. Then without touching your camera, you can take photos and even send them right to your smart device.
A total eclipse is the photo everyone wants to capture. The moon is completely covering the sun’s disk and you have a chance of capturing the corona of the sun. The corona is the outer atmosphere of gas and charged particles streaming from the sun. The part closest to the sun appears as bright as the full moon during a total eclipse. The outer edges are hundreds to thousands of times fainter the farther you get from the sun. At this stage, you’ll need to remove your solar or ND filters, as the entire sun is being hidden by the moon. Then, you’ll need to take a series of photos at a variety of shutter speeds. Start with 1 second and then reduce it 1 stop each time all the way to 1/1000th of a second. You’ll need to then take your images and combine them using Photoshop, Lightroom, or a similar program. The resulting composite image will show all of the details of the inner and outer corona.
Solar eclipses are relatively rare phenomena and should be planned for well in advance. But the images one can get are well worth the planning and travel needed. All of it leads to an event that lasts at most 7.5 minutes but will inspire lifelong memories. Don’t forget the right type of solar filter and proper technique to avoid damaging your camera or your eyes. Happy shooting!