Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 33

Thread: Scientific reason why some developers causes decrease film speed

  1. #21

    Join Date
    Oct 2020
    Posts
    19

    Re: Scientific reason why some developers causes decrease film speed

    Thank you very much all, and apologies for incorrect use of film speed. But thankfully some of you have understood me
    I understand speed is measured for little density change in shadow areas and some developers give better results on those areas.

    Purpose of my question is because I’m asked to write a post for reader in Turkey about technical bits of film, chemistry and everything about it. Due to currency economic situation, they don’t have a chance to try all the different developers and I got the task at least to show them different developers as well. Otherwise I’m all the way HP5, F100, Rodinal and XTOL guy and tried DDX in the past so I have a good selection of comparative negatives.

  2. #22

    Join Date
    Jul 2008
    Posts
    3,145

    Re: Scientific reason why some developers causes decrease film speed

    Simplified summary, Silver Bromide in the film reacts with light reaching these SB crystals. Conversion of these SB crystals altered by light becomes metallic silver during the reduction process known as "Developing". Size of these silver bromide particles in the film relates to the film's sensitivity to light NOT "speed of the film".

    Developers commonly consist of a developing agent (Elon-Metol, Phenidone, Pyrogallic, Amidol, hydroquinon, Glycin, Pyrocatechin and...) this is the chemical that acts to reduce the SB particles that has been affected by light into darkened metallic silver. To speed up this process an alkali like sodium carbonate or potassium metaborate or borax is added to increase ph. A Restrainer like potassium bromide to moderate the alkali accelerated development agent to reduce film fogging and a preservative like Sodium Sulfide. Large amounts of Sodium Sulfide results in solvency which has an effect of "washing away" some of the film grains resulting in what is perceived as "finer grain" grain developed film trading off acutance or edge effects.

    Mild acidic stop bath rapidly halts the SB reduction process.

    Fixer is a solvent that removes the non light reacted SB particles and other stuff like the anti-halation layer.
    Click image for larger version. 

Name:	Foto Chem.jpg 
Views:	4 
Size:	65.5 KB 
ID:	216930


    To deny developers and development time does NOT have an effect on effective film speed is ignorant of what information is contained in the Gamma curve and how this related to print making. This is where a good densitometer can be extremely useful. Or, at the very least a good 18% gray card and stepped gray strip.

    ~Note there IS a difference between innate light sensitivity of a B&W film -vs- effective film speed. These two terms are NOT interchangeable and have distinct meaning.

    The effective speed of a B&W film depends LOTs on the contrast range of the scene to be imaged, development process and print making process. It all works together as a system with the finished print as it's goal. This is why testing to determine effective film speed for a given film and amount of exposure driven by how the negative would be made into the finished print is SO important and why the "box" speed of the B&W film is not often relevant to gain proper control over the print making process.

    Fact remains, a GOOD B&W film negative is much easier to print and allows artistic alterations during the print making process. Inferior negatives forces a struggle to make a some-what ok print.

    While this applies to the traditional wet dark room print making process, due to the wide spread of scanning of negatives into digital files then "worked over" in software, it appears these time proven methods to produce good print making film negatives have become ignored in favor of "fix it in software"..



    Bernice

  3. #23

    Join Date
    Jul 2008
    Posts
    3,145

    Re: Scientific reason why some developers causes decrease film speed

    One more on the topic of "film speed"..

    ~Testing Black and White Film~
    https://www.kennethleegallery.com/ht...hutter%20speed.


    "Executive Summary: Almost everyone who does rigorous film testing ends up shooting at roughly one f/stop slower than box speed for normal development: 200 for HP5+ and TMY, 50 for FP4+ and TMX, etc. The more important issue is determining the development times which work for you. Even then, if your results are substantially different from others, you're probably doing something wrong."

    Why?
    Bernice

  4. #24

    Join Date
    Sep 1998
    Location
    Oregon now (formerly Austria)
    Posts
    3,036

    Re: Scientific reason why some developers causes decrease film speed

    Faith,

    Maybe Stephen Benskin will chime in here: He and Michael R seem to be the real experts in this field, along with a few others. If he doesn't you may find answers by searching his older posts here and over on Photrio. Or you could PM him.

    It seems to me that a lot of the discussion here confuses emulsion speed with personal E.I. (exposure index) that many photographers determine for themselves and which is based on a lot of rather non-scientific considerations including equipment variables, personal preference for shadow detail and separation, safety factors, metering techniques (e.g., consistent errors in metering or one's tendency to not place shadow values in the Zone one really wants, etc.).

    ISO emulsion speed, while directly related to the "first excellent print" test, is defined by contrast gradient and curve shape, and a host of other emulsion-density-specific parameters including specific developer(s).

    Some other developers do seem to affect the effective emulsion speed somewhat, as does developing to a higher or lower contrast than ISO standard. The former seems to be what you are interested in. There's a lot of discussion on this thread about topics tangential to this, which seem to me to not be what you asked about...

    Best,

    Doremus

  5. #25

    Join Date
    Jul 2008
    Posts
    3,145

    Re: Scientific reason why some developers causes decrease film speed

    Seems the root of this mis-understanding is much about the designed sensitivity of a given film to light (mostly fixed)-vs- effective film speed (mostly variable) which are two completely different items and are NOT interchangeable.


    Bernice

  6. #26

    Join Date
    Oct 2020
    Posts
    19

    Re: Scientific reason why some developers causes decrease film speed

    Also a similar question could be asked, why developer A is better than developer B for push processing.

    So the info I could collect is;
    Fine, extra fine grain developers causes a bit of speed loss due to solvent
    High accutance developers causes a bit of increase
    Rodinal, due to high dilation, works as compensating developer can cause a bit of loss

  7. #27
    Peter De Smidt's Avatar
    Join Date
    Jan 2001
    Location
    Fond du Lac, WI, USA
    Posts
    8,337

    Re: Scientific reason why some developers causes decrease film speed

    Phenidone developers tend to give about a 1/3 stop boost over D76.
    “You often feel tired, not because you've done too much, but because you've done too little of what sparks a light in you.”
    ― Alexander Den Heijer, Nothing You Don't Already Know

  8. #28

    Join Date
    Oct 2020
    Posts
    19

    Re: Scientific reason why some developers causes decrease film speed

    Quote Originally Posted by Peter De Smidt View Post
    Phenidone developers tend to give about a 1/3 stop boost over D76.
    That’s great to know, XTOL and Microphen has it. I wonder why Rodinal manual says it has high emulsion speed yield when we know high dilation causes speed loss.

  9. #29

    Join Date
    Sep 2014
    Location
    Montreal, Canada
    Posts
    1,113

    Re: Scientific reason why some developers causes decrease film speed

    Nice try. The root of the misunderstanding is bad information repeated over and over and over.

    Quote Originally Posted by Bernice Loui View Post
    Seems the root of this mis-understanding is much about the designed sensitivity of a given film to light (mostly fixed)-vs- effective film speed (mostly variable) which are two completely different items and are NOT interchangeable.


    Bernice

  10. #30
    Bill
    Join Date
    Oct 2017
    Location
    Houston, TX
    Posts
    64

    Re: Scientific reason why some developers causes decrease film speed

    For those interested in some further reading, here is a good paper on the subject: Film processing for maximum sensitivity at moderate contrast. It is written by Lockheed for aerial photography purposes, and explores increases in both actual and effective film speed based on the developer. It is available free on Sci-Hub by pasting in the DOI, 10.1117/12.933997.

    A line near the beginning:

    "The developer and process reported in this paper could generate negatives within the ANSI contrast rules that still gave light meter measured best exposures 2 and 3 times the calculated ASA speed."

    Likely not useful except very infrequently, but it is interesting reading.

Similar Threads

  1. Decrease exposure, increase dilution or decrease development.
    By drgoose in forum Darkroom: Film, Processing & Printing
    Replies: 4
    Last Post: 24-Apr-2016, 18:02
  2. Does developer temperature increase/decrease contrast?
    By Kimberly Anderson in forum Darkroom: Film, Processing & Printing
    Replies: 4
    Last Post: 28-Oct-2014, 19:53
  3. Kodak X-Ray film price DECREASE!
    By Tin Can in forum Darkroom: Film, Processing & Printing
    Replies: 0
    Last Post: 5-Jun-2014, 09:57
  4. Image circle increment wrt to decrease in subject distance
    By sweat100 in forum Lenses & Lens Accessories
    Replies: 6
    Last Post: 10-Apr-2013, 05:52

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •