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  1. #11
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    Quote Originally Posted by Mick Fagan
    Hmmm, very interesting piece of information.

    Tomorrow I'm doing a film speed test of a new film I intend to use. But this posting has given me something else to do as well

    I've just figured out a way to insert small pieces of MGIV to the back of my Nikon F3.

    I'll do a few tests on a grey scale and colour chart as well as a pictorial print.

    I don't assume a speed of 25 ISO will be great, but it shouldn't take much time to get a working ISO using your information as a start.

    Nothing like a bit fiddling here and there to keep the grey matter ticking over, eh?

    Many thanks, Mick.
    Mick;

    Please keep in touch. I am most interested in your results, particularly in view of the comments preceeding yours.

    My development was in Dektol 1:3 for 1 - 3 mins by inspection.

    PE

  2. #12

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    Ron, whatever story you like to create, but with EI 25 and developed in Dektol, how do you get 0.1 density above gross fog? You won't get that in daylight.

    Your reference to gamma of 0.62 is incorrect. Gamma is the slope of the straight line portion of the curve, while ASA (and ISO) standard method for b&w negative films specify average gradient or g-bar. They are different quantities measured by different calculation on the sensitometric curve. On the other hand, speed measurement for print emulsion doesn't specify the contrast at all but calculate the speed by 10000 into the exposure (H) to yield the reflection density of 0.6.

    Say an enlarging paper has ISO P500 speed, has short toe and reasonably straight line curve of g-bar of 2. This is typical of fast enlarging paper. That means we need H of 20 to get 0.6 density, and therefore H of 10 or a bit less to make barely discernible exposure above base and fog. Now, ISO b&w film speed can be estimated by dividing 0.8 by this exposure (H), which is around 0.1, even if we accept the g-bar of 2 instead of g-bar of 0.62. Most people expose paper negative at EI of 0.5 to 6 range, lower end of which is more common, because they are not necessarily exposing strictly for the shadow density, but because they consider the image is of sufficient quality if midtone and highlight are registered. So this accounts for the discrepancy between calculation and practice. However, a claim that the sufficient image quality can be obtained at EI25 is way off, based on both experience and calculation.

    I have shared a lot of information about my emulsion as well as processing chemistry with many people on my web site and pure-silver. I have scans of my images made with my emulsion on the web as well. I've even given a free private emulsion-making workshop in Boston to several people.

    In relation to sharing info with you, I've even told you how to desalt emulsions using phthalated gelatin precipitation method, how to manage fogging problems during optimal digestion problem, how to get maximum speed by making core-shell emulsions, etc. but I see you are having problems with the desalting and fog control, at least. I certainly won't bother to post every time I get some data.

  3. #13
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    Here is Ilford MG IV exposed at ISO 25.

    The paper negative was scanned, reversed and inverted to give a proper positive image.

    Included is the similar exposure with my ortho emulsion.

    Please post your own examples before you continue your theoretical comments.

    PE
    Attached Thumbnails Attached Thumbnails iso 25 reversal on ilford.jpg   Paper pos iso 25 agbri dye 4.jpg  

  4. #14
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    Regarding ISO washing and desalting, I have been involed in that since 1965, it is merely a matter of getting commercially available PA gelatin. Nothing has been shared with me at all in any way whatsoever by anyone outside my circle of EK engineers. In fact, I have given the name of one of the sources of my PA gelatin out freely.

    Nothing has been shared with me regarding spectral or chemical sensitization either. All that I have comes from EK or from EK fellow engineers. All that I share outside that circle is not proprietary.

    PE

  5. #15

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    Quote Originally Posted by Photo Engineer
    Regarding ISO washing and desalting, I have been involed in that since 1965, it is merely a matter of getting commercially available PA gelatin. Nothing has been shared with me at all in any way whatsoever by anyone outside my circle of EK engineers. In fact, I have given the name of one of the sources of my PA gelatin out freely.

    Nothing has been shared with me regarding spectral or chemical sensitization either. All that I have comes from EK or from EK fellow engineers. All that I share outside that circle is not proprietary.

    PE
    What a complete nonsense. I have copies of all email correspondense I made in the past. I sent you an email describing how to make phthalated gelatin in 10 minutes, how to use it, and some of the tricks to make good solid curds. I also told you good options as to how you can double wash with minimal work. But it seems that you can't make good use of phthalated gelatin... too bad.

    I also named a few of ortho dyes I have used with good results in Photo.net. In a different thread there, I also told you good antifoggants for both chloride and bromide emulsions. But your emulsions seem to have too high fog level... Oh well.

    If you google enough, you'll also find an infrared dye I use.

    Too much nonesense, this is exactly why I don't want to share any more info with you.

  6. #16
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    Ryuji;

    My problem with ISO washing was obtaining a source of good phthalated gelatin, not with how to carry out an ISO wash. I don't have an organic chemistry lab to synthesize phthalated gelatin, nor does anyone else here I suspect, so I located a source for it. I gave you the name and telephone # of my source. My goal is to give those to the members of APUG so that they don't have to synthesize PA geltin. They are not organic chemists. As a result, your instructions are useless to the majority of the readers here.

    I asked you for the source for your dyes and you didn't give it to me, just the names of the dyes. Again, useless to the readers here. Quite a difference between name and telephone # which I gave you. I will make the dyes that I use available to all users here when my tests are complete.

    In addition, I gave you the ratio of sulfur / gold and levels for different grain sizes. You didn't know them. That also will be published by me. If you publish it, remember, you got if from me!

    Now, all of this is diverting us from the main issue of results. Mine are posted above.

    PE
    Last edited by Photo Engineer; 03-17-2006 at 03:32 PM. Click to view previous post history.

  7. #17

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    Huh? This is insane, Ron. It's amazing how story changes over time.

    I make all my phthalated gelatin myself and they are of very good quality. It takes 5-10 minutes of reaction time. I also make gelatin sheets in dry form after phthalation, which takes more work than phthalation itself.

    I have my data for optimal digestion for different grains, but I don't have yours. But I'm not worried, my grains are core-shell tabular grains of at 3 layers and whatever you have is not applicable to mine. I create sulfur, gold and reduction sensitization centers at different parts of the grain, and my technique is not dissimilar from what's published in literature.

  8. #18

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    I'm really enjoying this thread and you guys are at the top of my list.

    I'll tell you what . . . . I'll serve the martinis (shaken or stirred) if you two will let me sit and listen for awhile.

    What ya think????

    Anyone want olives??

  9. #19

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    No thanks, I'll have tons of Guiness later tonight.

  10. #20

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    SNIP

    Quote Originally Posted by Mick Fagan
    I'll do a few tests on a grey scale and colour chart as well as a pictorial print.

    I don't assume a speed of 25 ISO will be great, but it shouldn't take much time to get a working ISO using your information as a start.

    Many thanks, Mick.

    mick:

    several years ago i compiled a list of (15?) papers and their relative asa's, it was pretty easy, i made 4x5 sheets, stuck them in my speed graphic and made test exposures. i also called kodak and asked them what the asa's were for the few papers of theirs i had in my stockpile ... ( i figured i would compare notes ). i mentioned why i was calling, and asa's i had come up with. they gave me high speeds for their papers, and they made no sense to me. when i mentioned that i had asa 6 instead of 25 i was told film speed and paper speed are measured differently - and then i was told my (film)asa 6 was like their (paper) asa 25 ...

    maybe they only use blue light, and i use daylight or a (xenon) strobe?

    i don't know ... i know that regular old photo paper ( i am using polymax mgfb, kodak mgfb ( old ) and ilford mgfb ) and i use asa 6 and get really good results ... YMMV



    good luck with your tests!
    john
    im empty, good luck

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