Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,000   Posts: 1,524,344   Online: 783
      
Page 3 of 3 FirstFirst 123
Results 21 to 28 of 28
  1. #21
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Attached is a Film Speed / Contrast Index curve of two different speed determination methods from the same set of data. Except for CI 0.61, the the exact same film curves produce different film speed values.

    The differences aren't great and the biggest differences are at the extreme ends which are less frequently used. The choice of one over the other isn't going make or break an exposure, but it does bring up the question as to which one best represents the relationship of exposure to quality (which is what film speed is).

    And even if it doesn't matter to a person the the method they are using produces the most accurate results because they are happy with their images, this example should at least illustrate that when two people are discussing speeds from a particular film, they could be talking about two very different things.
    Attached Thumbnails Attached Thumbnails DeltaX EFS CI - EFS.jpg  

  2. #22

    Join Date
    Jan 2005
    Location
    Downers Grove Illinois
    Posts
    1,050
    There are a few developers that give a true small speed increase, maybe 1/2 stop. The rest give more contrast to an underexposed neg, ie no shadow detail, so it is easier to print. There the shadows merge and there is no tone separation. Looks terrible if you like fine art.

    If you expose 1 stop more than box speed, you get more shadow detail and finer grain, much finer grain because you cut back development time 20%.

    Grain is from time in developer and diluted developer. Shorter time, more concentrated developer, gives less. The downside is some loss of sharpness because of developer dilution.

    one half box speed, 1:1 developer, cut time 20%, is a kind of sweet spot for fine art photos.

  3. #23
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,134
    Quote Originally Posted by Gerald C Koch View Post
    This is a very complex question really outside of the scope of APUG to answer. .....
    Questions like this are what APUG is all about.

  4. #24
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,157
    Images
    46
    Quote Originally Posted by Stephen Benskin View Post
    I remember using a seasoned T-Max R/S in a dip and dunk Refrema. It produced close to the ISO speeds at normal development with TMX and TMY, but for many of the conventional grain films, it was too active. It tended to obtain normal contrast before the film speed had a chance increase to a desirable level. HP5-P was an good example of this. For a contrast index of 0.58, the processing time was 3:30 seconds (very short). The effective film speed only reached around 100 (for a 400 speed film).... The way we fixed the low speed was to reduce the activity of the developer by adding a small amount of acetic acid to lengthen the development times need to achieve CI 0.58 which gave the lower densities more time to build. .... With a few additional chemicals, I was able to bring it up slightly past ISO speed...
    This makes a lot of sense.

  5. #25
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Quote Originally Posted by daveandiputra View Post
    My foremost reason to ask about this is very practical, which is how to know what speed does my current combination of developer and film is best at.
    My impression is that the OP is more interested in testing procedures than the chemical composition to increase film speed. Maybe he's interested in both. Still, I believe the little discussed topic of testing methodology is an important one (this applies to both speed and contrast determination). One of the stated purpose of the ISO B&W film speed standard is to produced a value for the purposes of comparison between different film types and manufacturers. How productive is it to discuss film speeds when one person is referring to speeds obtained with the Zone System method and another to speeds using sensitometry when we know that under the exact same film/developer/processing conditions, the two methods will produce speeds differing by 1/2 to one stop? (How the film speed is applied toward making an exposure is an entirely different issue (EI).)

    Then there's the question of the accuracy of the methodology. Photographers have been making quality images since the invention of photography even though there wasn't a "film speed" until around the beginning of the 20th century. After the introduction of inertia speeds, photographers and the growing number of amateurs continued to produce excellent images, so why the changes in the methodology over the next 40 years (see the attachment - "Emulsion Speed Rating System")? If quality pictures can be made by a given method, so why the change?
    Last edited by Stephen Benskin; 09-04-2011 at 07:24 PM. Click to view previous post history.

  6. #26
    Bill Burk's Avatar
    Join Date
    Feb 2010
    Shooter
    4x5 Format
    Posts
    3,157
    Images
    46
    Your Refrema example is so clear and answered exactly what the OP originally asked. How can you lose a stop of speed just by changing developer?

    The surprise in your example... a "more active" developer reduced speed. The reason makes sense once you explain that you had to take the film out before the highlights blocked up, but the shadows had not had a chance to emerge.

  7. #27
    Stephen Benskin's Avatar
    Join Date
    Jan 2005
    Location
    Los Angeles
    Shooter
    4x5 Format
    Posts
    1,218
    Attached are two papers on contrast determination. The scientific paper on Contrast Index published in Photographic Science and Engineering, and a nice little comparison of different methods published in the British Journal of Photography, "Contrast Measurement of Black and White Negative Materials."
    Attached Files

  8. #28
    daveandiputra's Avatar
    Join Date
    Jul 2010
    Location
    Jakarta, Indonesia
    Shooter
    35mm RF
    Posts
    192
    Wow, I'm going to read all the threads real slow to really understand it this is very advance for me. thanks to Steven and others for the input and contribution.

Page 3 of 3 FirstFirst 123


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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