Webcam Autoguider

My most recent project in the pursuit of better pictures was a webcam autoguider. I was very satisfied with the selfguiding of my Starlight XPress MX512 camera with the STAR2000 interface, but wanted to avoid the halved sensitivity due to the selfguiding.

My research for webcams on the net gave the result that the black and white Quickcam was best fitted to astronomical use because of it's good sensitivity and the availability of modified drivers that allow for long exposure times. Unfortunaltely this camera is out of production for quite some time, so I had to resort to another model and from what I read the Philips Vesta Pro was the best current model. I bought the Vesta Pro and also the newer model Philips ToUcam Pro. Testing in a dark room with LED's of different colours gave me the impression that the newer model was a bit more sensitive and it also seemed to give sharper pictures (even when swapping it's lens with that of the Vesta Pro), so I decided to return the Vesta Pro and kept the ToUcam Pro. Both models are supposed to have a chip by Sony, which I liked as Sony chips usually have low dark current, which would be important for an uncooled camera. The chip has 640 x 480 pixels on a small (even smaller than in my MX512) chip at a size of 6,4 microns per pixel.

The modification for astronomical use was easy, I just unscrewed the supplied lens (which doesn't require any tools nor opening the housing) and glued a storage box of a Fuji colour film on the housing (after cutting of the bottom part of the box). Some (not all) of these film boxes fit a standard 1 ¼ inch eyepiece holder nicely.

I also opened the housing to put a tape over an LED that shows when the camera is recording videos because this LED shed it's light into the housing as well as outside. This didn't give a noticable performance boost though, so one might get along without covering the LED.


The webcam connects to the USB port of my notebook and operates nicely within AstroArt ( ). On the AstroArt webpage a driver for webcams can be downloaded, with this driver the webcam can be treated just like a normal CCD camera. AstroArt even allows for long exposures by automatically adding or averaging multiple exposures (which of course is not as good as true long exposures). I usually set each guiding exposure at 1 second. As the ToUcam Pro allows for 5 frames/second as longest exposures, this one second exposure should be the average of five frames, which gives a noticably better limiting magnitude than the live video stream.

The readme-file for the webcam driver explains how to use two cameras (CCD and webcam) simultaneously on one computer, one just has to copy a *.dll file into the AstroArt directory after renaming it (so one ends up with two times the same dll but under two different names). Now I can run my MX512 camera from the parallel port and the webcam from the USB port of my laptop. I found out that one has to start two instances of AstroArt though as the continous reading of the webcam blocks everything else in that instance. No problem, just start AstroArt a second time and use the second version to control the CCD camera (or vice versa). For connecting the notebook to my LX200 I use the cables (including STAR2000 box) I have previously used when selfguiding with my MX512. Of course the STAR2000 box is not necessary when guiding with the webcam, any cable from the serial port of the notebook to the RS232 or autoguider port of the LX200 should work as long as it is suitable for controlling the scope with the notebook.

As the webcam is not very sensitive compared to my MX512 camera, I found it necessary to couple it to a freely movable guidescope. With the ability to easily move the guidescope it usually is possible to find a bright enough guide star even under my light polluted inner city skies. Under a dark sky a suitable star should be almost anywhere the scope points to unless it points to an area where very few stars are. Although I haven't done any quantative measurements of the webcam's sensitivity I usually find that it can guide on every star that is clearly visible in my 8x50 finderscope when coupled to my 90/500mm Maksutov guidescope. The Maksutov is equipped with a standard camera tripod adapter, so I simply put it on the piggyback bracket of my LX200. I didn't have any problems with the stability of this setup and it allows for simple horizontal movement. The focal length of the guidescope is not critical, one of the usual 80/400 mm shorttube scopes should be enough for modest focal lengths of the main scope as AstroArt gives subpixel accuracy during guiding.

The results of this setup have been quite encouraging, if I can find a bright enough guide star the webcam guides almost as good as my MX512 camera. I just have to fine-tune the guiding parameters a bit more to get to the same accuracy.

Click below for some pictures that were taken with this setup.

M27 for 7x10 minutes NGC 7331 for 11x10 minutes NGC 7217 for 9x10 minutes Pk 112-10.1 for 15x10 minutes

Update: After some initial success I have given up on webcam autoguiding as there were too many objects where I couldn't find a suitable (=bright) guidestar. I have since used a Mintron video camera that has the same CCD chip as my old Starlight Xpress MX512 camera and allows for exposures up to 2.56 seconds. This camera is sensitive enough to find a guidestar almost everywhere I point the scope, I don't even have to move the guidescope (a cheap 70/700mm refractor).