For a digital camera - to accurately calibrate the actual time a camera puts in the image file the solution is in essence to photograph a clock. The catch is you need to do this for long exposures because the digital camera may do several operations (open shutter, expose, close shutter, possibly expose a dark frame for possibly another several seconds, convert to jpeg, then write to memory). So you need a type of clock that is accurate, that changes, but that is readable on long exposures (like 1 or 2 seconds). Ideally you want a clock that puts out some kind of moving lit pattern on a black background similar to a brightly lit second hand on a black background but hopefully much faster than a second hand. It is also interesting to take short exposures of a clock to see if there is a delay in the time code related to jpeg conversion or something else. - George Roberts http://gr5.org ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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