You may have seen an eclipse or two and are now motivated to become an astronomy hobbyist. The great April event is the perfect opportunity to start working on your astrophotography skills.
But do you have the ideal camera for the task?
The first option that may come to mind is the one included in your cellphone. Modern cellphone cameras are excellent for close-range images, but once you want to zoom in, the image becomes pixelated and loses its resolution. And even with a sharp image, any size beyond a phone background will destroy the clarity. Point-and-shoot or compact cameras are easy to use, but more often than not, they lack the ability to swap out lenses for different shots and connect to a telescope.
If you want a top-quality image of the April eclipse, the best options are either a digital single-lens reflex (DSLR) or mirrorless camera. Both vary in construction and price, but not in their sensors nor core features. Here’s how to choose the right one, even on a budget.
Choosing an image sensor
Not only do DSLRs and mirrorless cameras have larger sensors (or chips) than other cameras, they have two different chip options.
The first is a full-frame sensor. Professional photographers demand these because they capture a wider scene and collect more light than smaller sensors, producing a higher signal-to-noise ratio and improving the overall quality. Nighttime astrophotographers treasure this feature because it means they can shoot at high ISO numbers — which can lighten or darken the image — without introducing noise to the image.
The second type of sensor is the Advanced Photo System type-C (APS-C) sensor, which has an image aspect ratio of 3:2. This chip measures 1 inch by 0.7 inch (25.1 millimeters by 16.7 millimeters). Compared to a full-frame chip, an APS-C sensor crops the image so the subject occupies more of the frame, resulting in a narrower view. The difference changes the effective focal ratio of a lens by a factor of around 1.6.
Another big difference is that full-frame models (and mirrorless cameras, in general) are more expensive. In the case of photographing eclipses, you’ll be concentrating on the Sun, which is a ½°-wide circle of sky, plus the corona, which may extend 2° or 3° across. Spending $2,000 for a full-frame-chip camera is unnecessary when a $500 model will do.
At the end of the day, cameras with APS-C sensors produce top-of-the-line images of eclipses, and may be best for both your budget and your broader use.
Megapixels: More isn’t always better
Camera chips are covered with tiny light-collecting elements called pixels (the smallest units of a digital photo), arranged in rows and columns. Manufacturers measure a camera’s resolution based on the number of megapixels, or MP, (each MP equals 1 million pixels) on its chip. If a certain camera’s chip contains 4,000 rows and 3,000 columns of pixels, then it has a total of 12 MP (or 12,000,000 pixels).
It may be logical to think that a sensor with more MP will have higher resolution. However, this isn’t always true because not all pixels are the same.
Pixels can come in different sizes. For instance, cellphone sensors are only a fraction of the size of a full-frame sensor. To pack millions of pixels onto cellphone sensors, manufacturers use much smaller pixels than those in DSLRs. As pixels become smaller, their ability to collect light decreases. The larger pixels used on DSLRs capture more light, produce better color, and have less noise.
Beauty is in the lens of the beholder
The camera lens is the vital key that determines the camera’s true strength. If the lens is low quality, no amount of processing or editing will help.
A larger width means more light gets to the sensor. The focal ratio — also referred to as aperture setting or f/stop — of a lens determines how wide it can open. A smaller f/stop means the aperture can open wider. For example, an f/4 lens will produce a brighter image than an f/18 lens. Despite photographing the Sun, incoming light should still be considered. During totality, the strength of the Sun’s light will be only one-millionth that of the full disk.
There’s another critical aspect of focal length to consider on eclipse day: The larger the number, the larger the Sun will appear in your photo. To figure out its size, you’ll have to determine your camera/lens combination’s field of view (FOV).
The equation you need is: FOV=2*arctan(0.5*s/f)*180/π. Don’t let the equation intimidate you. To calculate your FOV, take the chip dimension (s) and divide it by the focal length (f) of the lens. Both s and f should be in millimeters. Next, divide that number by 2. Then, find the arctangent (or inverse tangent) of that number — this can easily be done with most smartphones or using Google’s online calculator. Finally, multiply that number by 114.6 (the value of 2*180/π). Now you have your field of view expressed in degrees.
This formula is one-dimensional — in other words, it gives only x or y, the width or height of your chip. Thus, for a 2D FOV, you’ll have to perform this calculation twice. If you’re attaching your camera to a telescope, its the same equation. The scope’s focal length is either on the tube or the ring that secures the front optic. If not, look in your instruction manual.
Eclipse considerations
I suggest finding a new mirror-less camera or a used Canon camera with an APS-C sensor. Set the sensor size to 12 MP as your minimum. Then select a lens that will give you the final Sun size that you’d want.
Always take the proper precautions to avoid eye or camera damage. And a bit of advice: Try focusing on the Moon while following the solar eclipse through its phases (the Sun might be too bright and too small).
When you get some images you’re proud of, send them to photoeditor@astronomy.com. They just might appear online or in print.
