WIDE FIELD ASTROPHOTOGRAPHY 3 By Chris Schur Here in this lecture we will discuss the mechanical aspects of piggyback work along with the proper method of polar alignment and guiding. Steps to do Wide field photography. The simple arrangement of an ordinary camera mounted piggyback style on an average equatorially mounted telescope allows many amateurs to attempt skyshooting for the very first time. The most basic requirements are to have a 35mm. camera with a suitable lens, and a tracking platform. This can be a barn door type mount or better, an equatorially mounted telescope with a camera bracket affixed to its tube. After the mounting is well polar aligned and tracking on a suitably bright guide star that is contained within the cameras field of view, the shutter is opened say for ten or fifteen minutes. The guidestar is then kept reasonably centered in the field during the exposure. The shutter is then closed, film advanced, and in a short time a collection of constellation shots or overlapping Milky Way fields can be obtained. To get the most from every shot, lets back up a bit and consider each step carefully to make the finals result the best they can be. Lets start with that polar alignment. Even a degree off the true pole will ruin an exposure taken in the higher declinations due to a phenomenon called "field rotation". This causes the entire photographic field to rotate around the guide star. In a wide 35mm. or 50mm. lens shot, this can obliterate the fine details in the outer half of the field! To prevent this, a polar alignment within a quarter of a degree is desirable. Over the years, there have been many complex methods to get the axis of the telescope aimed at the exact pole. However, we use a method that has proven effective and takes only about five minutes or less. Unlike the classic method of waiting around for hours watching the guide star drift to and fro to determine weather you are East or North of the true pole, there is a method which is much simpler. You can aim the RA shaft directly at the pole with an offset bore site. To accomplish this you will need a 6x30 finder, and a " V " block to rest on the polar shaft of the mounting. The finder rests in the other side of the " V " block, and the whole mount is aimed right at the pole directly using the chart in Burnhams Celestial Handbook or Uranametria 2000 for reference. Depending on your patience, you can home right in on the North or South celestial pole in a comparatively short time. Another consideration is the mounting of the camera on the back of your scope. Care should be given to the rigidity of the attachment. A simple ball joint mount available in many well stocked camera stores will work well for 35mm. and 50mm. lenses, but for anything longer in focal length some additional support is a essential. Even a short wooden brace holding the front of the lens will work well, and you should be able to move the entire telescope around by grabbing a hold of the camera lens itself. There should be no bending, vibration or slow shifting between the two optical systems. Also critical to the success of an astronomical photograph, is how carefully you guide. This can be made overly complex, but it shouldn't be. A typical arrangement is a 12mm. red LED illuminated crosshair eyepiece, and a 2x barlow for longer lenses. For 35mm. and 50mm. lenses, 50x to 100x magnification will be required with todays finer grained films. For 135mm.- 200mm., 100 - 150 power is suggested, and for up to 400mm. long lenses, you may need to go up to 200x for best results. Piggyback wide field astrophotography is one of the simplest yet one of the most rewarding aspects of the hobby. Whether you are well seasoned in the field, or a complete novice, you will always find yourself pouring over the prints or slides looking for ever fainter details you may have missed the first time through.