Bright or at least relatively bright comets like 46P/Wirtanen don’t come by very often. When they do, we want to try and capture a photo to share and remember the sight. I’ve seen dozens of photos of the comet in the past few weeks taken with everything from mobile phones to expensive telescopes. Not surprisingly, I’ve been out snapping away every clear night. And with the recent cornucopia of clear skies over the region, I’ve been busy!
After taking pictures at night for some time, it becomes second nature to set up quickly and have that first image taken within 5 minutes. Here’s my usual procedure:
- Attach the SLR camera to a tripod and turn the shutter speed knob to “M” for manual. Then turn another knob or dial, usually located near the shutter button, to select the length of the time exposure. Most digital SLRs and even some point-and-shoots can expose up to 30-seconds.
- Use a standard 35mm lens and point the camera at bright star then click the “live view” button. This turns the back screen of the camera into a live view of the scene. With the lens set to manual, focus manually on the bright star until it’s a sharp pinpoint.
- Next, compose a scene with constellations or the beautiful Pleiades and Hyades clusters the comet is currently near.
- Open the aperture to its maximum (f/2.8), set the light sensitivity to ISO 800 and shoot a 20-30 second time exposure. Depending on your lens, its maximum opening might be f/3.5, f/4 of f/4.5. Go as wide as you can.
Now, just click away, checking the back screen to make sure your exposure’s on target. If the image is too dim, increase the time or dial up the ISO to 1600 or even 3200. If you use a telephoto lens to photograph the comet, you’ll have to keep exposures short so the stars and comet don’t trail because of Earth’s rotation. With a 200mm lens I can only get away with 2-3 seconds, which means I’ve really got to crank up the ISO. Wide-angle lenses are more forgiving and don’t show significant star-trailing up to 30 seconds. If you don’t want any trails then you’ll need to invest in a special tracking mount.
I use the iOptron SkyGuider Pro EQ camera mount. Others like the Vixen Polarie. You screw the mount onto a tripod and manually align it to the North Star. Sometimes it takes a few minutes for a good alignment but once set, you can shoot longer time exposures at lower ISO speeds for great quality images with pinpoint stars. I typically expose for a minute or two at either f/2.8 or f/4. You can go longer, but after a few minutes, sky glow will overexpose your images.
Lots of astrophotographers now take multiple short exposures of the identical scene and then “stack” those photos into a single, high-quality image using stacking software. I’m just starting to do this myself. If you’d like to try it, check out this site for several good software options. One not mentioned there that’s very popular with amateur astrophotographers is the free RegiStax program. Stacking makes for high-quality, nearly grain-free photos that reveal more details and more stars in your photos.
The moon is starting to get bright, but I encourage you to keep following the comet and maybe even try your hand at photography. The next couple nights will still be good ones, and then you can start up again around Dec. 24 after full moon.