Photographing the Transit of Venus

By now, most of you have heard about the transit of Venus that will occur on Tuesday or Wednesday. (If you haven’t, I’d like to come and visit you sometime. I enjoy spelunking!) Venus transits are among the rarest of celestial events, occurring in pairs eight years apart, but with the pairs separated by over 100 years. The last transit occurred in 2004. After Tuesday, the next Venus transit won’t occur again until 2117. I missed photographing the 2004 event and there’s a pretty good chance that I won’t be around in the 22nd century, so I’m especially excited about pointing my camera at this one.

What exactly is a transit? First, it has nothing to do with night photography. (Yes, I do occasionally photograph during the day!) A transit is simply one body passing in front of another, similar to an eclipse. With the transit of Venus, the planet passes in front of the sun. But don’t expect it to be anything like an eclipse, with the sky darkening. The apparent diameter of Venus will be about 32 times smaller than that of the sun, so it will appear only as a tiny black dot.

The amount of time it takes for Venus to pass across the face of the sun varies. The 2012 transit will last nearly seven hours. Not everyone will get to see the entire event, however. In the U.S., the transit occurs on the 5th, beginning at about 6:05pm (EDT). For U.S. viewers, the sun will set while it is occurring. For viewers in much of Europe, east Africa, and eastern and southern Asia, the sun rises on the 6th with the transit already in progress.

Google “Venus transit” for a wealth of information about the event. Here and here are two good sites. Sky & Telescope’s site for the transit provides some good information for viewing, as well as photography info. In addition to scientific and historical information, these sites give information for safely viewing the event.

Of course, you should never look directly at the sun without proper eye protection. You can use special solar-viewing glasses, #14 welder’s glass (must be #14 or greater and glass—not the resin type), or special solar filters. If you photograph or view through telescopes or telephoto lenses, you MUST attach a proper solar filter to the FRONT of the scope or lens. The sun shining through an unfiltered telescope or telephoto lens can generate enough heat to melt plastic, so just imagine what it can do to your eyes!

I won’t be using a telescope or long telephoto lens to photograph the transit. Come Thursday, the Internet will be flooded with photos that all look the same—a big orange ball with a tiny black spec on it. (Most people who photograph the sun through telescopes use solar filters that render the sun as orange or yellow instead of the white color that it actually is when high in the sky.) I decided not to buy an expensive solar filter just to make photos that look like everyone else’s. I’m going to try something a little different and use wider-angle lenses to photograph the event and include other elements in the scene besides the sun.

I love to photograph sunstars, so I figured I’d try that technique during the transit. Since I didn’t shoot the 2004 event, I have no idea how well it will work and what the resulting image will look like, but I’m hoping it will look something like the conceptualized image I’ve posted here. The technique for shooting sunstars is very simple. Point your camera at the sun and shoot with a small aperture, say f/16 or f/22. The diaphragm blades in the lens’ aperture will automatically create the star effect.

Sunstar over New River in West Virginia

A conception of what the transit of Venus might look like in a sunstar photograph.

 

While the basic technique is simple, there are some things to keep in mind. First, remember that you’re looking at the bright sun through a camera lens, which is really not a good thing to do. NEVER look directly at the sun through the lens; look off to the side to compose. I like to hold the depth-of-field preview button down while composing because it drastically lessens the sun’s brightness. And it’s a good idea to handhold the shot. You don’t want the camera sitting on a tripod where you might be tempted to look through it more than necessary. Also, because the sun is moving across the sky, you’ll find that you have to reposition the tripod constantly. Since you’re shooting in bright light conditions, the shutter speed is usually high enough to allow for sharp handheld exposures. If your camera has a Live View feature, use that to compose so you don’t have to look through the camera.

I can hear the safe-solar-viewing police knocking at my door, so let’s talk about this in a little more detail. Understand that I’m talking about WIDE-ANGLE lenses here—24mm or wider. If you compose with the sun off to the side, you can look through the viewfinder to the opposite side and not have the sun directly hitting your eye. Think about it; nature photographers do this all the time when the sun is in the frame. In fact, we often do it when we shouldn’t, with longer focal-length lenses that increase the possibility of direct sun exposure. To be safe, if the sun is in the scene, never look through the viewfinder with a lens having a focal length longer than 24mm. Use Live View or don’t take the picture. Also, unless you have a proper solar filter attached to the front of the lens, I wouldn’t even point a lens longer than 300mm at the sun, much less look through it.

Exposure is pretty simple with sunstars. You want the exposure to be a little under to cause the sun to stand out and it usually looks better to have some of the other elements in silhouette. Most cameras do a pretty good job with this on the automatic setting. Choose an ISO of about 400 and let the camera pick the shutter speed. The camera sees that bright sun and tries to compensate by underexposing, which is what you want. You want the fairly high ISO to get a shutter speed fast enough to handhold. Typically, with an aperture of f/22 and ISO of 400, the shutter speed will be in the 1/250 to 1/500 second range for a nicely exposed sunstar. Automatic exposure aside, I never let my cameras do all the thinking for me. I always check the histogram to make sure I have it right. A good histogram for a shot like this will show clipping in both highlights and shadows. Remember, it is impossible to have any detail in the sun, and there is no problem with clipping some of the shadows in the silhouetted portion. Actually, with sunstars, you can judge exposure pretty good with the LCD, at least with the Nikon D700 that I use.  

Air quality plays a big role in how defined a sunstar looks. Ideally, you want the clearest air possible. I’m just hoping it isn’t cloudy on Tuesday, but the forecast for western North Carolina isn’t looking too promising. Flare can be a big problem, whether the air is clear or not. One major contributor to flare is the use of zoom lenses. Zooms have a lot more glass elements in them than do prime lenses. Light bouncing off that glass contributes heavily to flare. I shoot with zooms almost exclusively and have learned to watch the composition carefully. Changing the position of the sun ever so slightly can make a huge difference in the amount of flare. Any filters will act just like another glass element, contributing to the flare, so be sure to remove them.

Since the sun sets while the transit is in progress (for North American viewers), I’m hoping that when the sun is close to the horizon it’s intensity will diminish and become safe to look at. You know, the orange sunset sun that nature photographers love. If that happens, I might try a few shots through longer lenses of about 300mm or so, but still including other elements in the scene.  

Since the transit lasts for several hours for most viewers, it provides a great opportunity for experiencing it in a number of different ways. You can photograph it in all manners, view it directly with safe filters or viewing glasses, project it onto a white card (you know, like you would an eclipse), and even watch it on the Internet. Slooh Space Camera will have a live broadcast of the event.

Regardless of how you experience it, you don’t want to miss this exciting event. Remember, no one alive today will witness it again!

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