How to Determine Reliable Intensities Using Film Methods?

Abstract

The basis of a successful structure analysis is to obtain reliable intensities. In the field of electron crystallography intensity data can be collected on-line with a CCD-camera as well as off-line using image plates or film material. Whereas image plates are read out with a laser, film material is analysed via a densitometer or digitised using a CCD-camera or a scanner. Both, CCD-camera and scanner, uses CCDtechnology and we show that both systems can be used for intensity evaluation. In order to obtain reliable intensities from film media it is important to define and calibrate the experimental conditions, the digitization process and the evaluation of intensity data exactly. A high optical resolution and a high optical range are necessary for a good evaluation.

For comparable CCD-chips the results obtained are similar. Due to the fast development in computer technology, the systems used here are no longer comparable to the high end products of today with 16 bit optical density and 3000 by 3000 dpi optical resolution but one can expect that both systems lead to similar results. Scanners are more easy to handle and so we prefer a high end transmission-scanner for intensity evaluation in the future.