Test observations using Intes Alter M703

Intes M703 is a 180mm aperture maksutov-cassegrain telescope, the focal length is 180 mm (F/10). Some optical tests had been carried out previously here showing a very good optical quality. An E2V backside illuminated 47-10 CCD (13x13µm, 13x13mm CCD) has been installed at the telescope focal plane.

The plate scale is 1.48 arcsec per pixel, and the field is 25x25 arcmin. The telescope has been installed in a balcony, in the middle of Elancourt city (France) which is located 25 km from Paris, leading to a large sky background. This night, the sky background has been measured at a level of magnitude 16.7 per arsec square (400-1.0µm wavelength). The sky background is 10 to 15 times more luminous than a good dark sky...only up to magnitude 3 stars are visible. The countryside skybackground is about magnitude 19-19.5 per arcsec square.

The optical quality over the whole field is very good. No coma has been detected, the focal length has been measured (Astrometry) : 1801.5 mm. This link shows the optical quality using 10s exposure over the whole 1024x1024 CCD. The mean FWHM is 2.7 pixels (4 arcsec), and mainly limited by seeing.

The detection, has been measured also : magnitude 17 using a 120s exposure.

The telescope was aimed to the asteroid 1313 BERNA. 30x4s exposure has been recorded at 20/02/2004 - 23h21m30s before the sky become overcast. The magnitude has been mesured to 15.04 (Flux = 7593 ADUs).

note : tracking not so good because of a not so good telescope polar alignement.

As a conclusion, despite the fact that the telescope is located in a very bad place for deep sky astronomy, some interesting work can be achieved because the field of view is about 25x25 arcmin, the CCD is a backside illuminated one, and the F/10 helps to reduce the effect of a large sky background.

By Cyril Cavadore, Fev 2004