Expo/Disc questions - not sure what to do

Discussion in 'Digital Photography' started by johnpower, Sep 22, 2003.

  1. johnpower

    johnpower Guest

    I have had this thing for a few days now and have tried to understand
    exactly what I need to do to make this work the way it is supposed to.
    I followed the instructions but I am still uncertain about a few
    things. For those who have one and know how to use it properly any
    input would be appreciated.

    I will start with a typical outside shot. I see a rosebush I want to
    photograph with my Canon 10D. The instructions say to first determine
    exposure. OK, so I decide to shoot in the Av Mode, pick 5.6 and get a
    125 Tv. reading. Now I have my exposure, as I understand it.

    I am next told to select manual focus and the manual mode. OK. I
    switch the lens to manual. That's easy enough. But when I go to the
    manual mode on the camera do I then enter to the exposure settings I
    determined to be proper in the preceding step? This is a big question
    I have because the instruction sheet does not say to do this. It just
    says to switch to the manual mode. My common sense tells me that once
    you switched to the manual mode you would dial in the initial exposure
    settings but I just want to know for sure that this is what is done,
    since unless you do, the settings under which the standard is about to
    be taken will not be the previously selected exposure settings (except
    by extreme coincidence)

    OK. I am in my manual mode w/manual focus. Now I am told to compose
    my picture. By this I assume they mean to point my camera back at the
    rosebush, just as I did to determine the exposure settings I wanted to
    use.

    Now I hold the expo/disc in front of the lens, shoot and then use this
    standard as my CWB (which I can easily do by following the camera
    manual's instructions)

    Do I have all this correct? If not, what have I missed.

    And here are a few associated questions:

    1. Assuming the lighting condition do not change, Can I use the
    standard even if I want to change my exposure parameters around i.e.
    maybe open the aperture and raise the Tv or vice versa. Those
    settings would not be my original selected exposure settings with
    which I made the standard

    2. When I have done it this way and I look at the histogram of the
    standard, it is always slightly to the left of the exact middle. I
    have tried retaking the standard with an adjusted exposure
    compensation and it stays in the same place. Do I need to be
    concerned with this?

    3. Do I have to have the camera set to AWB when I shoot the standard
    or can I leave it set to CWB so I can quickly change the standard as
    lighting conditions change without having to switch back to AWB first

    4. When I turn the camera off and then turn it back on and the CWB is
    still the selected setting, is the camera remembering the CWB setting
    from before it was shut off or is it switching back to AWB even
    thought it says CWB is selected.

    Any input is appreciated.

    John H. Power
     
    johnpower, Sep 22, 2003
    #1
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  2. johnpower

    Mick Ruthven Guest

    I've used an ExpoDisc for a couple of months with my G2 (sold the G2 and
    ExpoDisc and got a G3; will get another ExpoDisc for the G3). I find the
    instructions on the site and that come with the ExpoDisc to be confusing. I
    think they were mostly meant for film cameras, but maybe not. Anyway, here's
    how I got great results from it with my G2.

    ExpoDisc for White Balance
    -----------------------------
    - Mostly I'd use it to set a custom white balance and then shoot with that
    CWB for the same light conditions. Essentially the same as setting a CWB
    with a gray card, but usually more convienent. I got to leaving it on as a
    lens cap so it would always be available. (I do wish it had a clip-on
    lens-cap base.)

    - Sometimes I'd also take a shot with the ED on the lens to have a neutral
    gray image to set WB with later (similar to shooting a gray card). And of
    course leave the camera in the same can't-change WB mode while shooting
    (usually the CWB set with the ED). I shoot RAW and mostly use BreezeBrowser
    to convert. With BB I can click on that gray frame (first frame of the batch
    of frames with the same lighting) and tell it to use that WB for all of
    them. The results aren't quite the same as just using the CWB from the ED;
    not sure why.

    - Experiment with pointing the camera/ED at the subject and also going to he
    subject and poiontning it at the light source. Sometimes of course you can't
    go to the subject and point the camera/ED at the light source.

    ExpoDisc for setting exposure
     
    Mick Ruthven, Sep 23, 2003
    #2
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  3. johnpower

    Allegro Guest

    I have an Expo/Disc for my G3 but I could never get consistent WB
    results - it would either be too warm or too cool. I find that Auto
    WB in the camera works best most of the time and as a result have
    practically given up on the disc.
     
    Allegro, Sep 23, 2003
    #3
  4. johnpower

    Mick Ruthven Guest

    Have you asked Diane Wallace for help? I haven't tried it on my new G3 but
    got fine results wtih it on my G2.
     
    Mick Ruthven, Sep 23, 2003
    #4
  5. johnpower

    Paul Cordes Guest

    Yes.
    Or you could just start in Manual mode and adjust untill you get a 0EV
    reading.
    You are of course pointing at the light source. This is called an incident
    light reading.
    And now that the exposure is properly set why not take this same opportunity
    to set the WB.
    After all you should be white balancing off the light source not the
    subject.



    See above the exposdisc behaves like a grey card.....if it's pointed at the
    light source.
    If you put a red rose in front of it you'll get a WB that is definitly way
    into the red with resulting blue pictures.


    Assuming that the lighting does not change then all shots of all subjects
    should be properly exposed.
    You can of course open apature and increase shutter speed by appropiate
    amounts to maintain the exposure.
    Keep in mind that exposure is somewhat subject dependent and you may want to
    either over or underexpose a particular subject depending on the effect you
    desire.

    It means that your camera and the expodisc are not set to the same standard.
    (This is common and not really a fault of either your camera or the
    expodisc. If you bought an external light meter you would have to calibrate
    it to your camera.) You should however be able to adjust the exposure
    (slightly smaller apature or slightly faster shutter and move the histogram
    peak to the right (darker). Don't do this with exposure compensation but
    in Manual mode. By how much you have to move it will determine the
    difference between what the expodisc is telling you is an ideal exposure and
    what the cameras histogram is saying. Remember that difference and dial it
    in for all exposure settings in the future.......ie, trust the camera.
    After all, we have no easy way to adjust the expodisc";^)


    I don't have a 10D.....but I would guess that you want to shoot the standard
    in CWB so that it stays put.
    I believe that AWB sets the WB for each scene based on what it sees in that
    scene and thus will not stay put like the CWB does.......at least that's how
    my cameras behave. By staying put I mean keeping the same WB from scene to
    scene. This turns out to be particularly handy at twilight where the
    landscape goes progressively to the yellow as the sun sets. By keeping the
    WB fixed at an earlier time of the day the photos show the color changes and
    look more like we expect twilight pictures to look. Clear as mud?

    Again I don't have a 10D, but it would be highly unusual for Canon to not
    have the camera remember it's last settings. Mine remembers all its
    settings from the previous session......every setting in every mode, last
    ISO and all.


    Hope that helps.........PC
     
    Paul Cordes, Sep 23, 2003
    #5
  6. johnpower

    Allegro Guest

    I honestly don't think Diane Wallace would even know. I've been
    reading a lot of posts on the dpreview forum and it seems like there
    is no one right way to achieve the best results.
     
    Allegro, Sep 23, 2003
    #6
  7. johnpower

    johnpower Guest

    That would make more sense, since the instructions direct one to
    switch to manual anyhow.
    No. I am pointing at the subject i.e. reflective metering. I don't
    really understand this concept of incident metering, which apparently
    requires that one walk up to the object being shot, turn around and
    meter from the light source. If the sun is behind me, do I point
    directly at the sun? If I am inside in a lighted room do I point at
    the lights? What if you are in a zoo. Do you walk up to the lion
    then turn around and take an incident metering standard?

    Don't the in-camera meters use reflective metering? It would seem so
    because you always point at the subject then shoot.
     
    johnpower, Sep 23, 2003
    #7
  8. johnpower

    Paul Cordes Guest

    With the expodisc you have to point at the source for exposure setting.
    If you point at the subject you will be way underexposed.
    The expodisc transmits 18% of the light that strikes it, just like a grey
    card reflects 18% of the light that strikes it. The meter in the camera
    doesn't expect that you've lost 82% of the light. It expects to see
    approximately 18% of the light reflected from the subject. Not the 18%
    reflected reduced by 82% if you catch the drift.

    Lots of times you don't actually have to walk up to the subject and turn
    around to set the incident light exposure.
    If it's the sun for instance you can probably stand anywhere within a mile
    of the subject and get the same reading. The sun lights you just the same
    as the lion. Point it at the sun, set the exposure, then remove the
    expodisc and see that almost anything you point at is properly exposed.
    Someone inside near a lamp, however, the exposure will be determined by the
    distance of the subject from the lamp. If you and the subject are the same
    distance from the lamp then pointing the expodisc at the lamp will give you
    the proper exposure.

    Remember, you don't have to use the expodisc for every exposure. Sometimes
    it's easier and more accurate to use the cameras meter as it was designed.
    It is however great for WB in almost all situations.

    Clear as mud?
     
    Paul Cordes, Sep 23, 2003
    #8
  9. johnpower

    johnpower Guest

    Thanks for the additional explanation. I have been using it only for
    WB since my exposures using the 10D in camera meter seem to be just
    fine. I will experiment around with the exposure aspect of it

    As far as inside shooting, I can see a problem if you are shooting a
    party and everyone is moving around.
     
    johnpower, Sep 24, 2003
    #9
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