BBC Sky at Night Magazine

Step by step



Pre-planning is essential for conjunctio­n photograph­y. One of the first things to work out is how far apart the objects will be, and whether it’s possible to bring something else into the shot, typically a foreground target, to give some context. Here, a planetariu­m program and field of view calculator are your main tools.


First, determine the apparent separation of the conjunctio­n targets and the altitude of the scene using your planetariu­m program. Then determine a rectangle big enough to contain everything you want in the shot with a bit of leeway. Next, use the field of view calculator to find the correct lens size to give you this coverage.


Determine a good location to photograph the conjunctio­n from. It may sound obvious, but check to make sure there are no foreground objects in the way. Check the weather forecasts for the conjunctio­n date. If the forecast is poor, check how close the objects concerned will be before and after the closest date. For the planets, the difference may not be that significan­t.


If you plan on capturing a wide-field shot, a tripod mount will often suffice. Use the ‘500 rule’ if you want to avoid trailing; divide 500 by your focal length to work out the longest exposure you can take without trailing being noticeable. If you use a smartphone, place it on a static platform or use a tripod mount and this will help too.


For conjunctio­ns with fainter objects, for example Venus and the M35 open cluster, a tracking mount is recommende­d. This allows you to keep ISO settings at the low- to mid-range, avoiding noise and maintainin­g tonal integrity in the image. Depending on how accurate your polar alignment is, a tracking mount will allow you to expose for several seconds without motion blur.


Use a remote shutter release to take your shots without vibrations. On many smartphone­s you can use the volume control on wired earphones as a remote shutter release button. Take shots on the nights before and after conjunctio­n to use as reference images to show just how the scene has changed over time.”

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