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  1. #1
    Karl K's Avatar
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    How to make an eight hour exposure...

    Help is needed before I go out for this shoot. I am planning to photograph the interior of Grand Central Terminal's Main Floor. My camera will be situated next to one of the main staircases on either end, if I can get the necessary permit to set up a tripod for eight hours. The camera is a Leica M3. The lens is a 12mm Voigtlander. The film is Ilford SFX. Thanks to an APUG member, Simon R. Galley, I now have an Ilford SFX filter mounted in a Cokin P holder, which I will mount in front of the 12mm lens. I estimate that the average exposure during the eight hours is four seconds @f/22, without compensating for reciprocity failure and the 16X filter factor. I can only make one exposure in one day, so I want to get as close to a perfect exposure as I can. Does anybody have experience with this sort of thing? Can anyone calculate the correct exposure factor? Thanks in advance.

  2. #2

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    Do you plan on staying with the camera? Are your plans to have the image devoid of people? A long exposure will do that.

    Are you planning on the shutter remaining open for 8 hours or do you have some means of remotely or automatically tripping the shutter?

    Those are questions that immediately come to mind. There may be others.

    I have checked the Ilford site and find no reciprocity information on the film. I would recommend contacting them for guidance on this.

  3. #3
    Dave Parker's Avatar
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    I am a bit confused???? Are you going to be making one 8 hour exposure, on one frame of film, or several shorter exposures over an 8 hour period on one frame of film, or several exposures over 8 hours on different frames of film?

  4. #4
    Karl K's Avatar
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    Quote Originally Posted by Donald Miller
    Do you plan on staying with the camera? Are your plans to have the image devoid of people? A long exposure will do that.

    Are you planning on the shutter remaining open for 8 hours or do you have some means of remotely or automatically tripping the shutter?

    Those are questions that immediately come to mind. There may be others.

    I have checked the Ilford site and find no reciprocity information on the film. I would recommend contacting them for guidance on this.

    Yes, of course I plan to stay with my Leica...this is NYC, after all!

  5. #5
    Karl K's Avatar
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    Quote Originally Posted by Satinsnow
    I am a bit confused???? Are you going to be making one 8 hour exposure, on one frame of film, or several shorter exposures over an 8 hour period on one frame of film, or several exposures over 8 hours on different frames of film?

    This is a one exposure assignment, so that Grand Central Station will be completely devoid of people, except for that homeless guy who is asleep in the corner and will remain there for the entire eight-hour exposure.

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    I don't really get your initial point. You speak about an 8 hour exposure, but you also mention a 4 second exposure at f22.

    I bet that with an exposure of 8 hours, the reciprocity failure correction must be within the scale of days ;-) What f-stop do you plan to use? f1024?
    Is it the filter that requires that much compensation?

    I've got the data here for FP4/HP5 (same factors): 30 seconds exposure will become 157 seconds with reciprocity correction.
    I have NO idea what SFX with a filter and its correction will require... Ilford.com does not mention anything about it: http://www.ilford.com/html/us_english/pdf/sfx200.pdf

    G

  7. #7

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    Unless the assignment explicitly calls for an 8 hour exposure, I strongly recommend shooting wider open and getting the time down to the one hour (at most) area. That should still get rid of the people for you while giving you time to bracket. I once shot a scene that required an unfiltered 5 hour exposure at f11 and it was a nightmare ...took me three attempts/days to get it right. Seriously, try to get your time down.

  8. #8
    reellis67's Avatar
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    Quote Originally Posted by Karl K
    ... I estimate that the average exposure during the eight hours is four seconds @f/22, without compensating for reciprocity failure and the 16X filter factor...
    This seems to be what is confusing people, at least it is confusing to me. Is the base expsoure, meaning no filter factor and no reciprocity, 4 seconds at f/22? The way it is phrased in your question is a bit confusing but I think that that's what you are saying.

    If so, I think that you will need to add some neutral density as well, because even with a 4 stop filter, you are looking at 64 seconds if I did the math correctly.

    I have notes on Ilford traditional black and white films having a 1.6x reciprocity factor for long exposures, so let assume it's the same for SFX (your guess is as good as mine, perhaps better!) so this will give you 102.4 seconds @ f/22. So now we have something like 1.7 hours. If you added ND to give an additional 1 stop change, you would be around 3.4 hours, and ND for 2 stops would land you around 6.8 hours- pretty close...

    Please feel free to correct me on any of this - I rarely do exposures longer than a handful of seconds...

    - Randy

  9. #9
    Dave Parker's Avatar
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    Quote Originally Posted by reellis67
    This seems to be what is confusing people, at least it is confusing to me. Is the base expsoure, meaning no filter factor and no reciprocity, 4 seconds at f/22? The way it is phrased in your question is a bit confusing but I think that that's what you are saying.

    If so, I think that you will need to add some neutral density as well, because even with a 4 stop filter, you are looking at 64 seconds if I did the math correctly.

    I have notes on Ilford traditional black and white films having a 1.6x reciprocity factor for long exposures, so let assume it's the same for SFX (your guess is as good as mine, perhaps better!) so this will give you 102.4 seconds @ f/22. So now we have something like 1.7 hours. If you added ND to give an additional 1 stop change, you would be around 3.4 hours, and ND for 2 stops would land you around 6.8 hours- pretty close...

    Please feel free to correct me on any of this - I rarely do exposures longer than a handful of seconds...

    - Randy

    Randy,

    You hit the nail on the head! I was sitting here playing with the calculator, and comming up with the same numbers as you are, but was still confused a bit with how he phrased his question, thank you, you have restored faith in my ability to think!!!

    LOL

    Dave

  10. #10

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    Quote Originally Posted by reellis67
    If so, I think that you will need to add some neutral density as well, because even with a 4 stop filter, you are looking at 64 seconds if I did the math correctly.
    Your response makes more sense than the original posters question.

    If the above is what is being asked the remainder of my comments are directed at Karl. Firstly if you use an SFX (or other IR) filter you'll need to check to ensure that the filter factor for any ND filters you also use applies to IR frequencies as well. Some ND filters only block visible light and let pretty much all the IR frequencies through. Also getting an exact exposure is going to be questionable at the best of times with an IR sensitive emulsion and filter unless you have a meter which properly meters those frequencies. For an indoors estimate it'll be even more of a problem where I couldn't even begin to make a guess as to the amount of IR radiation and hence exposure compensation needed. I don't wish this to sound negative but what I'm suggesting is that if you only have one shot at this it would be worth testing the film, filters and camera/meter in a similar environment beforehand to resolve as much of this as possible.

    Roger.

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