Safely Photographing the Transit of Mercury and Venus

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When photographing a planetary transit of the sun, be it Mercury or Venus, all of the same safety precautions of solar photography are required, without exception. This is because you are not photographing a planet in the night sky, you are photographing the sun as a planet passes between Earth and the sun.

Images of the transit of Mercury and Venus from NASA/JPL

Photographing the sun poses a very real danger to not only your camera gear, but to your eyes and eyesight. Let’s discuss safety precautions for photographing the sun with or without a planetary transit in progress based on what kind of equipment you are using.

Solar vs. Neutral Density Filters

No matter what type of observing gear you employ, there are two types of filters that work for solar photography, but only one type of filter that works for solar viewing. This is a very important distinction.

Heavy (16-stop) neutral density filters can be used for solar photography but NOT for viewing the sun through a scope or camera’s optical viewfinder. If you are using a mirrorless interchangeable lens camera with an electronic viewfinder, or the live view mode on a DSLR, you may look at the EVF or screen while using a heavy ND filter. Under no circumstances should you look through the optical viewfinder or a camera or the eyepiece of a scope with a heavy ND filter when it is pointed at the sun, because these filters do not filter out harmful radiation—they basically just darken the sun.

If you are employing a solar filter that is approved for solar viewing, you can look through your camera’s optical viewfinder or the eyepiece of a scope, since these filters are designed to block harmful radiation, as well as the amount of light transmitted into your setup.

Another important warning: DO NOT use solar eclipse viewing glasses in conjunction with any magnified optics, be it a telescope, spotting scope, binoculars, or camera. Solar eclipse viewing glasses are for 1x optical viewing with the unaided eye only.

Telescopes

The best way to view a planetary transit of the sun is through a telescope. If you are using a dedicated solar observation telescope, your eyes and camera will be completely protected from the harmful radiation of the sun. If you have a white light telescope (one designed primarily for nighttime viewing) and you are using a filter for solar observing, you and your camera are also protected. Solar filters that ship with telescopes are designed for visual viewing, so, if you are digiscoping through that telescope, your eyes and camera are protected.

If you are using an ND-type filter on a white light telescope, you should never look through the scope’s eyepiece or through an attached camera’s optical viewfinder.

Also, never use a white light telescope’s finder scope when targeting the sun.

Spotting Scopes and Binoculars

The same rules for telescope filtration apply to viewing and digiscoping through a spotting scope or binoculars—ND filters are only OK for photography and electronic viewing and not acceptable for viewing and optical viewfinders. Solar viewing filters are OK for both—just make sure you get the right size for the objective(s) and secure them firmly in place so they can’t accidentally come off.

Superzoom Cameras

Because today’s superzoom or bridge cameras are all digital point-and-shoot cameras without optical viewfinders, you can employ either a heavy ND filter or solar viewing filter to protect the camera. You can safely observe the sun through the filtered camera’s electronic viewfinder or on the rear LCD screen.

Camera and Telephoto Lens

If using a DSLR with an optical viewfinder, it is strongly recommended that you employ a solar viewing filter and not an ND filter, because the ND filter will not protect your eyes when looking through the optical viewfinder. If you are exclusively using live view, or using a mirrorless interchangeable lens camera, you can use either the ND filter or solar viewing filter for protection.

Beyond Your Eyes

Hey, guess what? You are going outside during the daytime to photograph the sun for hours. Wear a hat, appropriate clothing, sunglasses, and at least SPF 30 sunscreen (reapplied often), please!

Stay tuned to our B&H in Space page for more information on planetary transits, eclipses, astrophotography, and all things outer space!

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