[pure-silver] Re: Sunburns photos

 
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
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