What is the best lens focal length for photographing the total solar eclipse? Well, there really isn’t a correct answer to that question. There are many factors involved, so let’s outline some options for different types of cameras and budgets.
Above: The Hinode satellite X-ray telescope mission captures the January 6, 2011 solar eclipse. © JAXA/NASA.
Size of the Sun
Most of us think the sun is huge in the daytime sky. Even when masked by clouds, those days we can see the ball of the sun through a thin layer of clouds, the sun looks large. But even though the sun is 864,000 miles across (109 times the size of Earth), the fact that it is approximately 93 million miles away means that it appears to be almost the same size as the moon in our skies.
If you do not believe me, just think about the solar eclipses you have seen photographed in the past. You will see how the moon, during an eclipse, at or near its closest approach to Earth (perigee), blocks out the entire sun. (When the moon is farther from Earth [apogee], the result is a partial blockage of the sun during what is called an annular solar eclipse.) The relative sizes of the sun and moon, and their relative distances from Earth, are what make eclipses so cool for those of us on Earth.
So, the sun is moon-sized in the daytime sky. Got it. But, wait! There’s more.
During the totality portion of a solar eclipse, when the umbral shadow passes over the observer on Earth, the sun’s corona, usually invisible to the naked eye, is suddenly visible and it extends well away from the surface of the sun. So now, the sun and its usually invisible corona are larger than the sun alone.
Field of View
When it comes to deciding what sized focal length lens to use for your eclipse photos, you need to figure out if you want to incorporate the following things in the frame:
Foreground objects and scenery
Only the sun and moon discs
An extreme close-up of a solar prominence
If you want to include some foreground scenery, you should scout your location carefully and select a wide-angle lens that embodies what you want to see in the landscape, while containing enough of the sky to capture the sun during the phases and/or totality of the eclipse. Be aware that, when using a wide-angle lens, the sun will be very small in your frame. Is this bad? Not necessarily; it depends on what type of shot you are trying to get, and many fantastic wide-angle, solar-eclipse images have been captured over the years.
If you have a standard-length telephoto lens, the sun will be slightly larger, but not frame-filling. To fill your viewfinder, you will likely need to go well past a 300mm focal length lens and decide how much of the corona you need to capture. See this graphic that illustrates the relative size of the eclipse for different focal length lenses.
As you can see, using an extreme telephoto lens may cause you to crop out significant portions of the corona. A focal length between 500mm and 1000mm will allow you to capture most of the corona while keeping the sun a good size in the frame.
I recommend you do some research online by looking at the thousands of images of solar eclipses available on photo sites. Many have information on the gear used to capture a particular image, including camera type, lens focal length, and exposure settings.
Focal Length vs. Movement
As you envision your super-telephoto dreams, remember that, when photographing a solar eclipse, you are photographing a pair of moving objects. During totality, you are effectively taking photographs in low-light conditions. The greater the focal length, the more motion blur the sun and moon will have—unless the camera is secured on a star-tracking mount. When photographing the moon, I often aim for a 1/125-second exposure. The above eclipse photograph is a 0.5-second capture requiring a star tracker for decent sharpness. In the absence of a tracker, or with a longer focal length lens, I would have needed to increase aperture and/or bump up ISO to get a shutter speed fast enough to freeze the action.
Included in many DSLR “kits” are a pair of zoom lenses. The wider of the two is usually at or near the 18-55mm zoom range. The telephoto half of the pair often is a lens that zooms out all the way to 300mm. On cropped-sensor cameras, this gives you the 35mm equivalent of approximately a 450mm zoom lens. That is a good focal length for shooting the eclipse because you will be firmly between our 400mm and 500mm example frames in the above diagram.
These lenses are perfectly suitable for solar-eclipse photography with a solar filter, and their reach is long enough to give you a fairly good-sized sun in the frame. However, none are renowned for their optical quality.
Examples of these lenses are any 55-300mm f/4.5-5.6 lens, 75-300mm f/4-5.6 lens, 55-210mm f/4-6.3 lens, or lenses with similar focal lengths and maximum apertures. There are also “all-in-one” zoom lenses with specifications like 28-300mm f/3.5-5.6, 18-300mm f/3.5-5.6, or similar.
In the land of wildlife and sports photographers, there are some extreme telephoto lenses that command extreme prices. Of course, these would be great for shooting the eclipse, but completely impractical for most of us. After all, any lens that comes in its own hardened case is not something you would casually throw over your shoulder and take on a trip or airliner flight. If you want to get one for the eclipse, I won’t stop you. If you want to get two, I’d love to borrow one!
One thing to consider, if you are going to go with one of these behemoths, is that most screw-in solar filters are not large enough to cover the front of these lenses. You will need a sheet of welding glass or Mylar to cover the objective lenses.
Feel free to browse B&H to check these lenses out but be prepared for some sticker shock!
If you want the reach of those exotic telephotos without the price tag or sore back and shoulders, there is a new class of lenses that fills the bill, as far as focal length, but loses a few stops of light in aperture. The advantage to these lenses is that, because they can zoom through the range of the 300mm kit and primes lenses mentioned above, you can alter your solar eclipse compositions to zoom out and zoom back when you want to change the size of the sun and moon in the frame.
Lenses in this realm are like the popular 150-60mm f/5-6.3 lenses and others like a 200-500mm f/5.6, 100-400mm f/4.5-5.6 lenses, and, for Micro Four Thirds a 100-300mm f/4-5.6, 75-300mm f/4.8-6.7, and 100-400mm f/4-6.3 lenses.
For years, I have been a fan of the venerable 300mm f/4 lens. It has the same reach as those kit lenses mentioned above but, as a prime lens (non-zoom), it brings sparkling optics. Also, it is relatively portable, especially compared to its larger maximum-aperture stablemates.
These are not inexpensive lenses, but when compared to the pro-level super-telephotos, they represent a sound value. Like the lenses above, a solar filter is needed.
On the complete opposite end of the lens spectrum from the super telephotos is the classic reflex or mirror lens. Basically, these are catadioptric telescopes with camera-specific mounts. They are small, lightweight, and when compared to almost any other lens, very inexpensive. Mirror lenses, even the ones made back in the day by the big camera companies, were never known for their impeccable image quality. This is, by far, the least expensive way to reach the 500mm focal length. And, like the lenses above, you will need a solar filter.
The last “lens” option for solar eclipse photography using a spotting scope or telescope with a camera is what is known as “digiscoping.” Many scopes allow cameras to be attached to them through various adapters and mounts, or you can simply hold your smartphone or point-and-shoot camera up to the eyepiece of the scope with a digiscoping adapter. One advantage of digiscoping is that you can achieve very high levels of magnification without the exorbitant expense of the super-telephoto lenses I mentioned above.
If you really want to step up the digiscoping game, there are telescopes designed solely for astrophotography—astrographs. These optical tube assemblies do not have viewing eyepieces and are designed to attach cameras for prime-focus imaging of the heavens.
Unless you are digiscoping through a dedicated solar viewing telescope, you must use a solar filter for imaging the sun. Some spotting scopes or telescopes have threaded front openings that allow the attachment of screw-in filters, and others have solar-viewing eyepieces. If your scope isn’t threaded, you can cover the objective lens with a filter sheet or a dedicated solar filter.
If you are shopping for a lens for the eclipse, or already own a lens that you were considering using for the eclipse, I hope this article helps you with your solar eclipse photography planning. Are you an eclipse photography veteran? Share your gear with us. Or, if you have some questions, please ask them below, in the Comments section.