Using long shutter speeds and bulb

Discussion in 'Beyond the Basics' started by kdabbagh, Feb 10, 2010.

  1. kdabbagh

    kdabbagh TPF Noob!

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    Hey all,

    This question has been on my mind for a while, and tomorrow I will start a two day camping trip in Egypt's White/Black Desert. I know it will be dark at night but I want to take photos of the camp/campfire and possibly star formations etc. Sometimes when I shoot with long shutter speeds my camera indicates that 30 seconds is not enough (the max I can go on my D90). I know how the bulb function works but I do not know how to calculate how long the shutter should be. Any thoughts?

    ..I will have a tripod and a remote with me.
     
  2. Stosh

    Stosh TPF Noob!

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    Lucky for you we're in the digital age and you can see instant results. Seriously, there is no way to really calculate what you'll need unless you have a low light light meter. And even with the meter the lighting situations are so difficult it probably wouldn't help you. Just experiment and/or bracket heavily. Campfires are different sizes and therefore different brightnesses. I doubt you'd need anything longer than 30s with the campfire. Your on-board meter should be able to help with that. The night sky has a HUGE range of brightness depending on whether or not the moon is up, and what phase it's in, and how much light pollution there is there.

    If you want to capture stars and/or star trails, there are lots of sites on techniques. To capture still stars, a good quick rule of thumb is take your focal length times # of seconds and that can't exceed 500. 50mm x 10s = 500. For high resolution shots you may want to shrink that number down to 200 or below which now becomes very difficult to even record good stars.
     
  3. davebmck

    davebmck TPF Noob!

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    I agree, you need to just experiment. Take a shot at a given setting and review your histogram. Keep making adjustments until your histogram indicates a proper exposure and the image on your lcd looks like you want it. Bracket that exposure and you will have some room to play in PP.
     
  4. Turnerea

    Turnerea TPF Noob!

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    I agree that you need to experiment, however don't rely on your histogram so much, depending on what you're trying to shoot. For instance if you are doing star formations (star trails I'm guessing with your setup) than the histogram isn't going to tell you much. Most of your pixels should be wayyy to the left even when you have a picture that looks pretty good as a star trail. So just keep that in mind... you're not looking for an average exposure there.
     
  5. LearnMyShot

    LearnMyShot TPF Noob!

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    You need to stay on the tripod and keep changing the exposure until you get the result you want by checking your screen...take your laptop and shoot tethered to see exactly what you're getting.
     

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