Composing faint or invisible deep sky astrophotography targets can be problematic. Fortunately, there are tools and techniques that can help with composing your target.
There are two good and free tools you can use during planning to compose your image and determine the correct focal length to shoot the target.
Stellarium is a free app for Windows and Mac that will not only visualize the location of the objects in the night sky, it will also show you how your object is framed with your camera and lens combination. This feature is only available in the desktop PC versions not in the iOS or Android apps.
Stellarium is easy to use. Here are the steps to set up and use the framing feature in Stellarium.
- Click on the Oculars Configuration Window (wrench icon in the upper right)
- Click on the sensors tab. If your camera is not in the list, you will need to set it up.
- To set up your camera, you will need to know the sensor size in millimeters, resolution, and pixel height and width . If you don’t have it memorized, you can look it up in the Digital Camera Database. The pixel pitch in the Digital Camera Database is the closest thing I can find to pixel height and width.
- On the telescope tab, you can add your lens if it is not already in the list. You will need the focal length you will be using and the diameter which can be found doing an internet search.
- Moving your cursor to the lower left side of the screen, you can bring up the date/time window. Enter a date and time that your object will be in the night sky.
- Also in the left menu, click on the search icon (magnifying glass with a star in it) and enter the object using the catalog name (M42, NGC 2024, etc.)
- In the upper right menu, select the Image Sensor Frame icon (2nd from the left). This will bring up a rectangle showing the field of view for the camera and telescope/lens combination. Click on the arrows for sensor and telescope to select your camera and lens.
This will give you a good idea on how the Deep Sky Object (DSO) will be sized and positioned in your frame.
Another tool for planning your composition, is a website called Telescopius. Telescopius provides a similar framing feature as Stellarium.
- Simply enter your DSO by the catalog name in the search at the top
- Scroll down to the telescope simulator
- Click on the Lens icon and enter the focal length
- Click on the Camera icon and enter the sensor size
You should see the how the DSO is framed with your camera lens combination.
Telescopius is quick and easy to use. However, you can set up and keep all your cameras and lenses in Stellarium. Stellarium also has a bunch of other features to plan your astrophotography shoot.
Written by Martin Belan
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