Telescope Reviews: Analog Video Technology (Part 1)

Part 7a

I'd like to discuss converting analog video into digital format for storage/record-keeping, post-processing, or printing purposes.
This is commonly known as video capturing.

First, few caveats:
- There are many video capture cards/devices with various designs/quality/models-versions
- even with the same vendor and same model number, the chipset may change, the included internal memory size may change, and the software driver may change
- software driver may not work correctly and/or may crash your PC occasionally
- when low compression rate, high spatial resolution, and high frame rate options are chosen, it adds a lot of load on the bus where data is transferred, on the CPU, on the
memory consumption, and on the harddisk access rate/usage

Still feel compelled, then check vendor's return policy and start experiment

================================================================

For a color video camera running in long exposure mode (e.g., 1 second exposure), IMO, there really isn't worthwhile to perform full video capture. Note that In one second interval, NTSC video has approx. 60 fields or 30 frames while a 1-sec long-exposure video has:
- one useful-new information frame and 29 identical (redundant) frames, or
- one useful-new information field and 59 identical (redundant) field*

* In long exposure mode color video camera, a field-integration mode on interline-interlaced CCD is used. After that read-out, the next field no longer has information from CCD to use, so it has to replay the previous field's information, and so do the next 58 fields, i.e., 29 * {odd field + even field}.
The visual proof is in one of the Astro Video Image Gallery picture where a plane flew by causing a slanted line. Using pixel peeping (and discount the JPEG artifacts), the line showed double-line structure, and when jumping to the next line grid, it's always in a 2-line unit fashion.

It is quite ironic. In early days, built-in compression (even a partial function) capture devices are highly desirable, can have a very high price tag, and were very hard to find.
In recent days, for astro video capture application, low or minimum compression capture devices are highly desirable, can have a high price tag (due to supply and demand), and the reliable ones are very hard to find.

Next section I will try to explain the format and interface methods.

Clear Skies!

ccs_hello