Changing densities with development time

Discussion in 'B&W: Film, Paper, Chemistry' started by luxikon, Sep 21, 2009.

  1. luxikon

    luxikon Member

    Messages:
    142
    Joined:
    Feb 13, 2008
    Location:
    Germany
    Shooter:
    Multi Format
    I exposed two APX 100 (135) at 80 ASA. On each film I exposed test frames at Zone I and Zone VIII. The first film I developed at 17°C in 1+50 Rodinal for 21 minutes (rotary development) and achieved d 0.03 at Zone I and d 1.42 at Zone VIII. To get better results I developed the second film as the first but increased development time to 23 minutes.This time I achieved d 0.2 at Zone I but d 1.39 at Zone VIII where I expected a higher density compared to the first film too.
    Can anybody explain this to me? Did I miss the basics of densitometry?
     
  2. ic-racer

    ic-racer Member

    Messages:
    7,517
    Joined:
    Feb 25, 2007
    Location:
    Midwest USA
    Shooter:
    Multi Format
    Technical error in making the exposures.
     
  3. George Collier

    George Collier Member

    Messages:
    1,064
    Joined:
    Feb 23, 2005
    Location:
    Richmond, VA
    Shooter:
    Multi Format
    It's hard to comment on your densitometry from afar :D, but it would be unlikely for that small a change in development to affect the very low values, going in either direction, in my experience. I suspect exposure is different between the two rolls. Maybe a slight, and difficult to notice, change in lighting. You don't mention the shooting conditions (inside, outside, etc), but this is a change in light small enough that it might not be noticed when shooting. You also don't mention how many exposures on each roll of each value, or how much time lapsed between the rolls.
    You might try repeating test, and on both rolls expose all frames, alternating throughout the roll between ZI and ZVIII (to get a good average of your shutter accuracy), then process both rolls together, placing one of them into the tank 2 minutes after the other one, especially since you now have a close sense of the right amount of time.
    It's been recommended, when doing a test like this, to choose a sunny cloudless day, but in open shade, a blank wall, way out of focus (keeps the neg uniform, for reliable readings with the densitometer). This has worked for me in the past.
     
  4. Denis K

    Denis K Member

    Messages:
    237
    Joined:
    Jun 24, 2009
    Shooter:
    35mm
    On your first attempt it looks to me like your Zone I is right at the Base+Fog level. Your second attempt has a significantly higher Zone I level, so I would start by trying to explain that. I think before anyone could help, you will need to tell us more about your exposure, development and densitometry techniques. Unless you have each of these under reasonable control your final readings will be all over the board. Your 17C temperature is lower than I am used to seeing. Is there a particular reason for that?

    Denis K
     
  5. George Collier

    George Collier Member

    Messages:
    1,064
    Joined:
    Feb 23, 2005
    Location:
    Richmond, VA
    Shooter:
    Multi Format
    I just noticed, after posting, that you say the second roll is .2 in the low end (ZI). Do you really mean .02?
     
  6. luxikon

    luxikon Member

    Messages:
    142
    Joined:
    Feb 13, 2008
    Location:
    Germany
    Shooter:
    Multi Format
    Yes, there was a reasonable change in lighting. The first test exposures were made from a white wall in plain sunshine, the second from a white wall on a ship in shade because there was none in bright light. I thought the meter would read them both to 18% gray.
    I think I've to repeat the test the way George proposes.

    @ George
    Yes, as I wrote I meant .2 at ZI.

    @ Denis
    I'm developing APX 100 at 17°C because that produces finer grain as at 20°C and I'm gaining a little more speed. Normally I even go down to 16°C but in summer my JOBO CPP2 doesn't cool down so deep.
     
  7. Anscojohn

    Anscojohn Subscriber

    Messages:
    2,727
    Joined:
    Dec 31, 2006
    Shooter:
    Medium Format
    Your threshold density is almost completely the result of exposure, not development. If it is too low, you need to give the film more exposure, other things being equal.
     
  8. Anscojohn

    Anscojohn Subscriber

    Messages:
    2,727
    Joined:
    Dec 31, 2006
    Shooter:
    Medium Format
    **************8
    You should be photographing an 18% grey card; not a white wall.
     
  9. Bruce Watson

    Bruce Watson Member

    Messages:
    443
    Joined:
    Mar 28, 2005
    Location:
    Central NC
    Shooter:
    4x5 Format
    I think you have an exposure problem. Zone I is usually seen as being at 0.1 over filmbase + base fog. It should *not* be the same as your film base -- it should definitely show some development -- that is, it should show some density above the density of clear filmbase. If your exposure won't give you a good Zone I density then your Zone VIII results from that same exposure are meaningless. That's why the books say you have to find your EI before you find your "N" development time.
     
  10. nworth

    nworth Subscriber

    Messages:
    2,203
    Joined:
    Aug 27, 2005
    Location:
    Los Alamos,
    Shooter:
    Multi Format
    Densitometry can be tricky. Comparisons need identically (or nearly so) exposed spots, and even then your results can vary from one part of the spot to another. I'm not sure what happened, but I would guess exposure changes accounted for the differences. The change in developing time is less than 10 percent, and it would be less than a +1 change with just about anything. In general, increasing development time will increase contrast, not Zone I density. It will usually also increase fog. But it takes 15 to 20 percent added development to shift the contrast by roughly one paper grade.
     
  11. Denis K

    Denis K Member

    Messages:
    237
    Joined:
    Jun 24, 2009
    Shooter:
    35mm
    luxikon, Is this legacy APX-100 or is it Rollei Retro 100 film you are using. I noticed that you measured a density of 0.03 on your first roll. That's real low; hell that's crystal clear. I was just wondering in case I ever needed a 35mm film stock with that clear of a base. I'll bet it would do well as a reversal film; for example as a film for for the dr5 process.

    Denis K
     
  12. DutchShooter

    DutchShooter Member

    Messages:
    64
    Joined:
    Jun 16, 2009
    Location:
    The Netherla
    Shooter:
    35mm
    I measured 0.12 for rollei retro 100 for unexposed base....
     
  13. luxikon

    luxikon Member

    Messages:
    142
    Joined:
    Feb 13, 2008
    Location:
    Germany
    Shooter:
    Multi Format
    @ Denis

    It's legacy APX 100. I zeroed the densitometer after measuring base+fog. Then I measured 0.03 for ZI.
     
  14. Anscojohn

    Anscojohn Subscriber

    Messages:
    2,727
    Joined:
    Dec 31, 2006
    Shooter:
    Medium Format
    **********
    You can reasonably expect that your exposure meter is calibrated to measure an approximate 18% reflectance. Are you taking your exposure reading off such a surface?
     
  15. luxikon

    luxikon Member

    Messages:
    142
    Joined:
    Feb 13, 2008
    Location:
    Germany
    Shooter:
    Multi Format
    No, until now I didn't. I only used any uniform (near) white background because I thought the meter would give me a standardized reading of 18% gray. But I'll take a gray card for my next tests if that helps.