Film test. Did I screw up totally or?

Discussion in 'B&W: Film, Paper, Chemistry' started by Robert, Jun 25, 2003.

  1. Robert

    Robert Member

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    I did a film test putting my home built densometer to use. [Seems to work just fine] Here is the problem. I've been using the motorbase since I got it but of course today I forgot to cut my time down. The zone VIII number is much higher then it should be [1.742] which I think shows over development. Makes sense since I should have used 17 minutes and not 20.

    Getting to my question is the zone I info valid? The test shows I've got a personal EI of 64. .11 over base fog. I think I should be okay since in the Ansel system of testing you first do Zone I and then do separte tests for Zone VIII.
     
  2. Donald Miller

    Donald Miller Member

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    If you are basing your EI on the .11 density above FB+fog, then the EI is accurate. If you did your development test based upon film shot at the EI determined in the first step then the development test is valid. If the development test is valid, then the density that you show is indicative of too long a development time. That is a density that would be suitable for contact printing on Azo (althought a bit high for that) but certainly much too high a contrast for conventional enlarging. For a diffusion light source 1.20-1.30, for a condensor light source 1.10-1.20 are what I strive for on a VIII value density. I would think that you need to reduce your time by more then 3 minutes based upon the times you related and the density that you indicated.
     
  3. Donald Miller

    Donald Miller Member

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  4. Robert

    Robert Member

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    Thanks basically what I was hoping for. Just need to nail down the development time now.
     
  5. Thilo Schmid

    Thilo Schmid Member

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    Robert,
    you should take into account:

    - a density of 0.11 for Zone I is only valid, if the density for Zone VIII is valid, too. Otherwise you will have to adjust development time and thus will get another density for Zone I, too

    - The measurement characteristics of your densitometer must match the characteristics of your enlarger. If your densitometer uses diffuse light and your enlarger has a condenser, the results will not match. Take some readings with your lab meter and your enlarger to verify the results
     
  6. Jorge

    Jorge Inactive

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    I hesitate to do this, but this information is wrong and goes against every principle of sensitometry.

    The densitometry has nothing to do with the type of light the enlarger uses. Densitometers do not use diffuse or colimated light. all they do is pass a beam of light through a small section of the film and the diference in opacity from the reference beam is detected by a photo sensor. If anything all densitometers are "diffused light" as the light gets scattered by the film.

    The toe of the film curve is affected very little by developing. ALthough Robert is very close to the treshold, small amounts of developing changes would not affect the zone I value. And even if they do, is easy to compensate for this by reading the zone I value and adding the appropriate extra exposure. For example if he gives 3 minutes less developing and notices his Zone I value has gone from 0.11 to 0.09, all he has to do is add 1/3 stop to the film rating to bring him up to the adequate zone I values. He certainly does not have to make paired test every time he changes developing times.

    I stress again the density range one aims for to use with diffused or colimated sources has nothing to do with the light source used in the densitometer.
     
  7. Thilo Schmid

    Thilo Schmid Member

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    Jorge,
    I beg to differ. The measurement charachteristics is important and is usually indicated with the technical data (and is the reason why you can change the aperture on some densitometer models). The Callier Effect will not change the basic shape of the caracteristics curve (well - there are people, who believe it does), but it will for sure change the grade. This is the reason why you usually have different development times for condensor and diffuse light enlargers. You may, of course, apply arbitrary correction factors in this case. But this would indeed be "against every principle of sensitometry". The Callier Effect depends on light aperture, grain size and grain shape and you will need different correction factors for different types of film/developer combinations. To be exact, you would have to calculate backwards from paper densities to receive the desired negative densities you should tune your development process to.

    There is a good document about this availiable under: http://www.gigabitfilm.de/download/callier_effekt.pdf (esp. the second part about the different measurement geometries on transparent targets)
    Unfortunately, it is written in German, but some translation program might help.
     
  8. Jorge

    Jorge Inactive

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    Yes, but the callier effect you are talking about applies to enlarger light source not to densitometer light source. The reason some densitometers have the ability to vary the sampling aperture is so that you can sample a smaller area of the film, not to try to simulate "difuse or colimated" light sources this is very well explained by the late Dr. Henry. Now if you are talking about spectrometry in thin film applications then that is another matter, but then we get into micro meter densitometers which is entirely a different matter.

    One of the best books in this matter is photographic sensitometry by Todd and Zakia, and I will quote " The present United States Standard specifies diffuse measurements, and all commercially available instruments are said by their manufacturers to conform to this standard in terms of results. Consequently, if we wish to make specular density measurements, we must design our own equipment, or modify existing equipment." So even if you wanted to make specular measurments you would have to have a detector that was away from the film, not in contact as all densitometers work presently. trying to simulate density measurements by specular or difuse source is not practical, and since there are no correction factors to convert either way, for all practical purposes diffuse measurements are the rule.
     
  9. Thilo Schmid

    Thilo Schmid Member

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    Jorge,

    the Callier Effect is independent of whether the light hits the sensor of a densitometer or the paper. But the densitometer can only take this into account, if he has the same light source.

    You should adjust film development to your enlarger and not to your densitometer. If your densitomenter has the same light characteristics as your enlarger, it will produce the same results. Otherwise, your enlarger will produce different paper densities than expected. Again: you may apply some correction factor here, but this will depend on film/developer combination.

    BTW: the densitometer settings on my device do not affect the measurement area at all, which is determined by the corresponding hole in the case and the probe size, which is always the same.
     
  10. Jorge

    Jorge Inactive

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    Arrrghhh...exactly, you develop for the type of enlarger, all current commercial densitometers are of the diffuse type, they all measure diffuse light. Again, if you want a densitometer that will measure specular light similar to a collimated condenser enlarger you would have to MAKE one.......I never said you have to adjust developing time to a densitometer, I said there are no densitometers which measure specular light similar to a condenser enlarger.
     
  11. Thilo Schmid

    Thilo Schmid Member

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    Much simpler: use your enlarger and your lab meter, as I have suggested initially.

    BTW: these densitometers do exist and are called "micro densitometers", which in this case does not mean that their probe size is very small.
     
  12. Robert

    Robert Member

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    Well my home made meter uses my enlarger for a light source. So what does that mean?
     
  13. Thilo Schmid

    Thilo Schmid Member

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    Well Robert, we must have been very technical. Your densitometer is perfect for this case, because it has exactly the same light source as your enlarger...
     
  14. Jorge

    Jorge Inactive

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    micro densitometers are used in thin film applications and this is a totally differnt field from photography. they cost thousands of dolars and you never see one on the market...they are made specially for people like Dupont, Dow Agfa...etc...
     
  15. Loose Gravel

    Loose Gravel Member

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    Robert, be careful. It is easy to get a miss reading with a 'projection' densitometer. There can be spacial and/or temporal variation in the illumination that can throw off your null reading. Spacial variations can be eliminated by not moving the sensor and by moving the negative instead. Temporal variations are probably not an issue unless you are using coldlight. If so, make sure it is warmed up and that you check it at the beginning and end.

    Good luck.
     
  16. Robert

    Robert Member

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    I'm guessing a projection densitometer would be one that puts the negative in the enlarger? I'm just using the enlarger to project a circle of light on the baseboard. The sensor is sitting on the baseboard with the negative right on it . It's a condensor enlarger.
     
  17. Loose Gravel

    Loose Gravel Member

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    Robert, one more thing. What does your detector look like? I used to have the transmission densitometer standard around here, but I can't find it. Anyway, in that standard it defines how the negative shall be illuminated and the light from the sample is measured (the angle). Basically, if the light source is collimated, as through an aperture, the sensor should read as much of the resulting light coming from the negative, i.e. the sensor should have an 'integrating sphere' design. If the light source is diffuse, then the sensor should 'see' only a narrow angle. All angles on one side, narrow angle on the other.

    A different density results if this is not followed, because of the Callier effect. This difference only matters if you want to be able to compare numbers with those in books.

    It sounds like your light is collimated, therefore your sensor should have an integrating sphere or some kind of integrating quality. It needs to be able to see light coming from all angles of the negative. If the negative is in direct contact with the sensor, this works. Or if you put a piece of white Plexiglas in contact with the negative and then the sensor looks at the back of the white Plexiglas, this works too. Unfortunately, the Plexiglas attenuates the signal.

    You could turn this around and do it on top of a light table. Mark a small area on the light table, put the negative there and put the sensor on top looking down. This is good if your sensor is not an integrator and sees only a narrow angle.

    Hope this makes sense. Maybe someone out there has the standard and can correct any inaccuracies.
     
  18. Robert

    Robert Member

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  19. ptempel

    ptempel Member

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    I think you're on track. Since you have a home brew densitometer, I be a little careful and check the readings it gives you. I've read the nice section on building one in Phil Davis's "Beyond the Zone Sytem" book. Sounds good but has some pitfalls that he talks about. The acid test is to measure a transmission reference with your densitometer and see if it agrees with what another one said. I have a 31 step transmission wedge from Stouffer (http://www.stouffer.net) that I sometimes use to check my densitometer. Pay the extra for them to put the acutal measurements of each step on the sleeve. It's still under $30 for the calibrated step wedge, I think.