Canon Digital Rebel metering in low-light

Discussion in 'Digital Photography' started by Siddhartha Jain, Jan 10, 2005.

  1. Hi,

    Take a look at these shots
    http://gallery129375.fotopic.net/c395008.html
    (WARNING: The originals are 2+MB each)

    When I was setting the camera for these shots, the indicator on the EV
    scale had gone below -2EV and so was blinking. I would say the
    exposures were -3EV to -4EV from the camera recommended "0" EV.

    Everyone in my office who looked at the photos liked them so I am
    assuming the exposure is right. The question is that if the exposure is
    right then how come the camera meter was WAY off?
    Canon 300D
    Canon EF-S 18-55mm f/3.5-5.6

    - Siddhartha
     
    Siddhartha Jain, Jan 10, 2005
    #1
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  2. Siddhartha Jain

    Guest

    The camera metering assumes that the average illumination is 18% (or
    13% depending...), so when you take an image of a large swath of dark
    stuff the camera metering will try to make the dark stuff (well)
    darkish (18%). This is about 3 stops from perfectly exposed.

    Conversely, when you take an image of the moon at night, the metering
    thinks the average illumination is the sky and will overexpose the moon
    by about 3 F/stops.

    White cats in a snow storm and black cats on a black bed spread have
    similar problems.

    The metering does not and can not understand the image, and that is
    what EC is for. You, the photographer, need to understand what the
    metering does (e.g. how it thinks), and what kind of circumstances you
    should wrest control over the camera metering.
     
    , Jan 10, 2005
    #2
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  3. wrote:
    > The camera metering assumes that the average illumination is 18% (or
    > 13% depending...), so when you take an image of a large swath of dark
    > stuff the camera metering will try to make the dark stuff (well)
    > darkish (18%). This is about 3 stops from perfectly exposed.
    >


    Got it. I assumed that as soon as I switch to manual mode the metering
    goes to partial. But it doesn't work that way. One has to press the AE
    button to switch from centre weighted to partial in the "M" mode.
    My bad, should've read the manual more closely :)

    - Siddhartha
     
    Siddhartha Jain, Jan 10, 2005
    #3
  4. Siddhartha Jain

    Matt Ion Guest

    Todd H. wrote:

    > Also with long exposures, there's this bit about reciprocity failure
    > that comes into play as I recall.


    "Reciprocity failure" is the tendency of color films to shift color over
    long exposures; the real problem with it is that it's inconsistant and
    largely unpredictable and varies from one brand and formulation of film
    to the next. It DOES NOT affect digital photos (see
    http://www.pbase.com/bret/image/34152731 and note the exposure settings).
     
    Matt Ion, Jan 10, 2005
    #4
  5. Todd H. wrote:
    >
    > I'd be curious if your photos would look punchier if they were

    exposed
    > even longer, or at higher ISO's.


    I kept the aperture at f/8 coz I figured (from some previous subjective
    tests) that this is where the lens would be at its sharpest. Kep the
    ISO at 100 coz didn't want any noise. Hmmm ... But I could've
    definitely set to BULB and taken longer exposures. Or bumped up the ISO
    to 400 or 800.
    Anyways, thanks. I'll keep all that in mind in future :)

    - Siddhartha
     
    Siddhartha Jain, Jan 10, 2005
    #5
  6. Siddhartha Jain

    Todd H. Guest

    "Siddhartha Jain" <> writes:

    > Hi,
    >
    > Take a look at these shots
    > http://gallery129375.fotopic.net/c395008.html
    > (WARNING: The originals are 2+MB each)
    >
    > When I was setting the camera for these shots, the indicator on the EV
    > scale had gone below -2EV and so was blinking. I would say the
    > exposures were -3EV to -4EV from the camera recommended "0" EV.
    >
    > Everyone in my office who looked at the photos liked them so I am
    > assuming the exposure is right. The question is that if the exposure is
    > right then how come the camera meter was WAY off?
    > Canon 300D
    > Canon EF-S 18-55mm f/3.5-5.6


    Camera meters aren't all that smart. They evaluate a scene, and more
    or less want the result to be middle gray, and in digital perhaps
    they're doing math to minimize the number of pure white (all 1's)
    pixels. If you shoot a black cat in a coal mine, a proper exposure
    will be a few stops below middle gray. If you shot a white cat in a
    snow storm, your exposure will have to be a few stops over middle gray
    to look accurate.

    Your shots are a nighttime scene, and are very dark--and I'd agree
    with your camer that they are several stops below middle gray.
    Techincally, they are somewhat lacking in contrast and could stand to
    punched up a bit, and I think they might benefit from having been
    exposed longer. I don't see any areas that are at risk of becoming
    overexposed anytime soon.

    Also with long exposures, there's this bit about reciprocity failure
    that comes into play as I recall. I don't know enough about the
    subject to expound upon it at great length though, but what I remember
    of it tells me to not expect any metering to be terribly accurate when
    you get into 15 and 30 second exposures. "Bracket like hell--those
    buildings aren't moving away anytime soon" is the advice I tend to
    follow to get a good one.

    I'd be curious if your photos would look punchier if they were exposed
    even longer, or at higher ISO's.

    Best Regards,
    --
    Todd H.
    http://www.toddh.net/
     
    Todd H., Jan 10, 2005
    #6
  7. Siddhartha Jain

    Chris Brown Guest

    In article <>,
    Siddhartha Jain <> wrote:
    >
    >Everyone in my office who looked at the photos liked them so I am
    >assuming the exposure is right. The question is that if the exposure is
    >right then how come the camera meter was WAY off?


    They're night shots, dominated by dark skies. Assuming you were using
    evaluative metering, it never really stood a chance. Try partial on the
    buildings, with maybe -1 EV for this sort of thing, and experiment around
    there. You should find you get better results.
     
    Chris Brown, Jan 10, 2005
    #7
  8. On Mon, 10 Jan 2005 17:05:44 +0000, Siddhartha Jain wrote:

    > Hi,
    >
    > Take a look at these shots
    > http://gallery129375.fotopic.net/c395008.html (WARNING: The originals
    > are 2+MB each)
    >
    > When I was setting the camera for these shots, the indicator on the EV
    > scale had gone below -2EV and so was blinking. I would say the exposures
    > were -3EV to -4EV from the camera recommended "0" EV.
    >
    > Everyone in my office who looked at the photos liked them so I am
    > assuming the exposure is right. The question is that if the exposure is
    > right then how come the camera meter was WAY off? Canon 300D Canon EF-S
    > 18-55mm f/3.5-5.6
    >

    They are pretty good shots - but of course beauty is in the eye of the
    beholder. Shots 1 & 2 are technically underexposed but the shot number 3
    is fine.

    When taking shots of illuminated buildings, the best way I found is to use
    a spot meter (partial metering of Digital Rebel will do). Select the area
    which you want to be properly exposed. Take a reading from that area alone
    and then set the exposure manually. Quite often a bit of overexposure, by
    half to a stop, improves the atmosphere, specially if you are taking the
    maximally illuminated area as your target (that is often a natural
    tendency). Alternatively, take several spot (partial) readings from two or
    three interesting areas and then use the middle one.

    --

    Gautam Majumdar

    Please send e-mails to
     
    Gautam Majumdar, Jan 10, 2005
    #8
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