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  1. #21

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    Quote Originally Posted by RH Designs View Post
    Anyone who's tried to match an inkjet print to the screen image without using a fully colour managed workflow will know what I mean! Using a glossy paper for a grey card makes matters worse because of reflections etc.

    Best to use your hand or a commercially produced grey card. Better still, a spot meter.
    I'm not sure why this is being made so difficult. You print with your best guess and paper settings. You test. If not on the money, you adjust. More saturation or less. Save those settings. You can also print to fiber. No need for color managed workflows or similar.

    One could just as well take a piece of white paper, spray black paint on it in a mottled fashion, and at an appropriate distance, have an 18% reflectance. No color management or workflow!

    I specifically stated that a) I could only get the Delta card locally (and the dealer was surprised to see that he had a set!) and, 2) the surface is lumpy and shiny, which I can't believe doesn't sometimes impact a reading. And 3), there you are for your monitor, regardless of anything else.

  2. #22

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    Cameras use 12% grey

    To throw a spanner (wrench) in the works, I read an article that camera's are calibrated at 12% gray.

    http://www.bythom.com/graycards.htm

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  3. #23
    Steve Smith's Avatar
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    Quote Originally Posted by RH Designs View Post
    The problem is - how black is the black and how white the white? This would work with perfect 0% and 100% black and white respectively, but not otherwise.
    I think you are right but I also think that a correctly proportioned white/black pattern would be easier to achieve than a 18% grey with an inkjet print.

    But I wouldn't suggest that either was an ideal solution.

    I think metering the palm of the hand and adding an extra stop (or using the C position on a Weston meter) is a good solution as you are not likely to forget to bring your hand!



    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  4. #24

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    Quote Originally Posted by ooze View Post
    Is that with a sunburn or without?

    I mean, after driving for a whole day in high summer the back of my hand easily goes down to ZoneIV if not darker

    If I have no other good reference I usually measure off the palm of my hand and open up by ~1 stop. The palm tends to stay the same shade.
    I think what you are getting at is the idea of measuring parts of the body which do not see sunlight very much and thus remain at a constant value. Perhaps some of you have already guessed where this post is going. In the field, I usually wear very loose pants and carry a mirror.

    Ok, just kidding.

  5. #25

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    Man, just when I think I can tie my shoes!

    Quote Originally Posted by Robint View Post
    To throw a spanner (wrench) in the works, I read an article that camera's are calibrated at 12% gray.

    http://www.bythom.com/graycards.htm

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    From the above, "someone had shot a picture of a gray card, and then remarked that his meter must be off, since the histogram that the camera generated showed the peak of values to the left of center."

    I noticed the same thing! I figgered it was just my Dimage program or some peculiarity that I didn't understand.

    After reading that, I guess it only confirms that trying to expose to the .001 proper EV is a total waste of time. Second, run your own tests!

    Sunny sixteen it is, after all this technology.

  6. #26

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    A kodak 18% grey is the middle of what exactly? When you can fully explain that and can quote the angles it requires and can implement those angles before metering it, then you will realise that a grey card is as much use as a concrete parachute and do what all sensible people do and throw it away.

  7. #27

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    Quote Originally Posted by Robint View Post
    To throw a spanner (wrench) in the works, I read an article that camera's are calibrated at 12% gray.

    http://www.bythom.com/graycards.htm

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    That 12% is what is called a K factor and its what camera and meter manufacturers use to calibrate their meter to the mid point of the film characteristic curve. That begs a few questions such as which film?
    For example, a colour neg film or chrome/transparency film. There is abig difference between them.
    I don't know what the K factor for my contax camera is but I have heard many times that the in camera meter is calibrated for transparency films. But then not all transparency films have the same dynamic range. And nor do all negative films. That is one of the major reasons why you should do your own film testing and exposure calibration.
    My minolta spot Meter F uses a K factor of 14. Not that that is really worth knowing because again, the particular film dictates what the exposure should be and not the meter. So calibration is required.

  8. #28
    Christopher Walrath's Avatar
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    You ought to be able to make one in MSPaint. Custom colors, pick a neutral and adjust it to the midpoint of 255 and 0 (127) and fill a frame and then print it.
    Thank you.
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  9. #29
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    Quote Originally Posted by rob champagne View Post
    A kodak 18% grey is the middle of what exactly?
    The value of "18%" was/ has been selected as an ARBITRARY determination of "mid-color" and density of the "average" scene. By whom and just what the parameters of selection were, I have no idea, and I wonder if anyone else does.
    "Precise and/ or exact"? I doubt it - more like "better than nothing".
    When you can fully explain that and can quote the angles it requires and can implement those angles before metering it, then you will realise that a grey card is as much use as a concrete parachute and do what all sensible people do and throw it away.
    What is with this "angles" business? In use one substitutes the gray card for part of the subject, in the same light, and the exposure is set. Then if 95% of the light is reflected from a white subject surface, it will be recorded as 95% white, not 18% gray. The meter itself doe not know whether the subject is supposed to reflect 5%, 18%, 95% or whatever - it will process the information to produce 18% gray (or 12% - or 13.5% - I don't think there is a great deal of difference)..

    A "concrete parachute?" Certainly not perfect - but as stated before, a whole lot better than nothing.
    Carpe erratum!!

    Ed Sukach, FFP.

  10. #30

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    Quote Originally Posted by Ed Sukach View Post
    What is with this "angles" business? In use one substitutes the gray card for part of the subject, in the same light, and the exposure is set.
    Ever bothered to read the instructions that come with a genuine kodak grey card? Obviously not. here's the relevant paragraph:

    “Position the grey card in front of and as close to the subject as possible. Aim the surface of the gray card toward a point one third of the compound angle between your camera and the main light. For example, if the main light is located 30 degrees to the side and 45 degrees up from the camera to subject axis, aim the card 10 degrees to the side and 15 degrees up.”

    This means you need to buy a sextant to use a grey card accurately.
    Don't take my word for it. Just point a light meter at a grey card or any card for that matter, and change its angle around and watch your light meter change its reading. And see its apparent colour change depending on its angle.

    So what's the point of a grey card. You have no idea what percentage or colour it is unless its set perfectly accurately and even then who says 18% is the mid point of your subject? I bet it isn't.

    Of course if you always point it at the camera then at least its consistently wrong and no doubt you have calibrated your methods to take that into consideration without even realising.[edit]And unless the lighting direction is always exactly the same then it's NOT a consistent reference is it.[/edit]

    Why not just take a light reading of the actual light falling on the subject and tear your grey card up. It's simply making things more inaccurate and patently not required when you have a light meter to do the job for you. And AA said himself that if the whole subject is not in the same light, then a grey card is useless. Since anything in shadow is not in the same light as the rest of the image, then that accounts for about 99.9999999% of all images which AA said a grey card is not suitable for. You will have to read the Negative properly next time so that you don't miss that "Very Important" sentence.
    [edit]Just point your incident meter directly at the light source which is illuminating what is facing the camera and you will get highly accurate and consistent light readings. The tones rendered will fall where they fall but if you are consistent with your metering then you will know very quickly whether to adjust exposure or development from the reading[/edit]

    Rant over. Normal service resumed... Oh that was normal. Well never mind.
    Last edited by rob champagne; 03-13-2008 at 12:06 AM. Click to view previous post history.

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