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.”