Long exposures during the day

Discussion in 'Beyond the Basics' started by mox, Nov 21, 2004.

  1. mox

    mox TPF Noob!

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    I want to take long exposures during the day.

    There is many solutions like changing the f-stop to something like f/22 but still I can only do ~1-2 secondes at ISO100

    I've been told to use a Neutral Gray Filter (+8) wich is doing EXACTLY what I want

    But I was thinking.. what if I use two Polarizing filter ? You know, when you put a polarizing filter in front of an other one.. if you turn one of them, you change the 'transparency'... can this gives the same effect as a Neutral Gray Filter ?
     
  2. ksmattfish

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

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    A polarizer blocks about 2 stops of light, which would adjust your 2 sec @ f/22 to something like 8 sec @ f/22, or even more time with reciprocity failure (see your film manufacturer's website for long exposure adjustments). You could stack filters, or choose a lower ISO to get even more time.
     
  3. mox

    mox TPF Noob!

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    btw, I have a DSRL Canon 10D and the minimum iso is 100
     
  4. tr0gd0o0r

    tr0gd0o0r TPF Noob!

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    You may run into some noise problems w/ a DSLR with longer shutter speeds like that.


     
  5. Digital Matt

    Digital Matt alter ego: Analog Matt

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    You will have no noise problems at ISO 100 on a 10D and several seconds of exposure. You can do exposures of probably 10-15 minutes with no real problems, and noise can be dealt with in a longer exposure.
     
  6. ksmattfish

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

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    Good question. I think it would be different.
     
  7. j_mcquillen

    j_mcquillen TPF Noob!

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    I don't think using two polarising filters will be the best option for you here...

    Yes, it will cut out a lot of light to the lens, but with 2 polarising filters stacked up, you'll risk vignetting as the edges of the filters intrude into your image, and increased lens flare as light bounces around between the multiple surfaces - far better to use a single flat Neutal Density grey filter - you can buy types that will probably cut out more light than 2 polarisers anyway.

    Remember with photographic polariser filters, the effect you describe (of changing the 'tansparency' - darkening skies, and cutting out reflections)occurs with only one filter neccessary.
     
  8. Unimaxium

    Unimaxium TPF Noob!

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    Regarding film, I thought reciprocity only breaks down when you get up closer to 1 minute, but not as short as 8 seconds (and on the other end, faster than 1/10,000th). I could be wrong, as I've never really had experience with long or fast exposures, but I thought that was what I heard.
     
  9. Hertz van Rental

    Hertz van Rental TPF Noob!

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    The exposure durations at which reciprocity effects occur vary with the type of emulsion. Reciprocity is not normally a problem with 'normal' b&w films* but is much more of a problem for colour film.
    Always refer to the manufacturers data sheets.


    *Kodak recommend that development and exposure compensation is made for exposures shorter than 1/2000 of a second or longer than 1/2 of a second.
     

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