Use of grey card and double exposures.

Discussion in '35mm Cameras' started by Andrew McCall, Feb 18, 2004.

  1. Hi Folks,

    I have college tomorrow and I needed to use another film before I go. I
    took a few pictures of my girlfriend (that might be used for the next
    SI), but I don't think these will turn out OK as I was having to shoot
    below 1/30 of a second due to the lighting and although I was using a
    tripod and shutter release cable, I can't be sure she didn't move.

    This months Practical Photography magazine has a special about still
    life shots you can take indoors, this gave me a few ideas about what to
    use the rest of the film for.

    I set up a mini-studio, consisting of A2 white paper for the floor and
    background, and a movable lamp offering a hard light source to the right
    hand side of the shoot area.

    I took about 12 pictures of an artists lay-doll (wooden man) and a dozen
    apples in different situations - I changed the light, the perspective, the.

    One problem I did find I was having, is when I was using the grey card,
    sometimes I could angle it and get different meter readings, for
    instance I could position it infront of the apples, or position it on
    top of the apples, positioned on top reflected more light, so it changed
    the required settings.

    What do you do in these situations?

    The other thing, I did a double exposure - I wanted to make the lay-doll
    look like that leonadro-de-vinci science man thing. I simply took the
    shot twice without winding the film on, shouldn't there be something
    different I should have done to do this correctly - now some areas of
    the film will have been exposed twice getting twice the amount of light
    needed to correctly expose for the shot.

    No matter what the pictures turn out like, I have to admit, it was
    pretty fun!

    Thanks,

    Andrew McCall
     
    Andrew McCall, Feb 18, 2004
    #1
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  2. Andrew McCall

    Nick Zentena Guest


    If you want to do a double exposure cut each exposure in half. Either a
    one stop faster shutter or close down one f/stop on the lens. You want the
    same total exposure on the film that you would use if you hadn't double
    exposed. This assumes you want both exposures to have equal weight. You can
    vary it. Say you want a very faint ghost image give the model less exposure.
    Bracket. Bracket.

    Nick
     
    Nick Zentena, Feb 18, 2004
    #2
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  3. Andrew McCall

    Alan Browne Guest


    That applies if overlapping a double exp. If you are exposing for an
    object surrounded by black to appear in one area of the frame, and
    another subject (surrounded by black) to appear in another part of the
    frame, then expose each as it requires for a normal exposure...
     
    Alan Browne, Feb 19, 2004
    #3
  4. The best solution is to apply experience.

    Lacking that, I suggest that the gray card should be placed at the
    location of the subject on the same plane as the object being photographed.

    The experience comes in because often there are different subjects in
    different lighting conditions. Experience helps you decide how to meter for
    the results you want.

    Metering based on a formula/gray card will not always be best and will
    result in taking away one of your tools as a photographer (artist).

    Get a good book on lighting, one that includes an explanation of the
    "Zone" System. You don't need to follow the Zone System, but understanding
    it will bring you a long way towards understanding lighting.
     
    Joseph Meehan, Feb 19, 2004
    #4
  5. Andrew McCall wrote:

    The card should be orthogonal to the axis of the lens. That is, it should
    directly face the lens, so that each corner is equidistant from the front
    of the lens. You can be as anal as you like about this, because it does,
    as you observe, make a difference in the reading.

    However, here is where an incident light meter really shines, and if you are
    serious about photography, you should get one. Set up your scene and light
    it. Place the meter as close to the middle of the scene as possible, point
    it (the metering dome) toward the camera, and take a measurement. That'll
    tell you what sort of light the camera is going to see reflected, and the
    surface reflectance of the objects will determine their tonality in the
    image.

    Here's a trick I've used with a gray card: Punch a small hole in each
    corner. Tie a thread into each hole. Cut each fastened thread to the same
    length and then tie them together, making sure the ends are even. The knot
    will be directly over the center of the card and the card will be
    orthogonal to the knot. Tie a length of string to the knot.

    Now you can position the card at the point in the scene you want to measure,
    by fastening the string to the camera such that when the card is in
    position, the slack will be taken from both the string and the threads.
    The card will be orthogonal to the camera. It remains to get a reading,
    however. You can use a meter to take a reflected reading of the card and
    transfer the result to the camera, or you can use another camera for the
    same purpose (I used a reflectance meter before I had an incident meter).

    [optional]
    Remember that the brightness of the light reflected by the objects in the
    scene will not change in relation to the distance of the camera from the
    objects (the inverse square law does not apply here). Incidentally, you
    want to take pictures of a performance in an area where the only lights are
    on stage? You definitely do not need a flash, unless you are very close
    (and you have performer's and presenter's permission to do so). In most
    cases, the performers themselves will be very well lighted already and the
    light reflected from them won't change regardless of how far or near you
    are.
    Answered elsewhere. The exposure needed by the film to capture an image
    remains the same, whether made in single or multiple instances.
    The most important thing you can do is to take whatever steps are necessary
    so that this remains a fun thing to do! Joylessness effectively kills
    photography, I think.

    HTH

    Bill Tallman
     
    William D. Tallman, Feb 19, 2004
    #5
  6. Andrew McCall

    Slingblade Guest

    I haven't done any double exposures in a long time, but seems like the
    rule is to balance the exposures...in other words if you are shooting
    two overlapping scenes, shoot each one at half the exposure you would
    shoot either one as a single exposure. With 3, then you'd do it at
    thirds, etc.

    This only applies to OVERLAPPING exposures. If you were shooting a
    double exposure where half the frame was exposed then later the other
    half, you'd shoot each half at full exposure settings.
     
    Slingblade, Feb 19, 2004
    #6
  7. At times that would be correct, but if the lighting is coming from the
    side and the subject is not flat to the camera then that may not be the best
    idea.

    This all boils down to knowing what you want to measure and then
    figuring out the best way to do it. No one way is always right. (Right
    means the exposure that gets the results you want, not some standard
    exposure.)
    True. One more good tool for the photographer, who knows how to use it.
    110% correct!!!!
     
    Joseph Meehan, Feb 19, 2004
    #7
  8. Andrew McCall

    Alan Browne Guest

    I don't concur. I do do as you say when the light is over the shoulder
    of the photog, however when the light is "side on", this resuls in too
    contasty images and overexposure. Better to angle in "some" of the side
    light to get the exposure pumped down a bit. Slide film, esp.

    If backlit and measuring a subject grey card, I open another stop to
    compensate for contrast loss in the lens (flare).

    eg: there are no hard and fast rules.
    Yep. Also you don't need to be up near the subject ... as long as the
    area where you measure and the area of the subject are similar in local
    reflectors (snow, ashphalt, concrete, buildings, etc.)
    Can you send a picture of this rig Bill?


    Cheers,
    Alan
     
    Alan Browne, Feb 19, 2004
    #8
  9. Let me by saying it a different way. Using a gray card is only a way of
    measuring the lights coming onto the subject. Since the lights make own
    from a number of different directions you need to turn the gray card to face
    that lights these measurements don't really tell you how to set camera they
    tell you what the light is so you can determine how to set the camera.
     
    Joseph Meehan, Feb 19, 2004
    #9
  10. Indeed! When the light is less than about 30 degrees from axis, the grey
    card gets rapidly less reliable, so I found. This is one of the reasons I
    got an incident meter.
    Exactly so. Which is why an understanding of how film records light is a
    needful thing. And of course there are other factors to stir into this
    issue, one of which is surface texture of the subject; how does it reflect
    light? And that's only one of a greater number of such issues than I'm
    likely to have encountered!!!

    And ahead of all that is having some useful idea of the image one wishes to
    produce. Without that, no control is guaranteeable, I think. One can make
    a choice of exposure, based on some arbitrary factor, but one will simply
    get what one gets, and that is that.

    We all get our own peculiar view of these things from the experiences we
    have, and so the only thing we can actually share is the science involved,
    but we can and do offer our notions to each other as suggestions for areas
    and directions to explore. It's difficult to summarily evaluate such
    things as we would do with matters of fact, so I guess we really just have
    to try things out and come to our own conclusions.

    Early on in my learning about photograph (still a kid with Dad's darkroom
    still extant, albeit not always available), I ran across the notion of
    texture as a part of the Zone System idea. IIRC, the subject was a white
    wash cloth pinned to a white wall. Metering on the wash cloth gave an
    exposure to record it as 18% grey, or Zone 5. Definitely not white, but
    fully textured. As I varied the exposure, the texture started to
    disappear, and I discovered that more than one stop either way
    significantly reduced the detail of the texture.

    From this, I got that Zone's 4, 5, and 6 were where I had to place surfaces
    that I really wanted to retain the detail, and that there was a noticeable
    difference between the detail loss in Zones 2 and 3, and Zones 7 and 8.

    So I got that the idea of how bright a thing might appear wasn't the real
    determinant of how bright I wanted to record it on film, that instead it
    was the amount of surface detail (texture) that made that determination.
    From there, one can print to place texture wherever one wants in terms of
    tonality, within limits.

    I can't remember where, or whether, I've ever read about this recently,
    although I'm sure that Adam's books discuss the issue. And I don't know
    how this approach squares with those used by any of you guys, but that's
    (some of) my take on lighting and that's how I got that take in the first
    place.

    In any case, Andrew, that's something you might think about, though I'm not
    recommending the approach (lest I be seen leading you into photographic
    practices not generally recommended... LOL!!!).

    Enjoy!!

    Bill Tallman
     
    William D. Tallman, Feb 19, 2004
    #10
  11. Andrew McCall

    Bob Hickey Guest

    Try to think of the light having a range, instead of "The One True
    Exposure". In other words, if you place the grey card at the subject, and
    turn it to the brightest and dimmest reading, you might get 1/30s and 1/2s.
    That would make 1/8s a good starting point. Moving the light closer in by
    half, might give you 1/125s and 1/2s. Too contrasty. If you double the
    distance, you might get 1/8s and 1s. Too flat. There are all kinds of
    combinations, but settling on one, just makes photography dull. Getting
    perfectly repeatably results isn't hard, just get a spot meter. Enjoying it
    is the whole trick. Bob Hickey
     
    Bob Hickey, Feb 19, 2004
    #11
  12. Yep, side on is a bad situation for a grey card in any case. "Angling in",
    I think, just compounds the problem, because there's no way of determining
    how much to angle (so far as I know, anyway). I've other criteria for
    lighting than just observed tonality, but for me, I want to know what the
    light is at that distance from the source, and then make my decisions from
    there.

    One way of doing that, of course, is to meter the card placed directly
    orthogonal to the source. That gives you a way of determining the diffused
    reflectance from subject surfaces facing the light. That's useful if one
    is using a fill from the other side, because it's independent of the fill.
    If you meter on a grey card directly, ie, no backlighting hits the meter,
    the exposure will be correct for the grey card, but you get what you get
    from the flare in any case. Like all of us, I've had difficulties with
    this situation and try to avoid it unless I've a notion of what I want to
    do with it. In the wild, one doesn't have that luxury, so the 1/1.5 stop
    addition makes the best of what can be a bad situation. Sometimes one
    wants to preserve some detail in the backlit area (spray, dust, etc) and
    I've found that one stop will often do that. Sometimes one just wants the
    halo, and a stop and a half will tend to get that.

    What's really interesting to do is to go out, take an incident reading, set
    the camera and just shoot, presuming that the light is what it is. Dunno
    what happens for slide shooters, but more often than not negs come up just
    fine, and with no worries about compensating for metering.
    Yep. There are some rules of thumb for studio work, I gather, and I suppose
    that instead of rules, one might simply say suggestions.
    Yeah, and this is an extra added complication. Light can be additive, of
    course, which is why scenes with added or subtracted reflectance need to be
    metered directly.

    Hmmm.... don't have one at the moment. The idea is fairly simple though.
    Probably want to have the threads at least the length of the diagonal of
    the card after they are tied, but probably not more than twice that length.
    The idea is that if one let the card dangle, it would be level (orthogonal
    to the center of the earth) and the knot would be directly over the center
    of the card.

    Does that make sense?

    Bill Tallman
     
    William D. Tallman, Feb 19, 2004
    #12
  13. Exactly so!

    Bill Tallman
     
    William D. Tallman, Feb 19, 2004
    #13
  14. Andrew McCall

    Alan Browne Guest

    and once you're there, measuring the light from the sides by turning the
    card to max glow, you know how much "off mid tone" you're going to get.
    From there, you have a good idea how much to close down to make that
    acceptable while not losing too much on the subject.
     
    Alan Browne, Feb 20, 2004
    #14
  15. Well, I learnt a thing or two in this thread. I've never used a gray card
    that way, but it makes eminent sense.

    I noted Alan's use of the term "max glow": I wonder if that is the
    brightest point.

    My knowledge of photography is extensive but quite spotty, not unlike many,
    I expect. Dunno how I missed this, or simply have forgotten it, but in any
    case, it's a trick now in my bag!!

    Thanks to Bob and Alan for this!

    Bill Tallman
     
    William D. Tallman, Feb 20, 2004
    #15
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