Long Exposure Theory
![Nautical Dawn [Cropped Version]](http://farm2.static.flickr.com/1133/1247663977_5863fc0c24.jpg)
When out doing night photography like the shot above, you don’t want to waste time guessing what the exposure time should be (like I did here one bank holiday morning…)
The technique I use is to do a shot at a very high ISO speed and a smallish exposure time, then use that to adjust for composition and check the histogram. Changing the ISO from 1600 to 800 (for example, doubles the exposure time. So to get back down to ISO 100 requires a few doublings to get the right number.
So I made a table to go in my camera bag for reference. Mainly because I’m lazy and rotten at Maths!
| 3200 | 1600 | 800 | 400 | 200 | 100 | |
| 1s | 2s | 4s | 8s | 16s | 32s | |
| 10s | 20s | 40s | 1min20 | 1min20 | 5min20 | |
| 15s | 30s | 1min | 2min | 4min | 8min | |
| 20s | 40s | 1min20 | 2min40 | 5min20 | 10min40 | |
| 30s | 1min | 2min | 4min | 8min | 16min | |
| 1min | 2min | 4min | 8min | 16min | 32min | |
| 2min | 4min | 8min | 16min | 32min | 64min | |
| 5min | 10min | 20min | 40min | 80min | 160min | |
Now I can’t imagine where the hell you would have to go to do a 5min exposure at 3200 ISO but its there anyway!
So in essence the table shows that if you did a 20 second exposure at 1600 ISO, you would have to do 5 minutes and 20 seconds worth to get the same amount of light in at 100 ISO.
Yes!! Thanks you! I finally find what I wont. And yes I need 20 sec. exposure at 1600 ISO
) Very nice table.
Sorry on my bad English grammar-Thanks!
uupss! I forget something. What if I want to change aperture?? How to calculate this?
Me again, I find this link http://www.fredparker.com/ultexp1.htm and I think that we could calculate something with this chart.
Aperture works the same. Keep the ISO the same and for each full aperture stop the shutter speed halves or doubles. And yes Freds computer chart explains the same thing but in more detail..
Example in theory: We want to shoot dark night.
If we need f/22 with 3200 ISO and for that speed of film and aperture we need 16 min. exposure.
Now if we use your table and change to ISO 100, the exposure time will be 80 min.
stevencastle,
Thanks you!
Don’t shoot night at f22!! … and 3200 ISO will be so noisy it will be a waste of time!
3200 ISO @ f22 = 16 minutes
is the same as
200 ISO @ f4 = 8 minutes
That will give you the same exposure but less noise and half the time!
Thanks,
)
I don’t want to shoot at 3200ISO I just speak theoretically.
Yes I want to shoot with 200 ISO but I want smallest aperture 11, 16 or 22.