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  1. #1
    Ian Grant's Avatar
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    Modern Rodinal Substitutes Part II

    Apologies for having to start a new thread but I can't read or even access the first to reply to posts.

    So with a bit of telepathy

    Quote Originally Posted by Kirk Keyes View Post
    Well, there's a problem there, as it's really hard to measure pH accurately when it gets much above 12.5 or so. You have to start getting special electrodes and the like.

    But for MSDS work, it doesn't have to be too precise.
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    Kirk

    A point that's being missed is that A&O give a figure of 2.7% Potassium Hydroxide not 3% in older Agfa MSDS.

    The pH is around 14 sure, but the actual requirement is the pH of the working dilute solution rather than the concentrate which is given elsewhere as pH 11.55, which I commented on in the first post of the thread.

    Way back Ron (PE) mentioned adjustments to Rodinal before bottling, the question we need to ask is are they adjusting on the basis of the concentrate, or also doing some tests on a dilute sample, as this will be a far more accurate indicator.

    Can someone please post a link to this continuation on the original post.

    Ian

  2. #221
    Photo Engineer's Avatar
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    And, they show the same density / contrast differences I saw in the first three samples. I don't care which is which, I just have trouble judging image quality due to those density / contrast differences. As far as the effect you cite, this is why color negative sometimes looks grainier than color reversal. The color neg has such fine grain that you get artifacts.

    PE

  3. #222

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    Quote Originally Posted by gainer View Post
    Let's do it this way. You tell me which of these had the sulfite.
    Print C has more contrast than Print D, so C appears to be sharper. But how can you really be sure if the prints don't truely match?

    Thanks for reposting them so they are the same size.
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  4. #223

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    Quote Originally Posted by gainer View Post
    There is an artifice that will occur in periodic sampling such as digitizing when the original signal has frequency higher than the sampling frequency. The higher frequencies are folded back to the low end. The effect in a photograph with any amount of grain can make the grain look coarser than it would when viewing the photo directly.
    So are you saying one of the scans does not truly represent the print, or are you just unloading a bit of BS on us?
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  5. #224
    gainer's Avatar
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    Quote Originally Posted by Kirk Keyes View Post
    So are you saying one of the scans does not truly represent the print, or are you just unloading a bit of BS on us?
    That BS as you stupidly call it is and always has been very important in almost any branch of science, except possibly the one that defines BS. You will find it and much else you might find useful in "Information Transmission, Modulation and Noise" by Mischa Schwartz. It's in the McGraw-Hill Electronic Engineering Series.

    I am saying no scan that I can get through to APUG in my lifetime with my 26.4K internet service can truly represent any print. I am also syaing that if it takes a 32 power enlargement to show any appreciable difference, then the difference has no practical meaning to me.

    I also described my experiment in sufficient detail that you can repeat it in your own dark place and show me what you think I should have found.

    Why do you act as if you believe I am trying to sell you something?
    Gadget Gainer

  6. #225
    Photo Engineer's Avatar
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    Patrick;

    Would it be too much to ask if the two photos matched in contrast and density? That is my only reservation.

    PE

  7. #226
    gainer's Avatar
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    Quote Originally Posted by Photo Engineer View Post
    Patrick;

    Would it be too much to ask if the two photos matched in contrast and density? That is my only reservation.

    PE
    At the present time it would in fact be more to ask for than I am able to provide. As you know, there is a lot involved in finding the contrast versus developing time for a particular film-developer combination. My equipment for doing the necessary measurements is limited, and my equipment for walking from one end of the darkroom to the other is also limited. Those appendages I used to walk, run and even dance on occasionally (I seem to remember they are called "legs") are causing me great pain.
    No one else seems to be doing anything but theorizing. I am feeling very much put upon because when I try to get some testing of theories started, the criticism of my work seems to be the most important business at hand.

    If I were to change contrast and density, it would be by digital means. If I had done that with perfection, you would never have known the difference. Believe me, the amount of sulfite up to as much as 380 grams per liter of stock has little or nothing to do with grain or sharpness in a 1+50 dilution. The effects will be on storage life of the stock, working life and activity of the working solution.
    Gadget Gainer

  8. #227

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    Quote Originally Posted by gainer View Post
    That BS as you stupidly call it is and always has been very important in almost any branch of science, except possibly the one that defines BS.
    It seems to me it's simply an issue of mismatched contrast indices, and not an issue of scanning...

    I guess I don't see the point of posting scans if pushing the Nyquist limit invalidates the scans. IF that's what is going on...
    Kirk

    For up from the ashes, up from the ashes, grow the roses of success!

  9. #228
    gainer's Avatar
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    Quote Originally Posted by Kirk Keyes View Post
    It seems to me it's simply an issue of mismatched contrast indices, and not an issue of scanning...

    I guess I don't see the point of posting scans if pushing the Nyquist limit invalidates the scans. IF that's what is going on...
    All you need to do to see what happens to apparent granularity is to scan the same print or negative at a number of different scanning rates. Examine a light gray area such as the frame of the window screen behind the easy chair.

    You really ought to repeat the experiment and then chastise me for not having the same CI. After all, these are two different developers, and the best you can do with matching contrast is to get the characteristic curves to cross at some 2 points. If, then, you see that the lines coincide, you're fortunate. Otherwise, especially when comparing small areas between Dmax and Dmin, you will have different values of CI due to differences in curve shape. Certainly, such difference in curve shape need to be investigated, but if the grain, acuity, resolution are not comparable, and the curve shape of the one with better values of these criteria is known and acceptable, why bother?

    So, I say chastise me for not presenting the individual characteristic curves, but not for mismatch of CI. Unfortunately, the phototransisor on my densitometer appears to have died. Since that is also my easel photometer, it is very difficult to match density values at a single point.
    Gadget Gainer

  10. #229
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    The sampling theorem for band-limited signals says that any 2fm independent samples per second will completely characterize a band limied signal of band limit Fm. Our domain is space instead of time, so we have a signal that is made up of grains and expressed in bits per millimeter or other spatial unit. By the sampling theorem, it seems that if you want to characterize fully the real print or negative, you must scan it at high enough bits per mm to see the finest grain.
    Gadget Gainer

  11. #230
    gainer's Avatar
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    I should add that when I sample a small part of the image at 2400 dpi I see finer grain in the printout than at any lower rate. As I said before, the size of that file coupled with my 26.4 K internet speed might not leave me much time to live after it got delivered. APUG might not even be around. It might be like that aerodynamic problem in the early days of mainframe digital that took longer to solve on the IBM 7094 than the mean time between failures.
    Gadget Gainer



 

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