Really low light metering, is it possible?

Discussion in 'Exposure Discussion' started by hammy, Jan 31, 2007.

  1. hammy

    hammy Member

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    The other night I was in the mountains and came outside to my car and found a nice moonlit scene.


    What are the capabilities of light metering? I know with my built in meters on my 35mm cameras, it will only meter as low as 1/4 sec.

    So, are there any meters that can meter night scenes?
     
  2. JBrunner

    JBrunner Moderator Staff Member Moderator

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    Spectra Candella, but there are some others that read dimmer...Somebody will tell us what they are in just a few minutes.....
     
  3. Ray Heath

    Ray Heath Member

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    g'day hammy
    it is possible to use the camera's meter by changing the ISO to it's highest setting then doing the math to get back to the actual ISO of the film in use

    don't forget reciprocity failure

    err on the side of over exposure
     
  4. Helen B

    Helen B Member

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    A Gossen Profisix (Luna-Pro-something outside Europe) will meter down to Ev -8 at ISO 100. That's about an hour at f/4 before taking reciprocity failure into account. A Sekonic L-508 with a Minolta Booster II attached is two stops more sensitive than that. Whether you really need to meter down to that level is a different matter. I never bothered in full moonlight: Kodachrome 64 at f/4 for ten minutes, or so.

    Ray, does changing the film speed setting on a meter make it any more sensitive?

    Best,
    Helen
     
  5. Matthew Gorringe

    Matthew Gorringe Member

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    It's good to know there are some meters available that can do it but I haven't bothered for night time stuff.

    Similarly to Helen I've just picked one film, one F stop and the experimented with time until there was good density on the negative. For me it's Delta 400 in Xtol 1:2, f16, and between 8 and 12 minutes for a scene with good artificial light. I think 20min+ might be good for moonlight.
     
  6. Sirius Glass

    Sirius Glass Subscriber

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    1) See Exposure Forum "Lunar exposure time @ f10/ISO 100" my comments.

    2) See FotoSharp
    "Day and Night Exposure Guide"

    FotoSharp
    17837 1st Ave S, #1
    Seattle, WA 98148

    800 361 8341

    www.FotoSharp.com

    Using this calculator for ASA 100
    Snow or sea lit by full moon - 1 minute f/4
    Landscape by full moon - 1 minute f/2.8
    Landscape by half moon; Closeup lit by full moon - 4 minutes f/4 or i minute f/2

    This will cost you much less money than a meter.

    Steve
     
  7. Woolliscroft

    Woolliscroft Member

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    The Olympus OM-2 and 4 will take exposures up to 2 minutes on auto and seem to do it fairly accurately if you bias to allow for reciprocity failure. Sadly they only go down to 1 sec on manual.

    David
     
  8. DougGrosjean

    DougGrosjean Member

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    Google on the "Ultimate Exposure Calculator".

    It's a spreadsheet with exposures far down into the negative EV numbers. I think the lowest it goes is a summer night scene lit only by starlight. Which is different from a winter scene lit by starlight reflecting on snow... Which is different from a moonlit night scene, etc.

    I've shot as far / slow as a moonlit winter scene, and found the UEC to be accurate.
     
  9. mawz

    mawz Member

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    The Pentax LX will also meter down to EV -6.5 in Auto (aperture priority) mode.
     
  10. grahamp

    grahamp Subscriber

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    You can boost the effective sensitivity of a meter by almost 3 stops by metering a white card in the same way you would use a grey card, and applying a correction.

    Though I would do some tests on any meter not designed for low light work. linearity tends to suffer at the extremes.
     
  11. Kirk Keyes

    Kirk Keyes Member

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    Helen - I've got a Booster II for my Minolta FLashmeter IV. Are you saying to simply point the booster at the scene and take a reading? Which attachment would you recommend? ANd I seem to remember there is a dial on the booster - where should that be set?

    Kirk
     
  12. jd callow

    jd callow Moderator Staff Member Moderator

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    Luna Pro SBC and F as well as the original which I believe is simply called the Luna Pro, are the meters I've used with great success.
     
  13. Helen B

    Helen B Member

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    Kirk,

    Sorry to take so long to reply, but I wanted to put the gear together to demonstrate. Here's how it works with the L-508:

    [​IMG]

    The dial on the booster is set all the way round to H, then you compare the reading of a grey card or something similarly even with a spot reading taken without the booster. Adjust the meter's exposure compensation until the reading with the booster matches the reading without. My L-508 needs a compensation setting of -7 stops.

    As you can see, the meter is reading Ev -8.6 at ISO 100, or f/2 and a half at 1800 seconds. That reading was taken inside a dark room with barely enough light to see.

    For 'normal' use you adjust the booster's dial to get the readings the same, instead of adjusting the meter compensation.

    Best,
    Helen
     
  14. Greg Campbell

    Greg Campbell Member

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    Here's the ultimate (consumer) low-level meter.

    http://unihedron.com/projects/darksky/

    Is spits out magnitude per square arc second. The unit is a bit unwieldy, but still represents a surface brightness level. By installing an appropriate mask over the sensor, and calibrating the resultant values, you could make an exquisitely sensitive spot meter. I've been pining for one for some time, and hope to have one by this summer's monsoon / lightning season.

    -Greg
     
  15. Helen B

    Helen B Member

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    If my quick and dirty maths is correct, that meter is sensitive to about Ev -9 at ISO 100, assuming that 22 magnitudes/square arcsecond is the lower limit of sensitivity. It might be more sensitive than that, but I couldn't find any other value on the website.

    Best,
    Helen
     
  16. Lee L

    Lee L Member

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    It also reads as a reflectance meter covering about an 80 degree cone (1.532 steradians). A wise choice for its intended purpose, but not a replacement for your one degree spot meter. :smile:

    I'd think you'd need both a mask and optics, plus a properly aligned viewfinder to make it into a spotmeter. I'd also think that masking it down to that degree could possibly put it below the sensitivity of some other commercial meters like the LunaPros. But do report back here on your mods for the curious among us.

    Lee
     
  17. Kirk Keyes

    Kirk Keyes Member

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    Thanks Helen!

    I'm still hoping for that filter/spectra calc program/spreadsheet you mentioned a while back...
     
  18. ben-s

    ben-s Member

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    FWIW, I usually expose moonlit landscape scenes at ISO100, f/8 for 4 mins or thereabouts.
    I can't post any examples because the only ones I have on hand are made of pixels, but this exposure seems to work well for me.
     
  19. benjiboy

    benjiboy Subscriber

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    Take Care

    If you make long exposures on cameras with electronic shutters make sure you have a few spare batteries with you, because the cameras use them to power an electro- magnate to hold the shutter open, even for time exposures.
     
  20. Lee L

    Lee L Member

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    Some well-designed cameras with electronic shutters have a mechanical B or T setting. Both my electronic shutter SLRs have this feature, as well as one mechanical shutter speed at flash synch, and the one with red LED indicators bleeds into the film compartment on really long exposures, so I remove the batteries for exposures of more than a few minutes with that body. This is not an uncommon problem among cameras with LEDs in the finder.

    Lee
     
  21. DrPablo

    DrPablo Member

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    I know from experience that my Sekonic L-358 will not offer readings at low ISO settings, but if you alter the ISO it will provide a reading. It's probably not that it's any more sensitive, but that it doesn't offer exposure times longer than 30 minutes, so it will opt out of any ISO that requires a longer exposure than that.

    This meter, while wonderful in the daylight, will only give reliable spot or incident readings down to Ev 5 and reliable reflective readings down to Ev 2 or 3.