Archived posting to the Leica Users Group, 2002/07/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Good Afternoon Alan Trying to catch great night images of the sky is fun but can be frustrating. Allow me to point you to a link that carries the results of many different people using lots of different films and cameras. http://science.nasa.gov/spaceweather/meteors/gallery_18nov01_page5.html There are some truly amazing images there. A book reference I recommend is "Astrophotography 2nd ed Featuring the Fx system of Exposure determination." by Barry Gordon. It really covers the topic well. If I can paraphrase it. More exposure (more time, faster film, bigger aperature ) equals more stars Limits are 1) time - if you are on a fixed tripod, the earth moves and stars trail. For Pics without trails estimate at 500 to 700 seconds/lens focal length . Thus a 35 mm lens gives 500/35 or 14 seconds. Use 700 if you point towards the north pole. Much more time than that and you can start to see some trailing of stars. That may not bother you and the longer time greatly increases the likely hood of catching something unusual. This has limits too. See below. 2)time again - the sky has a brightness and will eventually fog the film. You can go to longer exposures with longer focal lengths before its a problem. In a good dark spot with a 35 mm f2.8 and 400 ASA film you can go about 20 minutes before the film is up to zone 5 or so. To keep the sky black you might want to drop down towards 5 minutes. By then the stars will have trailed out significantly. 3) time - How long will the camera stay open on 'B' 4) Some meteors are not meteors, they are satellites and airplanes. Airplanes blink regularly. Not all of them can be heard. Satellites move across the sky in about 3-6 minutes and if they are tumbling in orbit they may blink as well. Then there are Iridium Flares. Short of the moon and some really good meteors, they are the brightest things up there. They move fast and last about 3-5 seconds. See this site for predicitions. http://www.heavens-above.com/ There is no problem using the anonymous login. 5) We also have to be aware of UFOs and Elvis. The odds are increased if you X-ray the film ahead of time (microwaveing should do it too, folding undeveloped negatives tends to bring out crescent shaped UFOs) or increase your body load of single malt scotch - odd how that theme keeps reappearing! Lastly, try and get comfortable, lie down or recline and look up for a while. There are mysteries and miracles up there to be seen. Enjoy John Bohner Who saw the 2001 Leonid meteor storm from the desert and will never be the same. - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html