JUPITER & GRS -- PC-33C - 25cm Newtonian @ f/24

The last several years have seen an upsurge of interest in video astronomy and video astrophotography.  This interest is due in part to the fairly recent availability of video systems designed specifically for astronomy such as the excellent line of Astrovid cameras offered by Adirondack Video Astronomy of New York and to a number of consumer video camcorders capable of imaging in very low light.  However, and perhaps arguably, the biggest reason more and more amateurs have been trying their hand at video astronomy and video capture astrophotography is because of a single camera introduced a number of years ago by Supercircuits of Liberty Hill, Texas, the PC-23C.

Being what is termed as a video surveillance camera head, the PC-23C is not unlike those video security cameras seen over the heads of bank tellers and convenience store cashiers.  The camera consists of a small, lightweight housing containing a sensitive, monochrome video CCD chip, a microphone, a small quantity of associated electronics and a threaded collar for attaching ‘C’ mount cine/video lenses.  There is no built in recorder or monitor so its video signal must be transmitted via coax cable to a video monitor and/or recorder.  What has most attracted amateur astronomers to this particular camera is its extreme sensitivity, 0.04 Lux and its unbelievable low price of $89.95! (at the time of this writing)

Early in 2002 Supercircuits released what is essentially an updated version of the venerable PC-23C, the PC164C.  Smaller and lighter, the new monochrome camera continues to utilize a 1/3 inch CCD video chip, but the new Sony Super HAD EX-view CCD is considerably more sensitive with a Lux rating of 0.0003 to the PC-23C’s 0.04.  What this means to the amateur astronomer is recording stars at least 2 magnitudes fainter than with the PC-23C.  The more sensitive camera will also allow larger image scale with smaller scopes when doing lunar and planetary astrophotography.  In addition, a number of deep sky objects can now be observed in real time with moderate to large aperture scopes.  This new camera has quickly been embraced my amateurs, particularly those doing planetary imaging, and, lunar and asteroid occultation timings.

VIDEO IMAGING WITH SURVEILLANCE CAMERAS

Attaching the PC-23C, 33C or 164C to any telescope is almost as simple as changing eyepieces.  With a 1¼-inch adapter that threads directly into the camera’s ‘C’ mount collar, the camera can be inserted into the telescope focusing drawtube, replacing the eyepiece.  With coaxed cable and 12 volt DC power connected, almost magically a live video image of lunar craters or planetary features appear on the monitor or portable television.  Utilizing a Barlow lens, magnification, or, image scale, can be increased to see finer details.   And, tweaking brightness and contrast on the video monitor will bring up dark features or reduce brightly-lit regions.  Essentially, any solar, lunar or planetary features you can see through and eyepiece will be presented on the monitor.

Now; with that said, it should be noted that recording much of what can be seen onto videotape is not quite as straightforward. 

Most video monitors or televisions can be adjusted through a very wide range of brightness and contrast allowing the observer to view craters, sunspots and planets at varying magnification, or image scale.  But, a typical video recorder cannot be adjusted in like fashion.  It requires that the video signal from the camera contain an image with brightness and contrast that falls within the narrow range the video recorder is capable of recording.  This brings us to the biggest single crux in utilizing video surveillance cameras for astronomy.

The vast majority of video surveillance cameras, including those from Supercircuits, do not have manual control of shutter speed or gain.  Instead they rely upon an auto exposure system that controls the shutter speed, gain, and the iris control on the cine/video lens typically used for surveillance.  Since a camera lens is not used when doing video with the telescope, the auto iris control will not be discussed.  However, the auto gain and auto shutter controls still must be worked with.

What happens when video imaging a planet is the camera’s auto exposure system sees the predominantly black sky around the planet and tries to compensate for the black by lowering shutter speed and increasing the gain.  As the camera gain increases, so too does the brightness of the planet disk to the point where it goes completely white.  To see and record surface features on the planet, the image scale must be increased so that the planet disk fills more of the video frame causing the auto gain to back off.

Image scale can be increased by placing a Barlow lens between camera and telescope, or by using eyepiece projection.  With eyepiece projection image scale can be adjust by using different power eyepieces and by varying the distance between the exit pupil of the eyepiece and the camera CCD.

With the moon or sun [appropriate (!!) solar filtration] the auto gain is less of an issue, in most instances, as the illuminated surface of the moon is not unlike the terrestrial views here at home.  However, when video imaging lunar features, which include shadow portions of the terminator or the black sky at the limb of the moon or sun, the image, will appear over exposed.  Adjusting the composition so there is less black sky or shadow region will generally bring the brightness down to recordable levels.

To be sure you are recording what you see on the video monitor, you must first determine whether what you see on the monitor in terms of brightness/contrast is what you need to obtain a good recording.  To initially calibrate the monitor, place a video tape in your system that has well exposed daylight landscape views, either ones you have recorded yourself with a commercial camcorder, or, use a commercially produced video movie (monochrome or color, it doesn't matter).  In a darken environment play the tape and adjust the monitor brightness and contrast to taste – this is the initial calibration.  Mark the dial settings on the monitor with a pencil or tape.

To refine the monitor calibration, set up the telescope, camera, recorder and monitor and focus on a planet, or a crater near the terminator.  Without touching the monitor settings, adjust the image scale until you see a well-exposed image, then record.  Now, go through the frame capture process with your computer and evaluate the quality of the digitized image on the computer monitor.  If the image appears too dark you need to reduce the brightness setting of your video monitor.  If the image is too light, then increase the brightness setting on the video monitor.  Mark new dial position and record again, then digitize a frame and again evaluate brightness on the computer monitor.  [the assumption is made that you have already gone through the appropriate steps to calibrate your computer monitor for the image processing software you are using]

With the video monitor now calibrated for best exposure, you have only to change image scale of planet, crater or sunspot to adjust brightness on the monitor, resulting in a recording with a good, recordable brightness range.

The PC-23C, PC-33C and PC-164C cameras have each proven to be outstanding for solar lunar and planetary imaging within the limits of their auto exposure systems.  The resolution of the 3 cameras is also respectable, between 420 and 480 horizontal lines.  Their 1/3-inch CCD chips make them well suited for high magnification imaging with faster telescopes.  In particular, the new PC-164C with its higher sensitivity is particularly capable with smaller aperture telescopes.  The accompanying astrophotos clearly demonstrate their capabilities.

I have not yet had the opportunity to work with the color version of the new PC-164C, but have no doubt it will be excellent for high magnification, high resolution color images of the planets.

By far the biggest shortcoming of these cameras is the lack of manual control of the shutter and gain, and no means of adjusting gamma.  Because of this they are not effective in producing wide field images of the planets or moon where a great deal of dark sky is included.  It is also difficult to create mosaic images of the solar or lunar surface, as moving to darker or lighter regions changes the video exposure causing captured frames to be difficult to blend into a smooth, continuous mosaic.

The auto gain can also be troublesome when recording lunar occultations that occur very near the bright cusp or illuminated limb.

The 1/3-inch chip is somewhat restrictive with longer focal length telescopes as a very narrow field of view results.

The PC-33C tends to record on the yellow side, but with appropriate color correction filtration this may be only a minor shortcoming.

The loss of the microphone in the new PC164C cameras.  The microphone was very useful for lunar occultation timing and would have been well effective for asteroid occultations with the new camera.

CONCLUSION

Over all I would rate all three of these cameras excellent, leaning towards outstanding in the case of the new PC-164C.  Each performed well right out of the box.  No matter how you look at it, each of these cameras is an excellent value to the amateur astronomer whether he or she wants it only for occasional public programs or to seriously pursue video capture astrophotography.  The PC-164C is particularly well suited for high resolution imaging of the planets and lunar surface.

Can these cameras take the place of fully manual video systems like the Astrovid 2000 or the recently introduced video frame integrating Astrovid StellaCam cameras?  Not entirely, the surveillance cameras do not have the resolution of the manual controlled cameras which utilize 1/2 inch CCD video chips.  The manual controlled cameras allow a greater freedom to record at any image scale which is difficult or impossible with the surveillance cameras.  Also, the larger video chip in the astronomical cameras allow a wider field of view.  And, of course, none of the these cameras are suitable for deep sky viewing and imaging.  Still, when one considers what the surveillance cameras are capable of doing, and at a fraction of the cost of specialized astronomical cameras, the amazing value of these cameras becomes quite apparent.

Along with the PC-line of cameras, Supercircuits also offers a number of items of particular interest to the amateur astronomer.

Monitors – they offer a number of monochrome and color monitors, but of particular interest are the 12VDC portables.  Their 6 inch monitor designed for use in a vehicle has duel video input and a built in camera switching circuit that allows the monitor to go back and forth between two video inputs.  This would be great for public programs where a telescope has two cameras – one on the main scope and one on a smaller guide scope or finder.  The monitor would automatically switch back and forth between a close up view of the moon and a wide field view.

Time/Date Generators – they carry a small 12VDC model that would be well suited for field use.  With it you can record right on the video image date and time in hours, minutes and seconds.  They also offer a 115VAC version.

Video Capture Devices – the SVG-1 video digitizer with USB interface allows the recording of video directly to the computer, or, the capturing individual video frames.

Video Amplifiers – for those working with remote telescopes, these amplifiers allow cameras to efficiently operate several hundred feet away from the monitor/recorder.

2.4 GHz Wireless transmitter/receiver – for operating the telescope without coaxial cable between the camera and monitor/recorder.  Along with remote telescope operation, these units would be great for public programs as they eliminate the trip hazard of having coaxed cable hanging between camera/telescope and monitor.

PC-102C – for those interested in fabricating their own camera, Supercircuits offers a number of circuit board cameras.  Of particular interest is the PC-102C, which is a high resolution, 570 horizontal lines, camera with manual gain and gamma, and a 0.05 Lux rating.  With moderate to large aperture telescopes this should be a killer camera.

PC-152C – finally, for those on a really tight budget.  Similar in size and shape to the PC-23C, this 0.5 Lux, 380 line resolution, monochrome camera, also with auto gain and shutter sells for far less than an eyepiece at a mere $49.95 (at the time of this writing).
 

Check back as more will be added soon!

1 April 2002  Jim Ferreira  bakerst@comcast.net     http://www.lafterhall.com/astro.html