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Thread: Reference negative?

  1. #1

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    Reference negative?

    OK, I have finally been convinced to run some really basic film processing tests. I do not have a denistometer and do not indend to invest in one in the near future. However, I do have a good light table, a decent eye and a spot meter. To get a good idea of the density of my negatives, I need some sort of reference negative.

    I was led to believe that Kodak has a B&W wedge reference negative available; actually, I used something like this when I worked in a lab to calibrate our densitometer. Does anybody know the correct number for this, or a source? Or even the correct name so I can at least search for it effectively?

    A related question: The advice for testing seems to run to two camps: Calibrating your process to a known standard (i.e. density) and calibrating your process to your printing process (i.e. getting good prints, sort of calibrating the whole system). I scan. So I wonder if in fact I would be better of in tweaking the processing to achieving better scans, regardless of the absolute densities?

  2. #2

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    Reference negative?

    Hi Paul. I'm a big believer in backwards calibration, because it encompasses your whole system and it works towards your final result, which I find logical and intuitive. Let me first say that I don't know much about scanning, so take my comments with a grain of salt. As I understand it, scannes differ in their ability to read negative densities, probably a function of the intensity of their lightsource, so scaling your negative to fit your scanner should be a lot like scaling it to a particular paper. Obviously, the more density your scanner can read, the longer scale it could read in your negative. I'm sorry I don't know the correct terminology, but I think you can determine the highest density that your scanner can read by scanning your reference negative, or stepwedge, and be careful not to develop your negatives beyond that density. Working backwards, you would find your film speed by identifying the first density above base+fog. The scale that your system will support will lie between those densities. I appologize for my inarticulate terminology, and I hope this makes enough sense to be useful to you. Hopefully someone with a better grasp of the finer points of scanner calibration will reply, and clear things up for you. Good luck.

  3. #3

    Reference negative?

    What you are asking for is called a STEP WEDGE/ It is made at least by Stouffer, and is sold in a few camera shops ( at best a few...).... I suggest... http://www.bostick-sullivan.com/ I tried to pull up Stouffer directly but got a garbage WEB page instead....

    They come in almost every imaginable size and step difference.

  4. #4

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    Reference negative?

    Here's a link to Stouffer's and another option

    http://www.stouffer.net/

    http://www.jnevins.com/stepwedge.htm

  5. #5
    Resident Heretic Bruce Watson's Avatar
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    Reference negative?

    I believe that Frank has your answer for a "reference negative" in the Stouffer step wedge.

    As to your question: I wonder if in fact I would be better of in tweaking the processing to achieving better scans, regardless of the absolute densities? I think the answer is yes, you would, but a negative optimized for scanning is not that much different than a negative optimized for darkroom enlarging.

    My experience in scanning my 4x5 Tri-X negatives is that I get my best results when I calibrate my process to give me negatives just a bit thinner than what you would find to be ideal for enlarger work. That is, a Zone VIII density of about 1.2 in my case. YMMV, you may want to calibrate higher or lower than that based on your needs.

    That said, I'm not worried much about max density since just about any scanner you can name (CCD or PMT) can read through density over 2.0. That is, Zone XI.

    As a result of this realization, I've dropped all N+ and N- development. I develop all my negatives the same way. In other words, I expose solely for the shadows and let the highlights fall where they may. I've been doing this for over a year now. A thousand negatives or more. Some go right on up to Zone XI. Some stop at Zone VI. All scan well, all print well. Of course, YMMV, but this works for me.

    Bruce Watson

  6. #6

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    Reference negative?

    If you scan, you can use Vuescan as a densitometer of sorts. If you press the Ctrl-key, instead of showing you three RGB values, you see corresponding density values. I haven't checked with an actual densitometer how accurate these values are, but they seem pretty consistent with what I would expect. I've checked it against a step wedge I got years ago, and it seems consistent with that. Also, if you scan, you can get some idea of the density range---as measured by Vuescan---that works best for your negatives.

    The RGB values, or course, are pretty useless for this purpose, since the scanning software usually adjusts them so they fit within the range 0..255.

    Many of us use Vuescan (www.hamrick.ocm) and find it very useful.

  7. #7

    Reference negative?

    Paul, Fit your negatives to your scanner's range. Just like fitting your negative to a paper and developer. It will take only a little experimentation to find the exposure and processing that gives you the best results. I find that most times a slightly minus development scans best. The main thing is to avoid a density range that your scanner is not capable of reading. Too thick and you're out of luck. Otherwise if it would print easily in a wet darkroom it will scan well too.

  8. #8

    Reference negative?

    While we're on the subject, exactly how does a step wedge work for calibrating film speed and development? Do you make several exposures of the step wedge at different ISO settings and whichever one prints the dark wedge steps (at your proper proof / maximum black printing time) then that is you film speed rating? Then you expose the wedge several times (at the tested film speed) and develop at different times and whichever development time prints the light wedge steps correctly, then that is the development time you use?

  9. #9

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    Reference negative?

    Thanks for all the help! You are all getting me going on LF much faster then otherwise possible.

    I have been using Vuescan for well over a year (particularly with a Nikon LS 8000), but have actually found that SilverFast AI works very well also (it was included with the Epson 3200). Mind you Silverfast seems kinda buggy. I haven't decided on which one will be my friend just yet

    The step wedges available on Stouffer are pretty much what I am looking for although the steps are a little small (physically) but it should work. The various (and slightly conflicting) advice is very useful. Actually right now I am pretty happy with my results, but then again I am still astounded at the results I have been getting from LF. It really does make you think differently. It is just that I kind of hold my breath every time I develop and a little testing would at least make me more comfortable with the outcome.

    For Mike; it is quite evident I am not the one to answer.

  10. #10

    Reference negative?

    Paul ended his first post: "So I wonder if in fact I would be better of in tweaking the processing to achieving better scans, regardless of the absolute densities?"

    I'm sure that since better scans equal better prints then that is the right answer. Its the print that counts, not the numbers.

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