Photographing the Sun can be perfectly safe, as long as you take the proper precautions. You can use these techniques to photograph the November 11th transit of Mercury.
Photographing the Sun is not usually the first idea that pops into your head when you hear the word astrophotography. But why not? The Sun is, after all, a star — the closest one to our planet. It’s sobering to think that our Sun is an average citizen of the celestial host we see overhead each night. It's just a bit more up close and personal.
Although there are several methods for photographing the Sun, let's focus this month’s technical discussion on white-light solar imaging. White-light solar photography means that any filtering we use is intended to reduce the amount of light, rather than isolate any particular wavelength (such as when using a specialized solar hydrogen-alpha filter).
White light solar imaging does a great job of showing sunspots and facula, and is the easiest and most economical method you can use to photograph next month’s transit of Mercury on November 11th. Hey, you didn’t think I just pulled this topic out of a hat did you? White light is really what the Sun looks like assuming you could look at it without going blind. Most any color camera, such as a DSLR or mirrorless camera can capture a pleasing white light image, so you can use pretty much any camera you already have.
Solar photography is easy but great care must be taken when pointing any telephoto lens or telescope at the Sun. I don’t need to tell you, it’s really hot and it hurts just to look directly at it! A big light-gathering optic captures all that energy and focuses it down to a smaller area. I’ve often said in astrophotography that more light is always better . . . this might be the one time I'm wrong! Focused, unfiltered sunlight will almost immediately burn or melt anything at the focal plane. This includes camera shutters, sensors, your hand, or God forbid, human eyeballs.
When imaging the Sun, the trick is to simply reduce to a safe level the amount of light from the Sun that is reaching your sensor. Many of the cameras damaged during the 2017 solar eclipse were the result of bad advice — some had stated that a strong neutral density filter on the front of the camera lens would sufficiently reduce the light entering the lens or telescope. This is not only wrong, but extremely dangerous.
There are several inexpensive white-light filters that fit over the front aperture of your telescope or camera lens. My personal favorite is Baader AstroSolar film. Any of these certified solar filters will reduce the amount of light entering your optical system by 99.999% — a 100,000× reduction in intensity — and make photographing the Sun a safe and easy activity, similar to photographing the Moon.
Years ago, I purchased a bulk roll of AstroSolar film to make my own customized solar filters. Taking care not to damage the material, you can make a full-aperture filter with the film material for your camera lens or telescope with a little cardboard and tape. Craft night! You can also use it to make safe solar glasses or filters for your binoculars. I simply used a rubber band to hold the foil over the front of a telephoto lens, and it worked great.
Most of my tips for imaging the Moon apply equally to white-light solar photography, such as locking up the mirror in your DSLR. A Sun-specific tip is to bring a light-blocking blanket along to put over your head. Out in bright sunlight it's very difficult to see the LCD on the back of your camera. When shooting the Sun, it's best to bracket your exposures, so you can ensure that at least one of them is properly exposed. It's also better to underexpose a bit, as it's very easy to lose contrast on sunspots or facula features. Trust the histogram — the more spread out it appears the better, even if it's a little darker (more to the left) than where you think it should be.
Photographing the Sun can be done safely, and cheaply, but be sure and have a sober respect for what you are doing. Like playing with fire, a moment of carelessness or inattention could end in disaster. When using a front aperture filter, be mindful of the wind as well as curious pets or children, who have no idea how important that little bit of shiny foil is. Stay safe, have fun, and good luck on November 11th!