[天文书籍]彗星对齐+星点对齐PS合成后处理教程.pdfVIP

Optimizing Images of Comets Optimizing Images of Comets Bernhard Hubl, 2006-10-30 1. INTRODUCTION One can reach very deep images of deep sky objects, if the telescope is guided onto the stars and if one chooses very long exposure times. The invested exposure time is only restricted by the patience of the photographer. There are two reasons, why the situation is totally different when imaging comets: 1. Comet structures can severely change in short time intervals. The changes in the comet tail restrict the maximum time interval for images to typically 1 hour. A too long time interval would result in a ‘washing out’ of comet structures. 2. Comets move fast across the sky. A guiding onto the stars leads to washed out comet structures after a few minutes. It is possible to guide onto the comet. This results in a sharp comet, but at the same time in star trails. This article describes my personal method of combining many images with short exposure time to create an image with a deep comet and sharp background stars. One example for this method is my image of comet Swan at 2006-10-26 ( /swan-2.htm ). Fig. 1 Comet Swan; 2006-10-26; NP101 with ST2000XM; 36 min exposure time comet_images.doc 2008-04-02 1 / 8 © Bernhard Hubl Optimizing Images of Comets 2. CREATION OF RAW IMAGES 2.1. Observation Planning A careful observation planning is the prerequisite for a successful image. The first step is the update of the comet ephemeredes using a planetarium software. My personal favourite is Guide8. It is important to know the apparent velocity of the comet. This velocity can be found in the last rows of the info window of Guide8 for comet Swan (Fig. 2). Comet Swan is moving with a velocity of 5.9’ per