The Introduction of Tech Pan film at the UK Schmidt Telescope

Quentin A Parker , David Malin, PASA, 16 (3), 288.

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Historical Background

Kodak Technical Pan (Tech Pan) is a fine-grained panchromatic emulsion produced since the early 1980s (Kodak 1981), though it was introduced somewhat earlier as 35mm solar patrol film (as special order SO-115). Available in a variety of small film formats, Tech Pan has been more recently made on thick ($178\mu$m) polyestar (`Estar') base in larger sizes suitable for use in large Schmidt telescopes. The thick base film product is known as Tech Pan type 4415. Coatings have also been produced on glass as special product 153-01. In all cases the emulsion is believed to be identical, though overcoats, coating weights and emulsion hardening may vary.

The film-based material, particularly the 35mm format, has been used by the amateur astronomy community for many years with great success (Martys 1984 and 1991). Smaller, professional telescopes have also used the film for specific purposes, e.g. asteroid studies with the Uppsala and Palomar 18 inch Schmidt telescopes (McNaught, Helin, private communications). The product's versatility is demonstrated by its use in professional astronomical photo-labs for photomicrography (Roberton 1984) and contrast enhanced copying (Hadley 1984 and Martys 1982). Though its potential as an astronomical detector was appreciated by Everhard (1981), tests at professional observatories were discontinued when the on-glass material did not respond to standard gas-phase hypersensitisation. At this time, large film sizes were not available, and even if they had been, they could not be readily accommodated at the curved focal surfaces of Schmidt telescopes.

The first successful UKST exposure of Tech Pan film was in March 1991 though routine use did not begin until 1992 when several remaining technical difficulties were overcome. Once appropriate hypersensitisation and other procedures were adopted (see below), sky-limited Tech Pan exposures were obtained with the red band OG590 (`OR') filter with exposure times similar to those used for equivalent IIIa-F plates. These films gave better imaging, finer resolution and were about 1 magnitude deeper than standard IIIa-F exposures to which they seem superior in almost every respect. Tech Pan has now replaced IIIa-F for most applications (with the exception of ongoing surveys) and accounts for 70 percent of all UKST non-survey work since 1992. Over 1400 film exposures have now been taken (as of March 1999) and, since January 1997, 60% of all exposures are on Tech Pan. An exciting variety of Tech Pan-based projects are now underway including the new AAO/UKST H$\alpha$ survey of the Galactic Plane (Parker & Phillipps 1998a, 1998b). Such projects have offered a new lease of life for deep, wide field astrophotography with the UKST.

This paper details the background work that underlies this success and describes the remarkable properties of the emulsion by means of comparisons with what was the emulsion of choice for red light exposures, IIIa-F. The promising behaviour of Tech Pan in other wave-bands is the subject of an associated paper (Parker & Lee 1999, in preparation), and the colour equations that relate Tech Pan photometric behaviour to the equivalent IIIa-F emulsion are given in Morgan and Parker (1998). Finally, the astronomical utility of the emulsion, including estimates of its DQE (10%), are described in detail by Parker et al. (1999).


Next Section: Properties of Tech Pan
Title/Abstract Page: The Introduction of Tech
Previous Section: The Introduction of Tech
Contents Page: Volume 16, Number 3

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