The modest web camera (or webcam) quickly gained interest among amateur astronomers and is now considered as the equipment of choice for planetary imaging because it has two characteristics that are very much useful in astrophotography: (1) its lens can be removed much like the lens of a DSLR, making it possible to easily connect the webcam with any telescope and (2) it can record a huge number of still frames even in a short span of time (1-2 minutes), a feature particularly useful in a post-processing technique called registering and stacking. In this article, I intend to describe how to image planets using a web camera as the main imaging device and then provide a brief overview of the post-processing technique.
Any web camera may be used for astrophotography, some cameras however, perform better than others. Two of the most popular models are the Logitech Pro 4000 and the Philips SPC900NC, both of which are equipped with CCD sensors that produce far better images than other cameras of the same class, equipped with the lesser sensitive CMOS sensors.
Images may be captured using 2 different imaging techniques: (1) prime focus method and (2) eyepiece projection method. Details about each method and the accessories needed are described below.
The prime focus method involves replacing the web camera’s lens with the lens (or mirror) of a telescope. The idea is to focus an image of the target (in this case, a planet) directly onto the web camera’s sensor. It requires a web camera (with the lens removed), a camera-to-telescope adapter, and a telescope.
In planetary imaging, it is important that the telescope has enough magnification to be able to capture considerable amount of detail. I recommend imaging at a focal length not less than 1000 mm. If your telescope is a bit too short, Barlow lenses may be inserted along the optical path to achieve longer focal lengths. Limit the number of Barlows to at most 2 to avoid image degradation, and as a general rule, always minimize the number of Barlows used — use one 4X Barlow lens instead of using two 2X Barlows stacked together.
The eyepiece projection method involves projecting an image onto the web camera’s sensor with the help of an eyepiece. This is a more complicated technique as it requires more adapters, but it is all worth it since it tends to produce higher-quality images than those achieved with a prime focus setup. It is advised however, that you should learn prime focus imaging first before attempting eyepiece projection method. It requires a web camera (with the lens removed), a camera-to-telescope adapter, an eyepiece projection adapter, an eyepiece, and a telescope.
Using a higher-power eyepiece produces a larger image (higher magnification). Also, increasing the separation between the eyepiece and the sensor further increases the magnification. If higher magnification is desired, one may simply replace the eyepiece with a higher-power one, or increase the separation instead by using a tube extender. Barlows may serve as tube extenders provided that the ‘lens’ is removed.
In planetary imaging, our goal is to record 2-3 minute videos of the planet we wish to image and then use a software to extract still image frames from this video (remember videos are just still images displayed in sequence), scroll through the frames and look for the best-looking image (sharp, clear, with lots of details), and then use the software to look for other images that are similar in quality. These frames will be aligned automatically and then combined to form one single image. Comparing all other frames one at a time with the best-looking image is called registering, while the process of putting all those similar frames on top of the other, aligning them automatically, and then combining all of them to form one single image is called stacking.
There are several freeware that can perform registering and stacking, one of which is called RegiStax. By registering and stacking images, sharp details are preserved, noise is greatly reduced, and the resulting image looks clean and smooth. The software may be downloaded here. I strongly suggest that you try to learn how to post-process recorded clips, I guarantee you will be amazed with the results! It is not really as hard as it sounds.
I hope this article provides ample information to help you get started in planetary imaging! Should you have any questions, feel free to leave a comment. Clear skies!
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© Anthony Urbano (Manila, Philippines)