On Saturday, April 26, 2008, at 11:28PM, <mmagid3005@xxxxxxx> wrote: >Thanks for the link, Adrienne. Those are really interesting photos. Does >Anyone know the math for calculating the exposure time if you want an arc >length X of the sun's path on the paper while using a Y focal length lens? > > > >Marty > Marty Heres an approximation for the math: The sun travels approximately 360 degrees/day which is 15 degrees per hour. We may assume the lens is focused at infinity, so that the sun and whatever else is in the landscape is in focus. This gives us Length of path on film=Focal length*SIN( (15) * (Time in hours) ) There are a number of good ways to estimate angles on the following web page: http://www.austinastro.org/angles.htmlhttp://www.austinastro.org/angles.html These could be useful in working out how far the sun will have traveled across the field of view after an hours exposure or whatever. I hope this helps, all the best Larry Cuffe ============================================================================================================= To unsubscribe from this list, go to www.freelists.org and logon to your account (the same e-mail address and password you set-up when you subscribed,) and unsubscribe from there.