An automated system to measure and analyse large numbers of objective prism spectra from photographic plates using the Automated Plate Measuring (APM) facility at Cambridge is described. The system is being applied in a number of ways including automated quasar detection and subsequent clustering analyses, galaxy redshift surveys, and wide field searches for rare objects, such as carbon stars.

If T-grain Technology can be used to manufacture emulsions of astrcj nomical type, it will provide a better Detective Quantum Efficiency than any existing plate. As Dr. Millikan explains us, this increase in D.Q.E. can result in an increase in Signal to Noise ratio (i.e. increase in coil trast or decrease in granularity) or in an increase of plate speed. As Kodak and we, their customers, don’t have a lot of money to spend for three or more new emulsions, we have now to choose for a new emulsion, which might be a harder one (more contrast), a finer one (better granularity), or a faster one.

The UK 1.2 metre Schmidt Telescope at Siding Spring Observatory, Australia, has taken about 8500 plates since it was commissioned in 1973. A large fraction of these plates, including those for the southern and equatorial Sky Surveys, are on Eastman Kodak Illa-J emulsion. A significant number of these processed Illa-J plates have developed many small gold spots similar in size to faint star images. They are most likely to occur in areas of relatively high density, such as in bright star images or on the stepwedges, and are sometimes scattered around in non-image areas (fig. 1). An alarmingly high proportion of plates taken in 1974-75 (about 50 per cent) have developed gold spots, and the most recent affected plate found so far is J6517, taken in October 1980. Four early IIIa-F plates have also been found to have gold spots.

By applying the principle that all stellar image profiles should be identical apart from a scale change, we can derive a relative calibration for a photographic plate without use of calibration spots or other indirect means.

The International Halley Watch Wide Field Network for Large-scale Phenomena (Niedner, Rahe and Brandt, 1982) will be receiving several thousand original or first copy images of the large scale structure of comet Halley. These images will be coming from over 90 telescopes at 70 different observatories around the world. Some but not all of the photographic material will have associated sensitometry. It is anticipated that since this network is looking for changes in the plasma tail structure most, if not all, observations will be made with unfiltered Kodak IIa0 emulsion. One of the major tasks of the network will be to study the plasma tail variations at the highest time resolution possible. In order to do this, it will be necessary to combine photographs taken at many observatories.

The 2020GM PDS microdensitometer of Perkin-Elmer, Optical Division, was installed at Muenster University during the summer of 1982. The present communication summarizes the greater part of work performed during its first year of operation and outlines plans for the future. The microdensitometer and the system configuration are shown in Figs. 1 and 2.

A new photographic measuring machine is under construction at Paris Observatory. The amount of transmitted light is measured by a linear array of 1024 photodiodes. Carriage control, data acquisition and on line processing are performed by microprocessors,a S.E.L. 32/27 computer, and an AP 120-B Array Processor. It is expected that a Schmidt telescope plate of size 360 mm square will be scanned in about one hour with pixel size of ten microns.

A 14-inch Schmidt plate contains 109 photographic grains and 105 to 106 images of stars and galaxies on it. Such a quantity of data is too large to be handled in a conventional way even for a big computer.

There is, in general, an alternative method to solve this problem; one is to store the data of all pixels on intermediate medium (e.g., magnetic tape), and reduce them into image parameters afterwards. The other method is to do all the processing simultaneously with the measurement. The latter is very useful for the automated detection of celestial images on large Schmidt plates.

The electrographic (E.G.) camera is one of the most powerful modern detectors having high sensitivity, extended spectral response, extreme spatial resolution, low background, no threshold, good linearity and large dynamic image. A combination of highly uniform electric and magnetic fields produces distortion-free and extremely sharp images which are recorded by electron sensitive emulsions (Figure 1).

The new detector MEPSICRON (microchannel electron position sensor with time resolution) is an image photomultiplier sensor for high spatial and time resolution, working in a photon counting regime. It has been especially designed for deep sky photometric pictures, for high resolution spectrophotometry with single or crossed dispersion spectrographs for long slit spectroscopic techniques, for high time resolution pictures and spectrophotometry especially related with speckles techniques and very fast varying sources as pulsars, and for Fabry-Pérot interferometry.

The potential of the Schmidt optical system, when combined with optical fibres and linear detectors, is assessed. Recent work on the use of optical fibres at the U.K. Schmidt Telescope is described together with anticipated developments. In conclusion, there is a speculative consideration of the construction of a large, altazimuth Schmidt telescope (LAST).

Calculations have been made of the intensity distribution of star images formed at the focal surface of large Schmidt telescopes. The calculations take account of atmaspheric seeing, aperture diffraction, manufacturing errors, chromatic errors in the corrector plate, scattering in the emulsion, photographic response and grain structure. The results are expressed in terms of simulated microdensitometer scans across the processed emulsion.

Results are given for a system S1(1.24m, f/2.5) similar to the 48" U.K. Schmidt (with both singlet and achromat corrector plates) for several combinations of correctors and filters using Illa-J emulsion for recording. The improvement in performance expected from the use of larger Schmidt telescopes is discussed and results are given for two designs with 2.5 metres aperture, S2(2.5m, f/2.5) and S3(2.5m, f/3).

Observational and geometric approaches to the problem of determining the vignetting function are discussed. A simple technique for producing a “flat-field” is described, and the various uses of such a flat-field to investigate the photometric accuracy and sensitivity of different emulsions are discussed.

One presents hereafter the HIPPARCOS satellite payload which is mainly constituted by a Schmidt telescope; a possible way to approximate the Schmidt mirror elliptic deformation profile is explained. Then, the signal expected from the optical chain is briefly described and one displays a residual chromatic effect which may introduce errors in the measure. To conclude, numerical values of this effect are given and one shows the necessity to take it into account in the data reduction process.

During the last ten years the Max-Planck-Institut fur Astronomie (MPIA) has installed four large telescopes at its observatory on Calar Alto, Spain, which is operated jointly with the Spanish National Commission for Astronomy as the German-Spanish Astronomical Center. Figure 1 shows the domes of the 1.2 m, 2.2 m, and 3.5 m telescopes of Ritchey-Chrétien type and the dome of the Schmidt Telescope. They all are Zeiss telescopes, the former three coming from Oberkochen, the latter one from Jena.

The 50/70 Schmidt telescope at the National Astronomical Observatory (NAO), Bulgarian Academy of Sciences, is an example of the possibilities for a long-term operation and everlasting actuality of these types of telescopes. Originally, this telescope was constructed in the GDR in 1952 and mounted in the Potsdam Observatory, Academy of Sciences of the GDR (as such, it is on the list of West, 1974). In 1979, on the basis of a mutual agreement between the Bulgarian Academy of Sciences and the Academy of Sciences of the GDR, it was transferred to Rozhen, Bulgaria. The principal parameters of the instrument are as follows: I. Main mirror: diameter: 70cm; material: Tempax; thickness in the centre: 10 cm; radius of curvature: 344 cm.

The Torun Schmidt telescope and its scientific applications are described. A special attention is given to the Torun Objective Prism Sky Survey.

The ultraviolet-telescope satellite (UVSAT) project has been proposed to the Institute of Space and Astronautical Science (ISAS/Japan) by the UVSAT Working Group. The main telescope will be an F/4 Cassegrain with a 60cm primary mirror. A design study and some preliminary experiments of an intensified CCD camera with an objective spectroscopic capability are under way.

Photographic astrometry, including work with Schmidt telescopes, can be divided into two main fields, (i) the measurement of positions of objects relative to a reference frame of stars with known celestial coordinates, and (ii) the measurement of relative proper motions and trigonometric parallaxes from a series of plates taken on the same field. The former demands a knowledge of the absolute transformation between angles on the sky and measurements on a plate, whereas in the latter we are only interested in differential transformations from plate to plate. The potential value of Schmidt telescopes for both these fields of astrometry lies in the large area of sky and range of magnitude which can be imaged on a single plate. The former advantage is however, to some extent offset by the curvature of the focal surface which means that, in order to utilize the full field the plates must be constrained to the form of the focal surface during exposure.

The ESA Astrometry satellite Hipparcos is due to be launched in early 1988. It will measure very precise positions, parallaxes and proper motions for about 100 000 stars. However, in order to be included in the Input Catalogue, the programme stars should have positions and magnitudes known in advance with respective accuracies of about 1" and 0.5 magnitude. This will require new astrometric and photometric measurements and observations. Sky Survey Schmidt plates will be extensively used, especially for astrometric measurements in the Southern hemisphere.