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thomps6s
04-30-2008, 01:27 PM
Most cameras do not let you expose past 30 seconds unless you use Bulb mode and a Cable Release. The following is a write up on how to expose past 30 seconds.

If you have shot after sunset or before sunrise and see that your meter is blinking "30" that means it is too dark for the meter to get an accurate reading.
The following information will help you learn to expose manually to get the correct exposure.

Things needed:
a. Digital SLR
b. Tripod
c. Cable release or remote release

Assuming you are setup on your tripod, you have taken the time to line up your horizon making sure it is straight, locked in your focus point and are ready to click the shutter.
You see that at F/11 or higher the meter is showing a blinking 30 and not allowing you to take a picture.
Put your camera in bulb mode, lock the shutter and take a 60 second exposure.

For example, lets say your histogram looks like this after 60 seconds

http://farm3.static.flickr.com/2147/2069527216_444d348005.jpg

If your histogram looks like the one I linked to after a 60 second exposure, you can see it takes up approximately 1/4th of the histogram.
So in order to fill that histogram you would have to quadruple your exposure time.
(this will vary depending on how your histogram looks)
Which in this case, you started with 60 seconds, now quadruple that time. You now have a 240 seconds or 4 minute exposure time, roughly.
I say roughly, because, depending on how fast the light is fading, you may need to add a minute or more to that guess.

Watch your histogram, you do not want the blob of data to be touching the very right end of the histogram. This allows you to not blow out your highlights. (this is very important)

In the end it is a bit of a guessing game, but using this technique, you will get closer to a great exposure.

If I have confused you or you have questions, please ask.

Shawn M
04-30-2008, 02:43 PM
good tip/info
Thanks