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  1. #101
    Bill Burk's Avatar
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    Hi PeterB,

    You can jerry-rig your camera underneath your enlarger to take advantage of the shutter. Or maybe use electronic flash as the light source.

  2. #102
    Bill Burk's Avatar
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    Quote Originally Posted by Stephen Benskin View Post
    Peter,

    ...BTW, a good way to calculate aim CI is:

    desired negative density range / (log subject luminance range - flare)

    Example: 1.05 / (2.2 - .40) = 0.58

    ....
    Wow, so simple and easy to prove. I'll keep this posted by my densitometer!

  3. #103
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    To project contact print the step wedge....

    I've been thinking about the rationale behind doing a contact print rather than having the film in the camera to photograph the step wedge and wondered why Ralph would have written "Alternatively, you could contact print the step tablet onto film, but that will eliminate flare altogether, which is not realistic. "

    Its a shame he isn't available to reply right now to defend his thoughts, but I'm not convinced just yet to perform a contact print of the Stouffer step tablet as it will take me a lot more setting up (to rig some shutter to my enlarger or measure the output of a flash unit) and trial and error to get the exposure and other details right. I am using 120 roll film which also makes a contact print more fiddly especially in total darkness (I don't have a safelight for film if there is such a thing).

    What Stephen writes regarding eliminating the lens from the test makes sense in theory, but in practice I'd also like to hear about the experience of others who have done both methods to assess how much value doing a contact print really confers over the projection method.

    regards
    Peter

  4. #104
    Usagi's Avatar
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    The enlarger is easy, the shutter is really not needed.

    I tried to use flash method but really could not determine the exposure. As I don't have shutter on my enlarger, I used the 0.6 second exposure. Phil Davis suggest in his BTZS book time 0.4s (If I recall right) but I have to use longer to ensure get enough exposure. My enlarger's bulb need 0.1 sec for turning on and 0.1 sec for turning off (measured simply by recording movie with digicam. Precise enough).

    My fear was that turning on and off times would not stay consistent and affects the exposures, but I didn't found any proof for that. The result is very consistent.

    Before using enlarger, I tried to photograph step wedge by using various lighting systems. The light was always uneven. I also tried to tape wedge to window with and without diffuser but the background was always problematic (as did the exposure time during autumn/winter/spring).

    One different approach is to photograph gray card and vary the aperture and shutter speed. I have used that a lot with MF and 35mm films as I have precise shutters in those cameras. With mechanical shutter I would not use that kind of test.
    However it's easy way to get CI values. Or a rough charasteristic curve.


    ps. I like to get flare in the results by photographing target, but as it's not an option with my equipments in large format cameras, I use contact method.
    Also the flare depends on the lens and with large format cameras I have lot of very different lenses so inclusion of flare by photographing step wedges would require almost own test serie for each lens.
    MF and 35mm lenses are good enough to have 'consistent' flare..

  5. #105
    Stephen Benskin's Avatar
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    Quote Originally Posted by PeterB View Post
    "Alternatively, you could contact print the step tablet onto film, but that will eliminate flare altogether, which is not realistic. "
    Peter,

    You need to think of testing the film and testing the camera as two separate things. Take a look at the flare test I uploaded. What I did is to make identical exposures using the black box described by Davis. The only thing that changed were the boards I had surrounding the opening. One was black, one was gray, one was white, and one was a mixture of all three. After shooting them, I then make a sensitometric exposure (that's where the curve is from). Notice how even though the exposure never changed, there's a 0.39 log-H difference between the black surround and white surround.

    Now ask yourself, how can you get a reliable film speed from this method? Your test showed a great deal of flare. How much should it be and how can you confirm the amount?

    Contacting is simply the way it's done. Ralph's correct in that it's unrealistic to assume there isn't flare in the system, but that doesn't mean it has to be included during the exposure part of the film testing only that it needs to be factored in. This can be done at the interpretation / evaluation stage. The ISO standard for B&W film speed specifies contacting the film, but it's the methodology of the film speed determination that has a stop of flare factored into it.

    I recommend reading Photographic Materials and Processes by Stroebel et al or Sensitometry for Photographers by Jack Eggleston.

  6. #106
    Bill Burk's Avatar
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    Hi Peter,

    Stephen's got it right.

    Flare is important. So it's right for Ralph to recommend testing that includes it.

    But it's a better science experiment to eliminate as many variables as possible.

    Contacting will eliminate Flare.

    Then later you can do a black box test to measure how much flare you have in your camera.

    You can paint the inside of a coffee can black and take it out with you and put it in real scenes to perform flare tests, without doing any additional "work". As you take these pictures note the brightness ranges and describe the subjects.

  7. #107
    PeterB's Avatar
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    Thanks Stephen. My main opposition (up until now) to doing it via the contact method is that Ralph's book (WBM) and his replies to date in this thread have never pushed it to the point you have which left me with the distinct impression it would be acceptable to carry on with the camera lens in the light path. Perhaps Ralph is assuming we must prevent all other sources of non image light from hitting the lens (the image being the step tablet). And after my learning experience above, I too agree that it is necessary to eliminate all light from around the step tablet and coming in from the sides in the air between the tablet and the lens.

    Quote Originally Posted by Stephen Benskin View Post
    Ralph's correct in that it's unrealistic to assume there isn't flare in the system, but that doesn't mean it has to be included during the exposure part of the film testing only that it needs to be factored in.
    Ralph suggests we deal with flare by using the nomograph in WBM. "In addition, the use of certain equipment, like the type of enlarger or the amount of lens flare, influences the appropriate average gradient and final film speed. The nomograph in book provides an overview of these variables and their influence. The Zone System is designed to control all these variables through the proper exposure and development of the film. This requires adjustment of the manufacturer’s film speed (or ‘box speed’) and development suggestions." (copied from page 1. of the FilmTestEvaluation.pdf he links to in this thread)

    Ralph has decided not to push the contact method because of the above approach he takes with the nomograph. He is ignoring the (supposedly small) effect of the flare from the less dense steps in the tablet).

    The experiments you conducted Stephen give MUCH larger areas of light which add flare to the image (compared to flare from the few small lighter steps in the tablet). In fact on my Stouffer 31 step wedge each step is only 4mm x about 15mm in size - small compared to the nominal 56x56mm frame size of the negative.

    regards
    Peter

  8. #108
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    Thanks for your replies Usagi and Bill.

    Usagi, I too would be concerned about the repeatability of switching an enlarger on and off with the ramp up and down of the light intensity. Rather than waste another 5 rolls of film I would rather first do some test to convince myself of its repeatability.
    My light meter measures flash output with and without a synch cable attached (I just have never tried it), and it is possible that such light meters can measure/integrate the light intensity over times longer than the micro seconds a typical flash burst lasts.

    Having said that I am still trying to convince myself that the in-camera method can work for me (see my last post to Stephen)

  9. #109
    Bill Burk's Avatar
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    Hi Peter,

    I don't want Ralph to come back and say we hijacked his thread and tried to change his method.

    So go for it with your current setup, which is in line with the Way Beyond Monochrome testing instructions.

    Mask your test wedges and make the best lens shade you can.

    Expose the strips for three or four more stops of light than you did last time.

    Hopefully, you will find N somewhere near 12 minutes and you will have some densities near 2.0

    Flare was messing with your toe densities that were supposed to be under 0.1.

    Underexposure was keeping your dMax under 1.0 when it could have been 2.0

    Because you are not using "modern" lenses, you may still have higher toe densities than Ralph, but it will be a model of your camera system.

    Bill

  10. #110
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    Excellent ! Thanks for your blessings Bill ! Ralph should be pleased that I stuck to his method.



 

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