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- Review of Explore Scientific First Light 8
- Rebuilding my CGE Pro
CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.
Getting Started in Astrophotography using a Webcam
Astrophotography is a very difficult subject in the past, but it has becoming easy. In this article, we introduce one of the easiest and cheapest ways to take images of the night sky.
Webcam is a small digital video camera used for video conferencing. They have been designed without astronomy in mind, but they work surprisingly well for taking images of brighter celestial objects like the moon and the planets.
Webcams are cheap, and widely available. No film is required for taking pictures. Results can be seen instantly, and they are in digital format, which can be processed very easily. And the most important, it is very easy and it can produce very high quality images! Therefore, it is a very good starting point for any people who wants to get their hands wet with some forms of astrophotography.
Here is a list of equipment required:
- Any telescope which can exchange eyepiece (!)
- A good quality webcam, usually with CCD instead of CMOS, with hardware resolution of 640x480 or better
- A tracking mount, either altazimuth or equatorial, but it is not a must
- Suitable barlow lens to get larger images, but again, it is not a must
- A desktop PC or better yet, a notebook PC which you can carry round more easily
As you can see, nearly any telescope will do the job and I have some examples taken with a 70mm telescope shown in the last section. I have captured the Great Red Spot on the Jupiter and the Cassini division on the ring of Saturn with a 70mm telescope on a fixed camera tripod without tracking. So, you probably get better equipments than that already.
A very good webcam for this purpose will cost under $100 USD shipped to most place on the Earth, some good models are the Philips ToUCam, the QuickCam Pro.
A barlow is important to yield larger image scale for planets imaging, you will want your telescope to operate from f/20 to f/30 or even more for webcam imaging. A cheap model will be fine as the CCD chip is very small inside a webcam, and the on-axis performance of cheaper barlow lens will not be too bad usually.
A desktop PC is enough. I took images inside my home which is located at the urban center of Hong Kong. Light pollution is not important for imaging the moon and the planets. A notebook PC would be nicer in terms of portability, if the view from your home is obstructed by other buildings.
The exposure time of a typical webcam is limited to 1/25s, that means it can only be used for taking brighter objects, namely the moon and the planets, and the sun with proper filter.
For imaging with longer exposure time, the world wide web contains a lot of information on how to modify the electronic circuit of a webcam. With those modifications, you can take images of those dimmer objects. However, CCD has a drawback that noise will accumulate during longer exposure. The amount of noise is related to the temperature of the CCD chip, the higher the temperature, the more noise you will get. Thus, you will also want to cool the webcam to reduce the noise for longer exposure and it further complicates the matter. Also, the small size of the CCD chip inside webcam makes them less desirable for taking images of extended objects. Therefore, beginners are not advised to attempt longer exposure using webcams.
Connecting to the Telescope
Nearly all webcam has a threaded lens, you can screw it in and out to adjust the focus position for daily use. You will need to unscrew it totally since that lens is so small and unsuitable for astrophotography. The small lens will be replaced by your telescope, i.e. your telescope will become the lens of your webcam.
The above picture shows a typical webcam with an adapter for connecting the webcam to a telescope. The adapter can be bought from Mr. Steven Mogg or you can make it yourself by using a film canister. Just cut the end with a small cutter and then attach one end to the webcam by using glue or something alike. Because the diameter of a film canister is roughly 1.25", it fits nicely into the focuser of your telescope.
The adapter is just an empty tube without any optical element, so it would not be too hard to make one. I bought one off the shelf to get better optical alignment with the trouble.
The above picture shows the webcam with its lens removed. Notice that if you buy an adapter from Mr. Steven Mogg for your particular webcam, it will have thread which matches with the lens thread of your webcam nicely. On the other end of the adapter, standard filter thread is available as well.
You can also see the CCD chip inside the webcam. Try not to let dust fall onto it. If you see dust on it, just blow it away with a Hurricane bulb. An optical window is usually available to protect the CCD.
The above picture shows the webcam with its adapter on, you can simply plug it into your telescope like what you do with an eyepiece. A barlows can be added to yield larger image scale.
Capturing the Images
Ok, things were basically ready, and we can start taking pictures. Normally, I will go like this:
- Boot up the PC, with the webcam plugged in (it takes time!!)
- Setup telescope (a very fast step for me)
- Collimate your scope!!!
- Aim your target with an eyepiece, center it, use the barlow if needed
- Launch your webcam video recording software, fix the settings
- Remove the eyepiece, plug in the webcam
- Focus using your webcam, by looking at the display of your PC
- Center your target again with the webcam
- Sit back and refine the focus during moments of better seeing
- Capture when seeing is good
Some points to notice:
- Do not under expose or over expose your images, trivial? em...
- Use a gain value as low as you didn't under expose your image, it will give less noise
- Slower frame rate will give less noise, 10 fps is good enough, it will also avoid dropped frame for slower PC
- The planets rotate so that features will shift during the time you capture your video. To avoid problem for stacking, a video
- clip should not be too long, for around 4000mm, 100s is around the maximum duration. Such a limit would also be nice for altazimuth tracking which will result in field rotation, yet another source of problem for stacking.
- Don't capture too much video, it burns up your storage space and it burns up your time later when you have to process them, haha...
The picture above shows my bigger setup, which is a 8" SCT on an alt-az tracking mount. This picture is taken during a real imaging session inside my home, which is an apartment inside a heavily light polluted city. You can see that my window is pretty small, and it is barely enough to use a 8" SCT.
When the webcam is plug into your telescope, you can start taking images using it in the same way you use it normally for video conferencing or video recording. Please see the picture below to see what I usually see in the display of my desktop PC. It is just the software that comes with my webcam.
I usually set the webcam to capture 20 frames per second (fps) when I was focusing, and I will switch it to 10 fps when capturing the video for it can reduce the noise level.
Since the CCD chip on the webcam is very very small, it therefore, effectively a very high power eyepiece with a very very small field. So, you will want to center your target first before plugging your webcam in, or else you will have a hard time to point your telescope with a webcam. Dual axis motor drives will be useful since the CCD chip is so small that you will have to guide it during image capturing. So, my dual axis controller is usually placed at my side like below:
You can also see two eyepieces in the background, the 2" 40mm eyepiece is used for searching the target and the small orthoscopic is used for centering the target.
If you are using a tracking mount, you can proceed to take images immediately. However, if you're using a non-tracking mount, be sure to put your target object in a position with the consideration about that it will move by quite a bit during the time you plugg your webcam into your telescope. It is not terribly difficult with some practice. You can take images during the time when your target drifts across the CCD chip.
Wait for moments with better seeing, patience is important here. Since the webcam captures images fast enough, for most night, you will find moments with better seeing enough to produce very well images.
It is a good habbit to use the detail about your shot as the file name for record. For example, I will use the name sat-c8-3x-20030223-2200.jpg as the file name for the video clip captured at 22:00 in 2003-Feb-23 with a C8 using a 3x barlow lens and the target was Saturn. Invent your own naming convention.
Processing the Images
Image processing will not turn dead images alive, but it is one of the best way to bring out subtle detail on your raw images. Usually, we will stack the frames from a video, and then we will process the stacked image further to get the most out of it.
Raw image appears on the computer screen will not be very attractive, as you can see the Jupiter in the previous section on my display. Even the exposure for planets are short, there are considerable amount of noise as you can see.
Some raws are better than the others even in the same video clip. Some raws are better at one part and some raws are better at the other part of your target, so we can process them, to get the most out of them.
You can see some raw images below:
Stacking is a way to reduce the noise. Noise are random unwanted signals in our raw images. By combining the raw images, the signal to noise ratio increases, and we can therefore, obtain a cleaner image for further processing.
Each of them are different, and you can try to see which one suits you most. They have tutorial on their website and I am not going to repeat it here.
You can see a stacked image below, notice that it's far more cleaner in terms of noise than any raw frames:
Unsharp masking, color balance, brightness, contrast, etc...:
Some of the above stacking software includes the functionalities for unsharp masking. It is also available in Photoshop and many image processing software, and they are usually more powerful and flexible. Registax supports wavelet processing which worths some exploration as well.
Avoid excessive unsharp masking, for it will bring out noise. What is "excessive" is a matter of personal taste. Apply some Gaussian Blur can somehow fix excessive unsharp masking. "Despeckle" and "Remove Moire" can be used to remove some noise as well.
Color balance is required in some cases. Due to different atmospheric condition, your image maybe color shifted. For example, air pollution in Hong Kong from nearby cities will usually make images become yellowish, you can do some color balance to make the final image looks better. Also, don't rely on the auto white balance or color balance of your webcam, for it won't work well under the condition for planets imaging.
You can see a final processed stacked image:
Some final words
This is a starter guide only and we strongly recommend you to go further, and the most important, to practise more.
If you think you love to go with other forms of astrophotography, here is a few keywords you can start looking at: prime focus, eyepiece projection, single lens reflex, guide scope, off axis guider, cooled CCD, etc.
The following examples are not those show case pictures, and actually, many people can produce far more pleasing photographs using similar setup. The examples here serve as a demonstration to show what a beginner can do within their first few nights of webcam imaging. If you try to carefully collimate your telescope (easy and must try), wait for moments with better seeing, get a good focus, and you are done!
Please see below some examples captured by a 70mm refractor:
Please see below some examples captured by a 8" SCT:
You can probably attain similar standard after a few trials, depending on your patience and the sky condition you met. Good luck and enjoy!
- Tenacious and seckroaad like this