Since 1988 I have been experimenting with various types of analogue video cameras to obtain images through the telescope, and to subsequently digitise the tape images with a suitable capture device in a computer to produce hard copies. In those early years suitable computer hardware was not readily available, and the cost was prohibitive. With cheap digitisers, image grabbing was rather disappointing. Some success was achieved with a 1.5 A Hydrogen-Alpha filter for solar prominences, and white light solar disc videography with an aluminised solar filter which I made in 1966. Various domestic video cameras were used on a 4" f/10 Criterion SCT, with less than optimal results. Prominence photography has problems all of it's own!
Increased solar activity has once again stimulated my interest in this form of astrophotography, and I would like to share my experiences in electronic imaging.
The photographs produced here demonstrate what can be achieved with readily available domestic equipment and a small telescope. The images presented were taken with a home built 82mm F/15 achromatic refractor and a Takahashi FS 102 F/8 Apochromatic refractor. Two types of video camera's were used, a Panasonic 350 Colour ½"CCD 410 line surveillance type camera almost 10 years old, and a recently purchased USA manufactured ASTROVID 2000 black & white ½" CCD 600 line camera, specifically made for high-resolution astrophotography. Video images taken with a colour video camera are noticeably grainier than a black and white camera, which makes a colour camera less suitable. However, the solar prominence pictures look more realistic in colour, and with plenty of light available, it is worth taking pictures with both cameras. Equipment Setup
One of the problems that confront most astrophotographers is the variability of the seeing conditions, and even with good transparency and clear skies, the atmosphere may be very turbulent, mostly the case with solar work. As a keen astrophotographer since the mid 1960's, I would not like to think about the vast amount of film that I have wasted to get a few useable photographs of the sun, moon and planets. Videotape is comparatively cheap, even top quality professional grade tape.
Here are some interesting figures. In one-second of interlaced video there are 25 frames (pictures) and each frame consists of two fields (pictures) which are interlaced to form a single frame, so every second there are 50 pictures taken at 1/50th second. The down side of this two field interleaving is that if the object is moving during the two scan passes, then the resulting still frame is not sharp. This can be overcome by accessing each separate field. There are new cameras on the market which have Progressive Scan CCD chips. These rather more expensive CCD's capture a single frame of 1/25th of a second duration to overcome the movement problem. This gives a slight stroboscopic effect to normal video and is primarily used for still frame capture applications. Most video cameras are also equipped with a variable speed shutter, which helps to reduce movement at the expense of less exposure.
There are two very appealing facets to using videotape for astrophotography, one is the very short field or frame exposure time of 1/25th - 1/50th second and the other is the large number of pictures that can be captured on a standard three-hour videotape. The thinking here is that it should be possible to obtain a sharp image or two during each second, and subsequently extract them at the editing stage. In ten seconds worth of videotape there are 500 individual pictures, so there are 540,000 pictures on a three-hour tape costing perhaps $20. Compare this to the cost of 15,000 rolls of 35-mm film plus processing, and suddenly a roll of videotape looks a very attractive option!
With a video camera attached to the eyepiece focuser of the telescope the image is displayed on a TV monitor, and the large on screen image looks very impressive. Many observers can view this at the same time, which is a useful feature at an open night especially when it is cold and the object of interest is gradually disappearing from view. The other appealing feature of video astronomy is that with videotape one has instant recording and playback, either as video or for later digitising the still images. Hard copy images are great for record keeping, publication or transfer via the Internet to other observers. There is no waiting for films to be processed only to find that the exposures were wrong or the slide film got lost in the mail! This approach to imaging through a telescope opens up an interesting move into the non-film era.
With an appropriate computer video capture card, I am able record the image either direct into the computer and / or onto videotape. This allows me to produce a still image, which I can then print out on a photo quality colour printer, without even leaving the observatory. This technology does allow me to obtain pictures that would be difficult to obtain by more traditional methods. This technology will be covered in Part 2.
However, all is not as simple as it first appears. There is the cost of the equipment to consider, and to access the individual video fields at 1/50th of a second does require expensive professional equipment. Assuming that one has access to normal domestic video recording equipment with good still frame capability, then 1/25th of a second pictures are readily available. Another drawback with videotape of course is the electronic noise that gives a still frame that grainy appearance. This signal to noise ratio is worse in poorly lit situations. This can be overcome to some extent by using a black and white camera, and at a later stage when the image is manipulated in the computer. This aspect will also be covered in Part 2.
The type of video camera used is quite important, it is preferable to be able to attach it directly to the telescope without any other lenses, and to be able to manually alter the exposure controls such as the shutter speed, gain, and contrast. This is readily achieved with the purpose built ASTROVID 2000 with it's external control box. Whilst looking at the TV monitor, the brightness, contrast and shutter speed can adjusted to suit the object without touching the camera and causing unwanted vibrations at the telescope. With other types of cameras, the controls are part of the camera, so movement is introduced to the telescope whilst making adjustments, an undesirable effect. In general most surveillance type video cameras and domestic cameras have either tiny control switches or on board menu adjustments. These are often difficult to use in the dark with cold fingers.
The video cameras used can be fitted with a fast video lens of F/0.9 or F/1.2 or fitted with "C" mount to 1¼" eyepiece adapter for use on the telescope. A "C" mount to 35mm camera lens mount to suit my Nikon and Pentax 35mm SLR cameras can be used with fast 35mm lenses for telephoto effects. Interesting star fields are easy to capture on video, using a Nikon ED F/2.8 80 - 200mm zoom lens. Surveillance type video cameras with "C" mount fitting are very versatile. Keep in mind that even a standard 50mm camera lens is a telephoto lens when used on a CCD video camera. Of interest is the new Sony Exwave HAD ½" Colour Camera, this has excellent low light sensitivity with accurate colour reproduction, and is a significant improvement over the older model Panasonic 350 described above.
The use of video cameras for astronomical imaging can start at any level, with quite satisfying results. I am fortunate that I can combine my professional expertise and equipment with my hobby.

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UPDATE - January 2000

Since this article appeared on the ASTROVIDEO Website, I have had many requests for more information on the type/make of S-VHS VCR I use, and the Frame/Field selection. I have several top end domestic S-VHS VCR's with normal Jog/Shuttle control and even serial interface for control by computer, however, these machines do not have access to single video fields. With standard domestic VCR's there is no requirement for such access, and it adds considerably to the cost.

The S-VHS VCR I refer to and use is a Panasonic Model AG-7355. This is a professional industrial VCR, with Digital Frame Store, Stereo VU recording level meters, and many features not found on domestic recorders. The cost of such a VCR in Australian dollars is in the region of $6,575. In general, if your VCR does not have a switch to swap between frames or fields, then you can be pretty sure that this feature is not available.

This particular Panasonic model is equipped with a precision jog/shuttle and digital frame store for rock solid still frames. It also has a special facility to access a single video frame, which consists of 2 fields, with access to either field 1 or field 2. via a little switch located under a panel on the front of the machine.

I also have a Sony Video Printer UP 2200 which allows access to either a frame or fields 1 & 2. I still have an old Amiga 2000 computer with a Time/Base corrector card which allows capture and display of individual fields, and it clearly demonstrates the movement (jitter) between the two fields if the subject is moving during recording.

I have recently purchased an Integral Technologies Capture Card - FlashBus MV Lite, through Adirondack, and this card is able to capture either frames or fields. I am putting together a dedicated Pentium computer for this card and related astro CCD cameras / software, so have not tried it out yet.

My direct video capture to hard disk and capture off tape has been done using a Miro DC 30 Plus Capture Card. This works very well and has a very useful Video Capture device that allows control over the brightness, hue, contrast of the incoming video, and batch capture to a 'Project' file. However, I use this system for video editing and BMP still frame capture and is not really set up for use with the telescopes. I will update this article with some still frame pictures as time permits.

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Equipment Setup

Southern Cross Observatory

Solar Image Page (New)

Lunar Image Page (New)

Deep Sky Image Page  (New)

Transit of Mercury 1999  (updated 2/2000)

ASTROVIDEO Website

Astrovid 2000

Eddie Trimarchi (Australian Amateur)

Tasmanian Amateur Astronomers online

Astronomical Society of Tasmania