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Video Astrophotography

All information and pictures supplied by video astrophotographer Greg Roberts, Cape Town.
More on satellite tracking and video astrophotography can be found on Willie Koorts' homepage

Information Guide: The Use of Videography in Tracking Earth Satellites
By Greg Roberts

An informative "how-to" guide in satellite tracking:

Download: 1.83 megabytes PDF file

Original source of document: Space Surveillance

Satellite Tracker

Left: Greg Robert's 6 inch reflector mounted in an alt-azimuth configuration. Very little vibration is felt. This telescope is used in the video capture of satellites and for tracking purposes.

Image at right: diagram of the ASTRA satellites.
Credit: SES Astra.

ASTRA group of satellites and GUIDE area

Photo credit and information: Greg Roberts. 13 February 2007

To the left (top) is a picture of the ASTRA group of satellites as seen with a 6 inch f/5 reflector. The white image at bottom left shows the area of the sky where the satellites are, according to the GUIDE application.

It is not possible to identify with 100% certainty which
Astra satellite is which, as the grouping is so close that radar tracking cannot isolate each individually.

The field of view is 28.2 x 22.5 arc minutes and centre of
field is about RA 06h02m30s, Dec +05deg27'11" (J2000).
The faintest star identified is in the vicinity of magnitude 14. Note the telescope was kept stationary, making the satellites appear as dots, whilst the stars are trailing in the background.

During the period of 24 hours these ASTRA satellites perform
quite spectacular "lissajous" figures as they move about their
mean position (due to them having different orbital
inclinations). With enough time and effort it will be possible to make a time-lapse movie of this group.

The camera was a MINTRON -12V1-EX operating with an
exposure of 2.56 seconds. No image processing was done
other than to remove the more obvious dead/hot pixels.

Click for larger images.

Experiments with video: M42 and the Pleiades

Photo credit and information: Greg Roberts. These images show what happens when the focal length is not matched to the pixel size - (i.e. one needs a longer focal length). Camera used was a 145 mm f/2.5 lens with MINTRON CCD camera, exposure  about 2-3 seconds. The photographer was experi-menting with the automatic light control setting and manual gain control - the reason why the image quality was not as desired.

The Space Station and Space Shuttle

Photo credit and information: Greg Roberts.

These are video images of passes of the International Space Station (left) and the Space Shuttle (right). The station appears so large that the photographer was able to resolve the image if a very short exposure was used.

The Tethered TiPS satellite

Photo credit and information: Greg Roberts.

This is an image of the TiPS satellite: two small masses, called Ralph and Norton, connected by a 4 km long tether - quite a faint object (usually around magnitude 9) except when the masses did a flash.

Unfortunately the tether broke in August 2006 and the satellite pair is now lost.

Click on image for larger version with more details.

More information about TiPS on the Internet.

The Orion Nebula captured on Video

Photo credit and information (M42) : Greg Roberts.

Description: The surveillance camera used by Greg was sensitive towards the infra-red [part of the spectrum]. The photographer worked with lenses at maximum aperture to get as much light as possible, so optical imperfections in the lens do show up (coma/astimatism/non-uniform scale etc). This is no problem for satellite work, but doesn't give masterpiece images otherwise .

A reflector performs somewhat better and the two images at the left show Messier 42 - the Great Orion Nebula - taken with a 6 inch f/5 Celestron reflector at the focal plane. The overexposed image (top) is the result of a few frames stacked, whilst the less exposed image (bottom) is a single frame.

Note these images are taken from Pinelands, in the middle of Cape Town and bright city lit skies - with a dark sky like Sutherland, another two magnitudes might have been seen!

With the 145 mm lens the photographer regularly works down to about magnitude 12, whilst the 6 inch reflector reaches about magnitude 16 - since satellites are moving he can't use long exposures so these magnitude limits are about what he sees in "real time" on the monitor screen with a maximum integration time of 2.56 seconds.

The popular saying in video photography circles is that a decent video camera will effectively "increase" your aperture by 5x and he has no reason to doubt this. With the 30 inch reflector at Sutherland, using an image intensifier, he had difficulty seeing 15th-16th magnitude stars - with the 6 inch under Cape Town skies its not a problem. Such is technology!

The 6 ASTRA Geostationary Satellites

Photo credit and information: Greg Roberts. 6 Feb 2007
The camera used was a 145 mm telephoto working at f/2.5 and a MINTRON camera, exposure 2.52 seconds. This is an "accumulated" image - in the same way as the program STARTRAILS is used, only for video devices and not still cameras.

The frames were accumulated for a total of 1 minute - what the program does is to remember the pixel count from each pixel in each frame and at the end of the one minute sumnation it displays the picture with the max pixel count for each pixel from the approx. 60/2.52 = ~ 23 or 24 images.
The mount was an alt/azimuth under control of Willie Koort's CoSaTrak program, so there is some field rotation during exposure.

More on satellite tracking and video astrophotography on Willie Koorts' homepage



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