Calculating long exposure times
Janos wrote: Or with the camera's meter when you say max ISO are you talking about aperture is wide open at let's say 2.8, shutter is set to 30 seconds and I use my ISO setting to set exposure. Where the ISO lands that would be considered the max?
If your meter suggests 30 sec @ f/2.8 @ ISO 3200 that's the same exposure as 8 hours 32 min @ f/22 @ ISO 100. 6 stops between f/2.8 and f/22. 5 stops between ISO 3200 and ISO 100. 11 stops total. Start with 30 sec and double 11 times, and if my math is correct it's 8 hours and 32 min.
I do some night photography, but not star trails. As the Earth rotates at the same speed for everyone you should be able to find example photos of particular exposure lengths.
I'm usually trying to reduce exposure time which may not be a good idea for star trails. I use ISO 100, and then set my aperture as large as it will go to get what I want in my scene in focus. If there is nothing in the foreground close to the camera I may be able to use fairly large apertures. Look into hyperfocal distance if you aren't familiar.
EDIT: Whoops, I think 30 sec to 8 hrs 32 min is only 10 stops. Double it again for 11 stops.
Matthew L Kees
MLK Studios Photography School
www.MLKstudios.com
[email protected]
"Every artist, was once an amateur"
Canon EOS 7D|Canon EF 70-200mm F/2.8L USM |
Canon EF 50mm F/1.4 USM |
(2) Canon Speedlite 480EX II
Show us some results.Janos wrote: Yeah this worked! Just wanted to say thanks again for the help.
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