Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,773   Posts: 1,516,590   Online: 1066
      
Page 15 of 15 FirstFirst ... 59101112131415
Results 141 to 147 of 147
  1. #141
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    OK then, tell me the procedure for determining the spectral response of an arbitrary photocell. I will want to know the amplitude ratio and phase angle at enough frequencies to enable me to do a convolution with another such response curve that describes a filter. What kind of calibration standards will do this or anything like it?
    Gadget Gainer

  2. #142

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Patrick, I think we are thinking in different directions. I've been trying to discuss design considerations of a densitometer - for testing stained negs. A a color densitometer essentially, so that we can measure the density of negatives at various wavelengths. You seem to be telling me that it can't be done. I don't believe that you actually believe that.

    There are certainly a lot of people that are selling color densitometers out there.

    And I don't think you are trying to convince me that these instruments can't function. They certainly do. They are constructed with care being taken to the spectral properties of the light source, the optical pathway of the design, the spectral properties of the filters used, and the spectral response of the sensor. These manufacturers also supply calibration standards that have been measured under specified conditions. Calibration standards are needed because no matter how ideal our design, electronic parts, or the materials used to built the instrument, it will not have a perfect response. And since the standards have been measured under specified conditions, they should allow us to be able to exchange measurements and then hopefully have a reasonable expectation of comparable results.

    You appear to be headed somewhere else - so I guess I'm not quite sure where you are going with the last post.

    Kirk

  3. #143

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Donald - I knew I should have gone into more details when I made that post...

    First let me say that my comments were based on my experience with PMK, and almost exclusively with PMK. I have used ABC-Pyro, but that was nearly 25 years ago... So my comments in that post and this one here are intended towards using PMK (The concepts I've covered the last 10 pages of this thread could be applied to any staining developer.) And I would only apply my comment about the appearantly lower grain to my experience with PMK. I do understand that ABC-Pyro has a reputation for more grain.

    Donald wrote, "My results are exactly opposite of your suppositions in this regard."

    Which of my suppositions?

    Donald wrote, "The proportional stain exhibited by certain staining developers is counter productive to highlight tonal separation on VC materials. Most notable in this regard is the stain color of the PMK pyro formulation. "

    Donald, I agree that there is not better "highlight separation" when using PMK with VC papers. Not only is not better highlight separations, there is highlight compression. I did not say anything to the contrary about that above.

    What I said was "For graded papers, I find that stained negs print just like non-stained negs. I probably would not bother using a staining developer unless I was using VC papers."

    I would use PMK to NOT get better highlight separation - I would use it to compress highlights - by using VC papers. I was trying to respond to Patrick saying, "Now I am pretty well set for deciding which grade of paper to use. [By using his densitometer.] Heaven help me when I go to VC!" Again, I probably would not bother using PMK with graded papers, although it would give you the option of using a VC paper and then being able to compress the highlights. Kind of a dual-purpose option, again like the PyroCat with alt processes.

    Donald wrote, "In fact the proportional stain is most effective with graded materials, I can not understand your statement about stained negatives printing the same as non stained negatives on graded materials. "

    I guess I need a clarification of what you mean by "most effective". Perhaps we have different goals in mind with our choice of developers. And see the response to the next paragraph -

    Donald wrote, "Have you done any testing of the reflection density in the zone VI and higher tonal regions on prints made from negatives developed in both types of developers?"

    Yes, I certainly have. I found that once you get past the issue of trying to match development times, the shape of a PMK neg printed on a graded paper looks very much like the shape of a non-stained neg printed on a graded paper. The curve has a nice, straight-lined portion in the middle. As far as the graded paper is concerned, the stain looks just like silver. The graded paper can't tell the difference.

    When printing a PMK neg on VC paper, the highlights are compressed and then print darker than a similar exposure would have if a non-staining developer was used (or if the same PMK neg was printed on graded paper). Instead of a straight-lined portion to the curve, you have a curve that is essentially all toe until you get into the darker zone numbers. The toe of the curve on the print is very long.

    I'm not the only one that has found this - it is exactly what Howard Bond found in his second, much better researched article on PMK that was just published in the Sept./Octo. 2004 PhotoTechniques magazine. See his Figure 5. I get the exact same results.

    Are you finding results different from this?

    Kirk

  4. #144

    Join Date
    Dec 2002
    Shooter
    Large Format
    Posts
    6,242
    Kirk Keyes wrote:
    First let me say that my comments were based on my experience with PMK, and almost exclusively with PMK. I have used ABC-Pyro, but that was nearly 25 years ago... So my comments in that post and this one here are intended towards using PMK (The concepts I've covered the last 10 pages of this thread could be applied to any staining developer.) And I would only apply my comment about the appearantly lower grain to my experience with PMK. I do understand that ABC-Pyro has a reputation for more grain.

    I understand your suppositions based on your use of PMK. I have found that other staining developers have different characteristics when used with VC materials. I have found that Pyrocat is neutral insofar as any compression or expansion effects of the highlight tonal scale when used with VC materials. This is based in my testing and experience.

    Kirk Keyes wrote:
    What I said was "For graded papers, I find that stained negs print just like non-stained negs. I probably would not bother using a staining developer unless I was using VC papers."

    I would use PMK to NOT get better highlight separation - I would use it to compress highlights - by using VC papers. I was trying to respond to Patrick saying, "Now I am pretty well set for deciding which grade of paper to use. [By using his densitometer.] Heaven help me when I go to VC!" Again, I probably would not bother using PMK with graded papers, although it would give you the option of using a VC paper and then being able to compress the highlights. Kind of a dual-purpose option, again like the PyroCat with alt processes.

    My results show that proportional stained negatives do print differently then conventionally developed negatives with graded papers. My tests have indicated this to me. This especially true when I print on Azo. In which case not all films will build the density range required of this paper without using staining developers. The proportional stain acts as additional density in the upper density regions.

    I can't understand anyone wanting to compress the highlight tonal scale in a print. That is the reason that I use proportional staining developers...to effectively gain increased separation. It would appear that if compression is the desired result that reduced development would suffice.

  5. #145

    Join Date
    Mar 2003
    Location
    Greenville, SC
    Shooter
    Large Format
    Posts
    4,813
    Images
    5
    Quote Originally Posted by Donald Miller
    My results show that proportional stained negatives do print differently then conventionally developed negatives with graded papers. My tests have indicated this to me. This especially true when I print on Ago. In which case not all films will build the density range required of this paper without using staining developers. The proportional stain acts as additional density in the upper density regions.
    Donald,

    I don't think you and Kirk have any fundamental disagreement. He is saying that with graded papers stained negs print just like non-stained negs. You are saying that the proportional stain acts as additional density in the upper density regions. Both statements are essentially true.

    What one can say is that when developed to the same effective printing contrast, as measured by the spectral response of the process, stained and conventional negatives print virtually the same. I am not going to say exactly the same because there is one area where I find that even with graded papers tanning/staining developers give better results, and that is when printing strongly backlit scenes. Since development with tanning/staining developers is mostly at or near the surface there is less light scattering than with conventional developers, and this results in keeping detail even in extreme lighting conditions, say when photographing a tree with leaves against a very bright object like the sun.


    Sandy
    Last edited by sanking; 08-22-2004 at 11:40 PM. Click to view previous post history.

  6. #146

    Join Date
    Jun 2004
    Location
    Portland, OR
    Shooter
    4x5 Format
    Posts
    3,268
    Sandy wrote, "I don't think you and Kirk have any fundamental disagreement. He is saying that with graded papers stained negs print just like non-stained negs. You are saying that the proportional stain acts as additional density in the upper density regions. Both statements are essentially true."

    Sandy, I do agree with everything said in that paragraph.

    Sandy wrote, "What one can say is that when developed to the same effective printing contrast, as measured by the spectral response of the process, stained and conventional negatives print virtually the same. I am not going to say exactly the same because there is one area where I find that even with graded papers tanning/staining developers give better results, and that is when printing strongly backlit scenes."

    I also agree here - please note that I said that "the shape of a PMK neg printed on a graded paper looks very much like the shape of a non-stained neg printed on a graded paper." I can not say that they are identical, but they are very similar.

    Sandy, thanks for giving an example that one would not observe from printing step wedges but only from shooting real world subjects! It is easy to get wrapped up in testing stuff and forgetting the ultimate application. I'm not saying we should not do testing, but it is good to remember that the tests we usually do, do not always tell us everything about our materials.

  7. #147
    rwyoung's Avatar
    Join Date
    Apr 2006
    Location
    Lawrence, KS
    Shooter
    Multi Format
    Posts
    704
    Images
    40
    Quote Originally Posted by Ed Sukach View Post
    I've used logarithms a LOT, having been in the "pre-PC" era.

    ... snip ...

    Wow... what a memory exercise this has been. This is equal to trying to remember how to calculate square .. or cube roots - by hand!!
    Searching for other information came across this old thread and couldn't resist. Ed, and I'm sure you do remember this,

    (any base log would work but I'll just use 10 for this example and ^ for "raise to the power")

    log10(X^Y) = Y * log10(X)

    So to find the square root of 99,

    99 ^ 0.5, now get out the tables or slide rule:

    Do the log : log10(99) = 1.996
    Multiply for the power : 0.5 * 1.996 = 0.998
    Do the antilog to get the result : 10 ^ 0.998 = 9.950

    Cube root of 99? 4.626 by same method...

    Don't sweat the petty things and don't pet the sweaty things! http://rwyoung.wordpress.com

Page 15 of 15 FirstFirst ... 59101112131415


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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