Aller au contenu principal

The NAROO Project

Hardware

Figure below shows the NAROO digitizer as on 2021 January. The machine consists of a granite based Newport-Microcontrol open frame air-bearing XY positioning table, with a plate holder assembly suited for mounting glass plates up to 350-mm wide. The NAROO machine is able to process automatically almost all known transparent photographic material.

   
 

NAROO digitizing machine.

 

The granite base measures 1.3 m × 1.3 m × 0.2 m. It is mounted on dynamic feet to compensate for the building and environment vibrations. The position of the XY table is read by Heidenhain encoders. The linearity and orthogonality of XY-axes were calibrated by Newport-Microcontrol using a laser interferometer. The local XY table positioning and repeatability were measured by the manufacturer. The positioning stability was measured with a capacitance up to 10 nm, the repeatability (how closely the table can return to an initial position following movement over the entire X–Y) was measured with a capacitance of 45 nm.

In order to reach and maintain a high geometric and radiometric accuracy, the digitizer is placed in an overpressure air-conditioned ISO-5 clean room, at a temperature of 20°C ± 0.1°C and a relative humidity of 50 per cent RH ± 5 per cent RH.

Optics

The optical unit consists of an Andor Neo sCMOS Camera, mounted on a VST VS-TCM-130/S telecentric 1:1 objective. This system is attached to the Z-axis above the XY table. The photographic plates are illuminated from below with very bright Light Emitting Diode's LED, controlled by a high precision DC power supply. The complete optical system was specifically designed by the Instrumentation Pole of Paris Observatory to avoid any optical distortion.

Imaging process and products

Most of the NAROO functions are computer controlled. At the beginning of each plate digitization, the photographic plate is put automatically into focus by pressing the plate holder up to the counter pressure rack. The illumination is set to 3/4 of the saturation on the plate's sky background by adjusting the DC power supply unit to the LED. The plate is digitized automatically in step and stare mode with steps corresponding to user-defined moves in the X and Y directions. The time needed to digitize a single plate of 12 cm × 17 cm is 5 min. Mean dark and mean flat images are also computed to correct the individual raw plate images. An overall mosaic FITS image of the whole photographic plate is generated from the individual images with or without overlapping.

The 2D sCMOS Camera provides images with 2560 × 2160 pixels of 6.5 μm × 6.5 μm. The dynamic range is 30000:1. Each frame results in a 16-bit FITS file with 11 MB disk space. For instance, the digitization of a classical 5 x 7 inches Kodak plate will require about of 1.2 GB disk space, that of a Schmidt plate will be up to 5.9 GB.