Long exposure times...

Discussion in 'Digital Photography' started by acearchie, Jan 24, 2010.

  1. acearchie macrumors 68040

    acearchie

    Joined:
    Jan 15, 2006
    #1
    For my birthday I got a lomography Diana F+ (basically a simple 120 film camera)

    I have been developing the film myself and decided to play around a little with the pinhole setting (at f150)

    I decided to take a picture in a pub with relatively low light (without a light meter it is hard to put a value on it but the light was similar to this image on google)

    I left the shutter open for almost 40 minutes and there is no exposure at all on the film! I suppose the fact that I was shooting on 120 125iso film may have made a difference but it still seems a long time to me!

    Have I done somethin wrong or did I still under estimate the times needed for pinhole photography? I don't think I did anything wrong in the development as the other pictures I took with the normal aperture settings have come out fine!

    On a side note does anyone know any side by side comparison of what the conditions actually are and how long you would need for shooting pinhole photography?

    Thanks
     
  2. Edge100 macrumors 68000

    Joined:
    May 14, 2002
    Location:
    Where am I???
    #2

    Let's assume the light in the pub was ISO3200, f/1.8, 1/30 (which is not uncommon, in my opinion).

    You were using ISO125 film, so you're 25.6x less sensitive to light than my exposure above, which is equivalent to 4.67 stops (calculated as log2(25.6)). So the equivalent exposure at ISO125 would have been ISO125, f/1.8, 853/1000 seconds (which is (1/30) x 2^4.67).

    f/150 is 6.38 stops slower than f/1.8, so the equivalent exposure at f/150 would have been ISO125, f/150, 71 seconds (853/1000 x 2^6.38).

    A 40min exposure would have given you massive overexposure (over 5 stops).

    So you should have had more than enough light, assuming my estimates of the original light conditions were accurate. In fact, I could have been off by more than 5 stops and you still should have had enough light.

    So I'm not sure why that particular exposure didn't come out, unless you had something blocking the camera for a significant portion of the time.
     
  3. toxic macrumors 68000

    Joined:
    Nov 9, 2008
    #3
    ^ remember there is reciprocity failure with film with exposures longer than 1 second. that still doesn't explain why it's completely black though...overexposure would render it pure white on a print.

    are you looking at the negative or through an enlarger or scanner? assuming that's even negative film... a completely blown out image will be completely black on the negative.

    I'm not sure what the light level is in a pub, but let's say it's EV 4. that corresponds to 4 minutes at f/64 (ISO 100). f/150 is around 2 stops smaller (f/64-f/90-f/125-f/175) after accounting for the extra sensitivity from ISO 125 film, so that would be a 16 minute exposure. if the correction factor is 1.5, that's a 24 minute exposure...but one stop doesn't explain a blank negative.

    if Edge100's estimate of the exposure is correct (ISO 3200, 1/30, f/2 for simplicity), then that would be EV 2 (1s at f/2 at ISO 100), which is another two stops smaller, which puts us at around a 64 min exposure, or 96 min after correction. assuming my math and Wikipedia's tables are correct, anyway. one of us did a calculation wrong...
     
  4. acearchie thread starter macrumors 68040

    acearchie

    Joined:
    Jan 15, 2006
    #4
    Well according to Mr. Pinhole I should have kept the shutter open for about 30-40 mins so I did.

    I also found a diana F+ exposure chart online which states that I should have kept the shutter open for atleast 12minutes.

    Another reading I have read tonight is due to the reciprocity of film it is suggested I leave the shutter open for around 5-6 times longer than suggested! I've also read that with pinhole it is really hard to actually get an over exposed shot due to the very small aperture. Should I do another test where I leave it for say 2hrs? I assumed that with 40mins I would atleast have some exposure of the bright bulbs!

    However there was absolutely nothing on the negative it seems. Completely see through. I have done a bleached out shot before so I know what a totally over exposed shot would look like on the negative!

    However, this time I'm stumped!
     

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