PISES OBSERVATORY, May 2006 (Page 2)

The first ligth has been achieved using this setup.The optical system has been aligned with a laser, providing a perfect optical alignement at the first shot !

The next image is NGC4257, a self camera guided 180s binned 2x2 image (1.67 arcsec per pixel).

The image shows that the field corrector is well aligned and working perfectly, nevertheless, some ghosts from bright stars are visible : this is due to the field corrector, and can be cured by the use of an IR block filter.

The image display sharp stars and will allow good quality data. Star FWHM is 2.1 pixels leading to 3.7 arcsec resolution.

Focal length is 2198 mm (measured by astrometric data reduction)

Limiting magnitude

The limiting magnitude with a single 180s exposure, binned 2x2 is more than 20, the sky brightness have been mesured to be 19.8 per arcsec square (h=54° toward West, moonless night, hSun = -15°). Another measurment, later in the night hexibited magnitude 20.40 per arsec square, at 64° elevation, where the Sun was at -21° degree below horizon.

Tracking

The mount does not provide good tracking, the camera can guide and compensate for the large periodic error from the mount.
The periodic error is about +/- 10 arsec, and goes up to +/- 15 arsec within 190s of time.
The periodic error is not regular, has distorsion

Such a large error (up to 30 arsec) can be compensated by the internal CCD guider, if 1sec exposure time is used. Above the system cannot compensate for the fast movement from the star.

Tracking mechanics shall be totaly redesigned and refurbished.

Site light pollution

Light pollution as anywhere in France is a threat for Astronimical observation. There is no local pollution,

A Canon 20D and a Peleng fish eye have been used (see here for deeper tests) the next images were not processed from flat dans dark frame removal.

Fish eye image, from Est to West horizon (71 sec exposure time). The light poolution is visible nearby the horizon. The light pollution comes from cities like, Ales, Nimes, Montpellier and all their suburbs.

Fish eye image, from West, North to East horizon (100 sec exposure time),this part is very dark since there is no large city !