Switch to English Language Passer en langue franaise Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 69,763   Posts: 1,516,210   Online: 1026
      
Page 3 of 4 FirstFirst 1234 LastLast
Results 21 to 30 of 31
  1. #21

    Join Date
    Dec 2005
    Location
    Eastern, Australia
    Shooter
    Multi Format
    Posts
    1,020
    Images
    55
    g'day all
    surely, given all the other variables, measuring accuracy; mixing accuracy; aesthetics; intent; usage; presentation; and on and on, the good old time/temp chart will be pretty close and give a usable outcome

    Ray

  2. #22

    Join Date
    May 2005
    Location
    Woonsocket, RI USA
    Shooter
    35mm
    Posts
    2,725
    Quote Originally Posted by ITD View Post
    Ambient was around 24C, but I guess some of the increase came from heat in my hands and temperature of the tank when I filled it. The water bath took much longer to increase - it took ages to get the dev temperature down until I could find a vessel that would allow a decent depth of water jacket...
    If the in-tank developer temperature changed from 20C to 21.7C over 9 minutes when ambient temperature was 24C, then my guess is that something you could better control was going on:

    • The starting tank temperature may have been at ambient, as you mention. Try pre-wetting your film and wait for the temperature of the pre-wet water to stabilize at 20C before developing.
    • If, as you also mention, your hands were warming the tank and solution, then perhaps you were handling the tank too much. Between agitation cycles, return it to the water bath. If you really think this was a big issue, try minimizing hand-to-tank contact in any way you can, such as by changing from inversion to rotational agitation.
    • You might not have sufficient volume of water to buffer the temperature in your water bath. I use a dishpan tub (mostly for color developing, but occasionally for B&W), which seems adequate.
    • Plastic and stainless steel tanks have different temperature characteristics. Plastic tends to insulate better, which could help if you first bring the film and tank to the correct temperature by a pre-wet. OTOH, steel might be superior for getting quickly to the correct temperature via pre-wet.
    • You might be able to rig something to keep the water bath at a constant temperature. People who do color work often use aquarium heaters for this purpose, but you'd need something else for B&W at typical B&W temperatures. I have no specific suggestions, though.

  3. #23
    Tony Egan's Avatar
    Join Date
    Oct 2005
    Location
    Sydney, Australia
    Shooter
    Multi Format
    Posts
    1,124
    Images
    69
    Quote Originally Posted by Ray Heath View Post
    g'day all
    surely, given all the other variables, measuring accuracy; mixing accuracy; aesthetics; intent; usage; presentation; and on and on, the good old time/temp chart will be pretty close and give a usable outcome

    Ray
    I would agree. I think the science in photography is inherently "sloppy" due to all the variables. I don't mean to say you can be sloppy in technique and expect consistent results but the things some people can agonise over are just not worth worrying about in my opinion. I have used the same Ilford time/temp graph for over 20 years and get consistent results but my technique is always the same for small daylight tank developing.
    - Always aim for 20c as the starting point.
    - If room temp is higher start solution cooler, say 18-19c.
    - If room temp is lower start solution temp higher, say 21-22C
    - Temp will stabilise quite quickly after first 60 seconds of agitation
    - Measure temperature after first 60 seconds of agitation (it is suprising how often I can get almost exactly to 20c based on experience and "feel" for the room temperature and how warm or cool the tank feels in my hands - I don't pre-wash 35mm film or preheat tanks))
    - Measure temp twice again during development (remove cap, stick in thermometer) at approx 1/3 and 2/3 dev time.
    - Extrapolate any temperature changes for average movement up or down during development
    - Adjust final development time accordingly - usually no more or less than 60 seconds either side of "normal"

    I typically use Xtol 1+1 for dev times of 8-12min with 60 sec initial agitation followed by 10 secs every 60 sec.

    And we haven't mentioned all the potential variables in exposure to start with: shutter speed accuracy (across multiple lens), zoom effects, metering process, "in-between" aperture choice, age of film etc etc

  4. #24

    Join Date
    Sep 2002
    Location
    Oregon and Austria
    Shooter
    4x5 Format
    Posts
    833

    Calling Tom Hoskinson and Frotog!

    This discussion has aroused my curiosity about a couple of things. Sorry if this is a "quasi-hijack" to some degree, but I think it belongs here instead of in another thread.

    First questions to Tom Hoskinson: Could you give some instruction to a non-mathematician about how to use the Arrhenius equation in this context? What is the difference between Kelvin and Celsius, how can I derive a new time for a different temperature from a known one?

    And now to Frotog. I would be interested in hearing what evidence you have to support your statements that image color and contrast are also affected by time/temperature changes. Could you elaborate a bit please?

    Thanks in advance to both of you for enlightening me.

    Best,

    Doremus Scudder

    www.DoremusScudder.com

  5. #25
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    As a matter of interest, the Kodak detailed data for CI vs numerous films vs temperature all plot as straight lines on log-log graph paper. There is a slight amount of scatter which is without doubt due to experimental error. All lines intersect at 0 time. The problem with being too precise is that it is not easy for actual work to be as consistent as the average of a number of runs, and never as precise as the theoretial, though it is possible for the theoretical to be less accurate than the experimentally determined values.

    The catch with using this log equation is that one of the constants in the equation is not directly measurable from the experimental data. Also, it's one thing to analyze existing data, and quite another to get data you don't have. In this case, it involves a step density test strip developed under accurately controlled conditions for each of 5 or 6 times and temperatures, each strip to be analyzed by densitometer
    readings to get contrast index.

    My point here is that the variation of CI with time and temperature is certainly consistent enough to be of good use, but it may be easier in the long run just to control the temperature of the developer.
    Gadget Gainer

  6. #26
    gainer's Avatar
    Join Date
    Sep 2002
    Posts
    3,726
    Images
    2
    I forgot to answer your question. The Darkroom Cookbook has a time-temperature scale that works pretty well if you know one successful time. Mark that time and temperature and go parallel to the nearest constant CI line to find the time. This scale is a log scale, you may notice.
    Gadget Gainer

  7. #27
    Lee L's Avatar
    Join Date
    Nov 2004
    Shooter
    Multi Format
    Posts
    3,239
    The attached .pdf file shows the Kodak recommendations for 12 films in D-76 at full strength, roll film, small tank, intermittent agitation at 65, 68, 70, 72, and 75 Fahrenheit. Data points are Kodak's, which are rounded to 15 second intervals according to long established practice. Smoothed lines are done in the spreadsheet. X is temp in Centigrade and Y is recommended development time in minutes.

    Sometimes I learn more quickly from a graphic representation rather than a table of data. I'm reminded of Yogi Berra's admonition, reported as variations on some form of "you can learn a lot by watching".

    Ilford's ID-11 (equivalent to D-76) information sheet is at: http://www.ilfordphoto.com/Webfiles/...1159472874.pdf

    Lee
    Attached Files
    Last edited by Lee L; 05-13-2008 at 11:58 AM. Click to view previous post history.

  8. #28

    Join Date
    Jan 2003
    Location
    NW Chicagoland
    Shooter
    Multi Format
    Posts
    551
    Images
    1
    The Kodak Master Darkroom Dataguide has what they call a developing computer. You come up with a number for your film/developer combination. Either use the Kodak number or find your own. Then you line up the temperature with the number and read the time for that temp. I'm usually within a few degrees and just adjust time using the wheel. For example with number 39 68 deg gives 9m, 75 deg gives 6.5m, 65 deg gives 11.3 min. Seems to work for me over the years.

  9. #29

    Join Date
    Mar 2004
    Location
    Southern California
    Shooter
    Multi Format
    Posts
    3,879
    Images
    11
    Quote Originally Posted by Doremus Scudder View Post
    This discussion has aroused my curiosity about a couple of things. Sorry if this is a "quasi-hijack" to some degree, but I think it belongs here instead of in another thread.

    First questions to Tom Hoskinson: Could you give some instruction to a non-mathematician about how to use the Arrhenius equation in this context? What is the difference between Kelvin and Celsius, how can I derive a new time for a different temperature from a known one?

    And now to Frotog. I would be interested in hearing what evidence you have to support your statements that image color and contrast are also affected by time/temperature changes. Could you elaborate a bit please?

    Thanks in advance to both of you for enlightening me.

    Best,

    Doremus Scudder

    www.DoremusScudder.com
    Here are a couple of Hewlett Packard calculator KEYSTROKE Programs that I generated a long time ago to make the subject Arrhennius calculations.

    ARRHENNIUS FUNCTION 1
    (calculates time at a new temperature, given an activation energy and time at temperature) ARRHENNIUS FUNCTION 2
    (calculates activation energy from Development times at 2 different temperatures)

    00 ( 86 BYTE PROGRAM ) 00 ( 136 BYTE PROGRAM )
    01 >LBL NUTIME 01 >LBL ARHEN
    02 INPUT EA 02 INPUT TMM
    03 STOP 03 INPUT TMN
    04 INPUT TA 04 INPUT TA
    05 INPUT TMN 05 INPUT TB
    06 INPUT TB 06 8.6170881E-5
    07 RCL+ TK 07 ENTER
    08 RCLx K 08 STO K
    09 STO TO 09 273.15
    10 RCL EA 10 STO TK
    11 RCL TO 11 RCL TMM
    12 E^X 12 LN
    13 RCL TMN 13 RCL TMN
    14 XY 14 LN
    15  15 -
    16 STO TO 16 STO T
    17 RCL EA 17 RCL TA
    18 RCL TA 18 RCL TK
    19 RCL+ TK 19 +
    20 RCLx K 20 RCL K
    21 RCL EA 21 x
    22 XY 22 1/X
    23  23 ENTER
    24 E^X 24 RCL TB
    25 RCL TO 25 RCL TK
    26 x 26 +
    27 END 27 RCL K
    28 x
    29 1/X
    30 STO ZX
    31 -
    32 RCL T
    33 XY
    34 
    35 STO EA
    36 RCL ZX
    37 x
    38 E^X
    39 RCL TMN
    40 XY
    41 
    42 STO ZX
    43 RCL EA
    44 END
    Tom Hoskinson
    ______________________________

    Everything is analog - even digital :D

  10. #30

    Join Date
    Mar 2004
    Location
    Southern California
    Shooter
    Multi Format
    Posts
    3,879
    Images
    11
    ARRHENNIUS FUNCTION 2
    (calculates activation energy from Development times at 2 different temperatures)

    00 ( 136 BYTE PROGRAM )
    01 >LBL “ARHEN”
    02 INPUT “TMM”
    03 INPUT “TMN”
    04 INPUT “TA”
    05 INPUT “TB”
    06 8.6170881E-5
    07 ENTER
    08 STO “K”
    09 273.15
    10 STO “TK”
    11 RCL “TMM”
    12 LN
    13 RCL “TMN”
    14 LN
    15 -
    16 STO “T”
    17 RCL “TA”
    18 RCL “TK”
    19 +
    20 RCL “K”
    21 x
    22 1/X
    23 ENTER
    24 RCL “TB”
    25 RCL “TK”
    26 +
    27 RCL “K”
    28 x
    29 1/X
    30 STO “ZX”
    31 -
    32 RCL “T”
    33 XY
    34 
    35 STO “EA”
    36 RCL “ZX”
    37 x
    38 E^X
    39 RCL “TMN”
    40 XY
    41 
    42 STO “ZX”
    43 RCL “EA”
    44 END
    Tom Hoskinson
    ______________________________

    Everything is analog - even digital :D

Page 3 of 4 FirstFirst 1234 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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