Webcam & Telescopio

Le immagini qui sotto sono state riprese con una Logitech Quickcam VC ed elaborate con Iris o Registax

Luna

Marte

Giove

Saturno

Logitech QuickCam VC

(from Horst Meyerdierks’ web site: http://www.roe.ac.uk/~hme/webcam/ )

The Logitech QuickCam VC out of the box.

This webcam has 320x240 pixel (SIF size). It is better for pointlike as well as faint objects, so I would this for star fields and deep sky objects. Its advantages over the ToUcam Pro at VGA size are:

• Compression is not used in the data transfer from the webcam. Hence even stars do not cause compression artefacts in the images.
• The frame exposure can be up to an amazing 1.8 s. This means that per accumulated stack exposure time 40 times fewer frames need to be collected. Hence the noise level is lower.
• Virtually no time is lost between frames. Other webcams like the ToUcam Pro have a longest exposure that is five times less than the frame rate, leading ot a loss of 80 per cent of the elapsed time.

There are also disadvantages:

• Support under Linux is not quite as good as for the Philips webcams.
• The webcam has fewer pixels, reducing either the field of view or the resolving power.
• It is not very good at colour, which does not matter for grey deep sky imaging.
• The pixels are not square, but slightly smaller vertically than horizontally. This, too, does not matter very much.

The QuickCam VC has the following specification, as collated from a document "QuickCam Technical Information", which used to be on http://www.logitech.com, and from Michel Collart's AstroCam web site (http://www.astrocam.org/qcamvcUS.htm):

• CCD, 352x288 pixels, CIF sensor format
• 24 bit colour
• up to 30 frames per second AVI
• still formats BMP, TIFF, JPG
• CCD 362x291 pixels in total, diagonal size 0.2 inch
• operation at 0°C to 45°C, storage at -10°C to 70°C
• humidity 0 to 90 per cent non condensing
• lens is f/2.0 with 46° field of view
• shutter speed 0.1 ms to 20 ms
• pixel size 8.2 µm x 3.8 µm
• CCD size 2.9 mm x 2.2 mm
• sensibility 170 mV/lux

The detector diagonal quoted by Logitech is an overstatement, Collart's numbers make more sense. In the vertical direction there are probably two half-height pixels for different colours. This still leaves the vertical pixel size 7 per cent smaller than the horizontal pixel size. So circles will not be exact circles in the image output. I confirmed this experimentally: Images of Jupiter appear circular, indicating that the pixels deviate from squares by the same percentage as Jupiter deviates from being spherical (0.065). The Jupiter observation - assuming the focal length is known - also confirms the size of the pixels to be as listed by Collart.