How do you meter exposures > 30 seconds?

Discussion in 'Photography Beginners' Forum' started by Riggaberto, Mar 17, 2007.

  1. Riggaberto

    Riggaberto TPF Noob!

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    The farthest my camera goes before bulb is 30 seconds, so I was wondering how one meters such situations? I assume you have to get a light meter, and I have one, but it's really old and it doesn't go past 4 seconds.

    So can someone show me an example of the right light meter to get, or tell me a trick to use my in camera meter to figure out how long I have to expose a scene with bulb?

    Thanks!
     
  2. cosmonaut

    cosmonaut No longer a newbie, moving up!

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    Why do you want to go beyond 30sec? I shot at night and it is rare that I go that far. You can always bump up the iso or open the aperature a bit. I think you could meter it at a high iso and then just use math to figure it. 30 sec at 100iso will equal 15sec at 200 then 7.5sec at 400 ect. Also if your camera will only go 30sec you will have to have a stop watch.

    Cosmo
     
  3. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    You can open up the aperture and/or raise the ISO until you get 30 sec or less. Then calculate how many stops underexposed your settings are compared to where you really want to be. 30 sec times 2 for every stop.

    Example: I want to shoot at night at ISO 100 & f/8. I set the camera to ISO 3200 and f/2.8 and take a meter reading. At those settings if it says the shutter should be 30 sec, then to get the exposure time for ISO 100 & f/8 I count stops.

    ISO: 100 200 400 800 1600 3200
    aperture: f/2.8 4 5.6 8 11 16 22 32

    8 stops between ISO 100 & f/8 and ISO 3200 & f/2.8

    30 sec x2 x2 x2 x2 x2 x2 x2 x2 = 2 hours and 8 minutes (assuming no reciprocity failure)
     
  4. fightheheathens

    fightheheathens TPF Noob!

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    In my experience, once you go past 30 or so seconds it more just about guess work and your own experience.
    I often use ksmattfish's method when i can get an exposure reading, But if it is too dark even to do that i guess and bracket +- one stop in each direction. with film's lattitude you have quite a bit of error room if you go that way. i think digital is less forgiving though.

    also as important note, once you are in these long exposures accuracy is not as important. the difference between a 1 min exposure and a 1 min 10 second exposure is not really going to be visible to our eyes so even just a watch with a second hand would work


    so what i am saying is that you dont really need a seperate light meter for longer then 30 second exposures.
     
  5. Torus34

    Torus34 No longer a newbie, moving up!

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    I use an old Gossen Luna Pro. While it can take me up to exposures measured in hours, I still bracket upward once I get past 30 seconds or so. [B&W film]
     
  6. fmw

    fmw No longer a newbie, moving up!

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    I'm with Heavens on this one. Remember light meters want to reduce the subject to medium gray on the tonal scale. You want night shots to look like they are taken at night, not in the daylight, so the meter will tend to want to overexpose everything by at least a couple of stops.

    Guessing and experience are good. Braketing also helps. In all the years I've done photography, I've never taken a meter reading of more than a couple of minutes (2 stops from 30 seconds.) Anything longer has always been using the "wet thumb in the air" method.
     
  7. Alex_B

    Alex_B No longer a newbie, moving up!

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    True, roughly guessing exposure often works very well at night.

    To be creative, to depict motion, many reasons.
     
  8. This has also been made easier by shooting digital. Because you're set up for shot anyway (tri-pod out, camera mounted, small foreign cigar tucked in the corner of your mouth) you may as well try several exposures. The display on the back will show you whether you got close, and then you bracket the shot - one a little longer, one slightly shorter. With film you didn't want to burn through a whole roll while stabbing at exposures, but with digital a bad result won't matter as much, now that you've already spent the money on the camera and memory cards...
     
  9. OOooops. Disreagrd my previous post. Should have checked your Profile BEFORE posting... you shoot film.

    Do bring a cigar though.
     
  10. xfloggingkylex

    xfloggingkylex TPF Noob!

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    there is an image in the april edition of pop photo that displays a picture taken of the north start and surrounding starts, exposed for 12 hours. The stars make most of the full journey around the earth, but daylight was coming so the exposure had to be stopped.

    guessing is about all you can do for that.
     
  11. Garbz

    Garbz No longer a newbie, moving up!

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    What do you want to take photos of? If you want to take photos of a city at night time then guessing based on the above rules works well. If there are quite a few lights available a centre weighted metre can often hit it dead on. If you are close to the lights then you may find the calculated value to short, and if there are no lights you may find it too long.

    Night photography with film is mostly guess work though. Film changes dramatically after you get to some longer exposures. The colour cast changes, the light sensitivity changes. For instance I took a photo of a skyscraper once on ISO400 film. It was the last in the roll and swapped it out for ISO100. I simply used the same exposure and bracketed 2 stops and the photo turned out VERY different.: http://i12.photobucket.com/albums/a241/Garbz01/junk/film.jpg The 400 is on the left.

    As for shooting stars. The star trail lengths are maths, as for the exposure that is guess work. I can not take a photo longer than 2 hours here or the sky completely blows out my picture. Too much light pollution.
     
  12. Groupcaptainbonzo

    Groupcaptainbonzo TPF Noob!

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    30 Seconds is a VERY long time. Even with a good tripod you will be lucky to get away without noticeable camera shake. In a house you may well be shielded from the elements, but people walking around will vibrate the floor boards . So you really have to plan this out. If time lapse is important then you will have to bite the bullet.
    REMEMBER with film you will encounter reciprocity law failure. When every one has been telling you that f8 at 1/100th is the same as f5.6 At 1/50th, that is reciprocity law (the exposure is the reciprocal of the time). Once you get above about 10 seconds the different layers of the emulsion reach a point of saturation (although this happens at different time for different parts of different emulsions). and the sums all go out of the window.... You will be able to find tables which will help you to calculate the amendments to the exposure time by going on the film manufactures web sites and looking for the tech specs of the film you wish to use (although as you tend to add a stop here and a stop there you get into some astronomical exposure times..)..
    Otherwise, I'd go with FMWs suggestion of the "wet thumb in the air" school of presision...
     

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