Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,530   Posts: 1,543,972   Online: 1081
      
Page 16 of 23 FirstFirst ... 610111213141516171819202122 ... LastLast
Results 151 to 160 of 228
  1. #151
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,278
    Images
    46
    Suppose you dim the light with filters, to rule out the aperture shape/area change that might shape how large the internal reflections are.

    So put a clear gelatin filter for the first shot and a 2.1 ND filter for the second shot. That will give two shots that differ only in intensity x time.

    Here I believe you would find flare the same in both cases.

  2. #152

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,730
    Really? Even camera flare (light bouncing around in the camera even with flat black surfaces, light reflecting off the emulsion adding to this)?

  3. #153
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Quote Originally Posted by Michael R 1974 View Post
    In my mind I'm thinking higher intensity causes more reflection off various surfaces (including the emulsion itself), so flare should increase even though the light is present for less time compared with the second exposure. Not sure. And it is difficult to test in practice due to possible shutter speed inaccuracies.
    Michael, the higher intensity will of course create a higher reflective light level. But as they are part of the target, which is a uniform luminance source, it has nothing to effect. Think of flare as a bleeding of light from the brighter scene elements (average of 3 percent of the greatest scene luminance) adding to the darker exposure values. If the target is the only luminance value, what is it going to bleed into and how can it add to itself?

    Just reading the list of meter modifications (various filters, baffling) was depressing enough
    It's enough to make a person question whether knowable testing is possible with such devices.

    I'll try to re-read the exposure meter part of Henry's book so the material will be fresh for both of us. One thing to remember is sometimes the variables can create an accumulative effect and sometimes they can cancel each other out. If you have a chance, you might want to check out the thread Is the K-factor Relevant to me or should I Cancel it Out? Around the third page, I begin posting attachments outlining exposure including exposure meters and the variables in the equation for determining K.
    Last edited by Stephen Benskin; 01-25-2013 at 09:31 PM. Click to view previous post history.

  4. #154
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,278
    Images
    46
    Quote Originally Posted by Michael R 1974 View Post
    Really? Even camera flare (light bouncing around in the camera even with flat black surfaces, light reflecting off the emulsion adding to this)?
    Right. The light would bounce around just the same, only it would be proportionally dimmer.

    Now I use Zones loosely in this discussion. When I test film it's with a sensitometer. Then I work in Zones as I study my graphs because I find it easy to get my head around. I imagine where the different Zones will fall on the curve. I look at Zone I and lift that point to the Y-axis coordinate corresponding to about Zone II (I say about, because I look 0.4 LogE to the right). The difference is a certain number of Meter-Candle-Seconds which I take and "add" to each of the coordinates of my step wedge. Flare's impact quickly tapers off. But this is how I take a sensitometer test and make it agree with light meter marked with Zone System grays.

    In a sense I call the camera test you describe as a no-flare test. Even though the camera introduces flare. I say no-flare because the amount of flare at Zone V exposure is about what would take Zone I up to Zone II. BUT, in a camera test you stop down four stops and it no longer brings you from Zone I to Zone II. Now it only takes Zone -III to Zone -II (which is to say 'nada').

  5. #155
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,278
    Images
    46
    Quote Originally Posted by Michael R 1974 View Post
    The whole meter issue really bothers me. ... Just reading the list of meter modifications (various filters, baffling) was depressing enough.
    Trust one good meter and leave it at that.

    I could wish for a spectrophotometric meter that could be programmed for my favorite film and which also could interpret the effect of black and white contrast filters to predict the Zone System placement. Totally possible with current technology. But that would reduce metering to a "point and shoot" frame of mind, which takes some of the fun (and all the participation) out of it.

    Lately, as I experiment with my Weston Master II and Zone System sticker, I once again "walk in the footsteps" of Ansel Adams. I can walk up to a gray wall, set the meter to V. Point at sky and see needle go up to IX. Point at a green plant and stop to think... The Master II selenium cell is making the plant go to VI but I know it is really still V. Finally learning these tricks that used to drive him and Fred Picker to make these modified meters. But they always dealt with it until the Zone VI modified meter came out.

  6. #156

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,730
    Ok, in the flare example the more I think about what Stephen said I think we can at least remove reflection off the emulsion. So we've removed that element, and removed the diaphragm as a variable by using and ND filter. So the possibility we're left with is simple camera flare. Here is where I'm still unsure - because assuming I don't mask the lens to an image rectangle with projection limited to the emulsion area, the image circle is larger than the film, so indeed additional extraneous light could bounce off surfaces in the mirror box, onto the film and cause increased exposure. Is this reasoning correct?

    If that is correct, the question again would be, given the equivalent image forming units of light in the two exposures (1/60 @ f/2, 1s @ f22), would there be a difference in film density for this relatively low density (actual density or "Zone" not really critical, as long as the net density above FB+f is quite low - say somewhere around 0.1-0.2 above FB+f).

  7. #157
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Quote Originally Posted by Michael R 1974 View Post
    Ok, in the flare example the more I think about what Stephen said I think we can at least remove reflection off the emulsion. So we've removed that element, and removed the diaphragm as a variable by using and ND filter. So the possibility we're left with is simple camera flare. Here is where I'm still unsure - because assuming I don't mask the lens to an image rectangle with projection limited to the emulsion area, the image circle is larger than the film, so indeed additional extraneous light could bounce off surfaces in the mirror box, onto the film and cause increased exposure. Is this reasoning correct?
    I can't speak with any certainty to camera design and all the elements that contribute to flare, but generally what you are describing are things that could add to the level of flare.
    If that is correct, the question again would be, given the equivalent image forming units of light in the two exposures (1/60 @ f/2, 1s @ f22), would there be a difference in film density for this relatively low density (actual density or "Zone" not really critical, as long as the net density above FB+f is quite low - say somewhere around 0.1-0.2 above FB+f).
    The flare factor is calculated by how much the shadow exposure is affected. I believe the standard practice is to use the shadow exposure 4 1/3 stops down from the meter exposure point of a statistically average scene luminance range. A one stop filter factor means flare doubles the shadow exposure 4 1/3 stops below the metered exposure. If the luminance range is shorter than the statistically average and the shadow exposure doesn't reach down 4 1/3 stops, then there's nothing there to add exposure to. Where the shorter luminance range shadow falls in this example will not experience a doubling of exposure.

    Within the same optical system, the only way to change the flare factor is by a change in the luminance range or change in the portion of dark and light tones in the scene and how they are distributed. Adding or reducing the camera exposure should just move back and forth along the x-axis.

    Currently reading about K in Henry's book. If I didn't already understand what the K-factor is, I still wouldn't know after reading that section. Another example of how he just might not be into theory. Still have the testing for K to get through.

  8. #158

    Join Date
    Feb 2010
    Location
    Montreal, Canada
    Shooter
    Multi Format
    Posts
    4,730
    Quote Originally Posted by Stephen Benskin View Post
    A one stop filter factor means flare doubles the shadow exposure 4 1/3 stops below the metered exposure. If the luminance range is shorter than the statistically average and the shadow exposure doesn't reach down 4 1/3 stops, then there's nothing there to add exposure to. Where the shorter luminance range shadow falls in this example will not experience a doubling of exposure.
    I'm not following. Did you mean to say a one stop flare factor? Let's assume the two exposures I listed are both 4 1/3 stops below metered and that the film density under zero flare conditions would arbitrarily be 0.20 above FB+f in either case. In the first exposure, the intensity of light entering the camera is high, and so some of this light (from the portion of the image circle beyond the borders of the emulsion) might bounce around, eventually bouncing onto the film and adding some additional exposure. At least I think it might. Maybe the actual film density ends up being 0.23 above FB+f. In the second exposure, a much lower intensity of light enters the camera, but the shutter is open for longer. Would we still expect a density of 0.23? Or would we actually get the zero flare density of 0.20 because the light intensity is not high enough to cause significant reflections in the camera - even though the film is exposed for longer.

    Perhaps there is no definite answer. Here's another way to think about the same example. You take a picture of a bright, uniform, featureless mid day sky and expose it to produce an expected net film D of 0.20. In the evening you take a picture of a middle grey, uniform, featureless evening sky and expose it to produce a net film D of 0.20 (so obviously this would be a significantly longer exposure than the picture of the mid day sky). Assume some camera flare in the first exposure leads to an actual net film D of 0.23. Would that occur in the second example too, even though the intensity of light entering the camera is lower? I'm thinking there would be less, or zero flare in the second exposure. Not sure.

    Keep in mind this question concerns an in-camera film test with as little flare as possible (aside from some degree of lens flare which cannot be totally eliminated). The aim is to use a brightly lit white card for the entire series of exposures. In actuality, the lens is masked to restrict the projected image to within the borders of the emulsion. In other words, there should be no camera flare. But even though I would be using this mask anyway as an extra precaution, I'm wondering if it is necessary. So my example above would be the equivalent of not masking the lens.

    Sorry again for repeating myself. I just want to make sure I really understand this.

    Regarding the K-Factor discussion in Henry's book, as it happens I re-read that very section today, and I came away just as little understanding as when I first read the book. I wish he had started by explaining what the K-Factor actually is before getting into the ranges, calculations, standards etc. I still don't get what the K-Factor is. The only thing I think I understand is that it is not what Adams said it was. When you read Adams you come away thinking it is just a safety factor built into the meter.

  9. #159
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Quote Originally Posted by Michael R 1974 View Post
    I'm not following. Did you mean to say a one stop flare factor? Let's assume the two exposures I listed are both 4 1/3 stops below metered and that the film density under zero flare conditions would arbitrarily be 0.20 above FB+f in either case. In the first exposure, the intensity of light entering the camera is high, and so some of this light (from the portion of the image circle beyond the borders of the emulsion) might bounce around, eventually bouncing onto the film and adding some additional exposure. At least I think it might. Maybe the actual film density ends up being 0.23 above FB+f. In the second exposure, a much lower intensity of light enters the camera, but the shutter is open for longer. Would we still expect a density of 0.23? Or would we actually get the zero flare density of 0.20 because the light intensity is not high enough to cause significant reflections in the camera - even though the film is exposed for longer.
    Same scene, same luminance range, and say shot at two different f/stops should have the same flare. And sorry about the "filter factor" typo. It was supposed to be flare factor.

    Perhaps there is no definite answer. Here's another way to think about the same example. You take a picture of a bright, uniform, featureless mid day sky and expose it to produce an expected net film D of 0.20. In the evening you take a picture of a middle grey, uniform, featureless evening sky and expose it to produce a net film D of 0.20 (so obviously this would be a significantly longer exposure than the picture of the mid day sky). Assume some camera flare in the first exposure leads to an actual net film D of 0.23. Would that occur in the second example too, even though the intensity of light entering the camera is lower? I'm thinking there would be less, or zero flare in the second exposure. Not sure.
    If the featureless sky takes up the entire frame, it's the same as shooting a target. It's virtually a flare free situation, or to put it more accurately, free of the effects of flare.

    Keep in mind this question concerns an in-camera film test with as little flare as possible (aside from some degree of lens flare which cannot be totally eliminated). The aim is to use a brightly lit white card for the entire series of exposures. In actuality, the lens is masked to restrict the projected image to within the borders of the emulsion. In other words, there should be no camera flare. But even though I would be using this mask anyway as an extra precaution, I'm wondering if it is necessary. So my example above would be the equivalent of not masking the lens.
    You're keeping stray light from entering the camera. The exposure of the white card shouldn't be affected either way. Even with an average luminance range the effects of flare at the point of the white card is inconsequential.

    Click image for larger version. 

Name:	Camera Flare.jpg 
Views:	8 
Size:	168.2 KB 
ID:	63191

    Regarding the K-Factor discussion in Henry's book, as it happens I re-read that very section today, and I came away just as little understanding as when I first read the book. I wish he had started by explaining what the K-Factor actually is before getting into the ranges, calculations, standards etc. I still don't get what the K-Factor is. The only thing I think I understand is that it is not what Adams said it was. When you read Adams you come away thinking it is just a safety factor built into the meter.
    With Adams you come away thinking it's a conspiracy. You should read the stuff I wrote n the K-Factor thread. Here's a page.

    Click image for larger version. 

Name:	Defining K, part 2.jpg 
Views:	7 
Size:	224.9 KB 
ID:	63192

    Henry talks about the various values of K, but he doesn't explain what it is or how it relates to exposure. In Henry's book you come away thinking it's an arbitrary decision by the manufacturer. BTW, he never really defines exposure (or from what I've read so far). I like that he has a bibliography, but he could take the level down a notch and include the titles of the papers. The book isn't for scientific publication.
    Last edited by Stephen Benskin; 01-26-2013 at 08:29 PM. Click to view previous post history.

  10. #160
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,278
    Images
    46
    Quote Originally Posted by Stephen Benskin View Post

    Click image for larger version. 

Name:	Camera Flare.jpg 
Views:	8 
Size:	168.2 KB 
ID:	63191
    Michael R 1974,

    Yes Stephen made a tiny typo, he meant Flare factor.

    But look at this chart again. Now imagine doing a single-tone film speed test where you meter Zone V and stop down 4 stops (or 4 1/3 stop if you prefer).

    When you stop down, you move everything down.

    In the middle of the graph, Zone V, the meter point... you see the exposure+flare (realistic exposure) curve practically rejoins the theoretical exposure (45-degree theoretically perfect) curve. So a test exposure is not influenced much by flare.



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin