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Thread: Film testing

  1. #21
    Michel Hardy-Vallée's Avatar
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    Quote Originally Posted by timbo10ca View Post
    I assume you mean I use a piece of blank paper at a set height, do a test strip series until I see 1st pure black, and then expose the contact sheet at this time?
    Yes.

    Quote Originally Posted by timbo10ca View Post

    Count the number of greys between pure black and white. If you have seven, your dev time is OK.

    you kinda lost me here, unless you are considering zone 1 and zone 9 to be pure black and white, which is what I thought zone 0 and 10 were supposed to be.
    "Zone 1" and "Zone 9" are words for how you interpret your meter reading. If you do not interpret reading, we call it "Zone 5." In a properly calibrated system, when printed on paper, this will look like a grey card. If you augment or reduce your exposure relative to the meter reading, you will get a "zone 3" or a "zone 4" etc., depending on how many stops you add/remove from the reading. Does that make more sense?

    In a properly calibrated system with N development, Zone I is still pure black. Zone 0 is just a way to say "one stop less exposure than Zone I." Likewise, Zone 9 is as white as the paper can be. Zone X is just one stop more exposure than Zone 9.


    Quote Originally Posted by timbo10ca View Post
    If you have six, that's N+. If you have eight, that's N-.

    I'm trying to wrap my head around this one- If there are six greys when you expect seven, that's a contraction (therefore N-), is it not? Vice-versa for 8?
    Nope. Let's say you have seven frames of film corresponding to Zone II to Zone VIII exposure (see explanation above). They are all separated by one f-stop at the moment of exposure. They were "born equal" so to speak.

    When you develop them, they will become seven gradually opaque frames. If your film is developped properly, the least opaque one will print dark grey on paper, and the most opaque will print light grey on paper. That's your seven grays.

    Let's say you have developped for longer than you should have. What's happening is this: the least exposed frames will get a tad darker, perhaps insignificantly so. But the more exposed frames will get proportionally WAY more dark. The ration of opacity between the least and the more opaque will have augmented. The rich get richer while the poor stay put. Just like in real life.

    Ergo, if you have developped too much, the more exposed frames will be too opaque, and will print as pure white on paper, while the least exposed frames will stay more or less the same. Instead of having seven grays, you will have six or five.

    Quote Originally Posted by timbo10ca View Post
    From now on, you can repeat the test a second time if you did not get a first grey on Zone II and seven greys (including Zone II).
    Let's say that the first grey was Zone III, and that you had six greys. That's the likeliest result.
    You're going to set your meter to 200 instead of 400, shoot the same sequence, and develop for 20% less than 8 mins (~6 mins), and do the contact sheet again.


    You mean, repeat this test until you get your proper film speed and normal development for that speed? Suppose you determine this, how do you then determine what N+ and N- are?
    Yes. N+ is a pair (dev time; EI), N- is a pair (dev time; EI). For example, my N is (6 mins; 200), my N+ is (8 mins; 400) and my N- is (4 mins; 100).

    My N means:
    * My meter is set at 200
    * The frame that I expose at Zone II is the first grey on the contact
    * I have 7 distinct greys (zone II to zone VIII) on the contact

    My N+ means:
    * My meter is set at 400
    * The frame that I expose at Zone II is the first grey on the contact
    * I have 6 distinct greys (zone II to zone VII) on the contact

    My N- means:
    * My meter is set at 100
    * The frame that I expose at Zone II is the first grey on the contact
    * I have 8 distinct greys (zone II to zone IX) on the contact

    I hope I'm not making this more complicated for you!
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  2. #22
    timbo10ca's Avatar
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    Quote Originally Posted by mhv View Post
    Yes.



    "Zone 1" and "Zone 9" are words for how you interpret your meter reading. If you do not interpret reading, we call it "Zone 5." In a properly calibrated system, when printed on paper, this will look like a grey card. If you augment or reduce your exposure relative to the meter reading, you will get a "zone 3" or a "zone 4" etc., depending on how many stops you add/remove from the reading. Does that make more sense?

    In a properly calibrated system with N development, Zone I is still pure black. Zone 0 is just a way to say "one stop less exposure than Zone I." Likewise, Zone 9 is as white as the paper can be. Zone X is just one stop more exposure than Zone 9.




    Nope. Let's say you have seven frames of film corresponding to Zone II to Zone VIII exposure (see explanation above). They are all separated by one f-stop at the moment of exposure. They were "born equal" so to speak.

    When you develop them, they will become seven gradually opaque frames. If your film is developped properly, the least opaque one will print dark grey on paper, and the most opaque will print light grey on paper. That's your seven grays.

    Let's say you have developped for longer than you should have. What's happening is this: the least exposed frames will get a tad darker, perhaps insignificantly so. But the more exposed frames will get proportionally WAY more dark. The ration of opacity between the least and the more opaque will have augmented. The rich get richer while the poor stay put. Just like in real life.

    Ergo, if you have developped too much, the more exposed frames will be too opaque, and will print as pure white on paper, while the least exposed frames will stay more or less the same. Instead of having seven grays, you will have six or five.



    Yes. N+ is a pair (dev time; EI), N- is a pair (dev time; EI). For example, my N is (6 mins; 200), my N+ is (8 mins; 400) and my N- is (4 mins; 100).

    My N means:
    * My meter is set at 200
    * The frame that I expose at Zone II is the first grey on the contact
    * I have 7 distinct greys (zone II to zone VIII) on the contact

    My N+ means:
    * My meter is set at 400
    * The frame that I expose at Zone II is the first grey on the contact
    * I have 6 distinct greys (zone II to zone VII) on the contact

    My N- means:
    * My meter is set at 100
    * The frame that I expose at Zone II is the first grey on the contact
    * I have 8 distinct greys (zone II to zone IX) on the contact

    I hope I'm not making this more complicated for you!
    This is becoming more and more clear to me- thanks alot. I'm just wondering how you are making these N, N-, and N+ pairs. By increasing one variable and decreasing the other, doesn't the outcome stay equal (I'm thinking in linear relationships here to keep it simple in my mind). I thought your N+ and N- were development times you applied to a single, unchaging EI/film iso rating.
    Also, what is the f/stop and time combo you mentioned earlier for the test frames?

    Thanks,
    Tim
    Last edited by timbo10ca; 02-08-2007 at 05:56 PM. Click to view previous post history.
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    Quote Originally Posted by timbo10ca View Post
    I am in the process of trying to do some film tests according to the Zone System in 35mm. I think understand the concept - Find the correct film speed that gives you detail in Zone 3, then find the development time that gives you good detail in Zone 8. Then it all got turned on its ear when I was reading a thread at P.net and someone mentioned Barry Thornton's "Edge Of Darkness". He sais that for depending on the brightness of the scene, rate the film at box ISO (cloudy, no shadows) and develop as recommended, and to rate the film at 1/2 box iso and decrease development by something like 20-30% (bright sun, sharp shadows). I thought that film testing was to give you the film's speed, regardless of the light outside! Is his vernacular just another way of deciding on exposure and N minus development for scenes that have a long exposure gradient for "non-zonies"? I'm trying to wrap my head around his use of box ISO for cloudy scenes and normal development though. It seems that film is always slower than its box ISO.....

    Thanks again,
    Tim
    i have read some of this 'high tech' stuff on exposure, they make it unnecessarily complicated especially for negative exposure

    but i know from experience box iso is probably calculated for nice soft light, so if my subject and scene is illuminated by soft light (not often outdoors in Australia) then i set manufacturers recommended ISO (who am i to argue with the experts) and process as recommended with a 'normal' developer

    if my lighting situation is contrasty i set half ISO and reduce dev time by 30%

    in all cases i meter off something middish toned that is getting the same light as my subject/focal point and use that setting

    it doesn't have to be rocket science, making it complicated and high tech doesn't make it better

  4. #24
    Michel Hardy-Vallée's Avatar
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    Quote Originally Posted by timbo10ca View Post
    This is becoming more and more clear to me- thanks alot. I'm just wondering how you are making these N, N-, and N+ pairs. By increasing one variable and decreasing the other, doesn't the outcome stay equal (I'm thinking in linear relationships here to keep it simple in my mind). I thought your N+ and N- were development times you applied to a single, unchaging EI/film iso rating.
    Also, what is the f/stop and time combo you mentioned earlier for the test frames?

    Thanks,
    Tim
    Tim, the first thing to understand about film testing is that nothing is linear. Development effects densities unequally. You're always doubling or halving the quantity of light. There is a discrete step between unexposed film and minimal exposure, not a continuous one, etc.

    If you increase exposure and reduce development, that's not doing the same thing as reducing exposure and increasing development. The reason lies in the fact that development impacts highlights in a different way than it impacts the shadows.

    The nature of the reaction of photosensitive emulsions (film and paper) to light is the single most fundamental thing to grasp. It's because of its characteristics that what seems to be equivalent operations are not. You should probably get some graphics of a characteristic curve to help you.

    At this point, I guess if you want to know the WHY rather than the HOW, you need to get a textbook like Ansel Adam's The Negative (the last editions are way more readable than the earlier ones).

    The reason why the EI is different between the N, N+ and N- is twofold: first, because development also effects slightly film speed, as I've said in an earlier post. But that's just a minor correction, sometimes half to a third of a stop. The real reason is because that's how you control the contrast.

    Let's say you have a scene. A portrait in the sun, light diffused from a lightly overcast sky. The light comes from the left side of your subject. Her left side is brighter than her right side because of this. You meter her left side and her right side. There's a difference of one stop. If you expose and develop your film normally, there will be a difference of one stop on the final print. You have exposed and processed for N, and thus you did not alter the contrast of the scene.

    Let's say you expose it less than in the previous case. What it does is that overall, the photo will be darker, right? You have slightly underexposed. Both sides will be darker, but will bear the same relationship to each other: one stop of difference.

    But let's say that on top of that you develop more. THAT's where the magic begins. The darker side will stay dark, but the brighter side will be three stops brighter than the darker side on the negative, and on the print you will also see this difference. You will have a portrait with more contrast. You have exposed and developed for N+, and you have augmented the contrast of the scene.
    Using film since before it was hip.


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  5. #25
    Steve Smith's Avatar
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    Quote Originally Posted by Roger Hicks View Post
    The science of exposure is nothing like as exact as most people assume, and there's a lot of latitude you can fix in the darkroom.
    Whilst I agree with this, generally it seems that in camera exposure is seen as an exact science whereas darkroom exposure is seen as more of an art when, in fact, both should be equally predictable.

    I am going to do an experiment the next time I am in the darkroom (hopefully this weekend).

    I am going to select a negative then put it in the enlarger and compose and focus it. Then I am going to remove the negative and replace it with a blank piece of film from the same roll and do a test strip to find minimum time for maximum black.

    I will then replace the negative and expose for this time. If the negative was exposed and processed correctly, I should have a good print (assuming grade 2 to 3 filtration).

    If it is too dark, then the natural instinct to reduce the exposure time will obviously not work as I would not then get maximum black. An increase in grade will be required.

    I will post my results if they are of any interest.

    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

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    Quote Originally Posted by Steve Smith View Post
    Then I am going to remove the negative and replace it with a blank piece of film from the same roll and do a test strip to find minimum time for maximum black.

    I will then replace the negative and expose for this time. If the negative was exposed and processed correctly, I should have a good print (assuming grade 2 to 3 filtration).
    Dear Steve,

    I'm not convinced by this, as it assumes zero density (above fb+f) somewhere in the 'real' negative, which can by no means be taken for granted. Even if it could, how much use is it?

    Like many people, I prefer generous exposure for three reasons. First, the tonality is often better. Second, I'd rather have detail and throw it away if I don't want to print it, rather than not have it there if I do want it. Third, the tolerance in B+W photography is much greater for over-exposure than for under-exposure, so it makes sense to err on the side of over-exposure if you're going to err at all -- though of course over-exposure means bigger grain and reduced sharpness, so you don't want to go too far.

    My own preference is for basing exposure on a shadow reading of the darkest area in which I want texure: about 2-1/3 to 2-2/3 stops less than the reading taken using the true ISO of the film in the developer I am using.

    Basing exposures on true ISO speeds and shadow readings saves a lot of tedious and (for most people) unnecessary speed testing, because, after all, shadow readings (toe speed) are what ISO speeds are based on. I normally take the box speed as the true ISO in D76/ID-11, and reckon on +2/3 stops in DD-X or DD-X or Microphen and -2/3 stop in Perceptol. There is seldom any need for greater precision than this.

    Please (this isn't directed at you, Steve, but at those who don't actually understand what ISO speeds are) don't tell me that box speeds aren't true ISO. Even with Fomapan 200, they are, though you have to read the spec sheets to see that Foma 200 is only 200 in speed increasing developers, and that only by courtesy; its true ISO in just about everything matches that of FP4 Plus, viz. 80-180 or so.

    If you use any metering technique other than shadow readings, such as pissing around with 'mid-tone' grey card readings, or if you grievously curtail development, no-one can predict what personal EI will work best. With through-lens meters on a sunny day, for example, I'll normally set an EI that is 2/3 stop or even 1 stop lower than the true ISO, or 'interpret' the reading according to the subject.

    Cheers,

    R.
    Last edited by Roger Hicks; 02-09-2007 at 06:10 AM. Click to view previous post history.

  7. #27
    Steve Smith's Avatar
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    Quote Originally Posted by Roger Hicks View Post
    Dear Steve,

    I'm not convinced by this, as it assumes zero density (above fb+f) somewhere in the 'real' negative, which can by no means be taken for granted. Even if it could, how much use is it?
    I'm not sure that I'm convinced either but I'm going to try it anyway!

    Like you, I tend to go for plenty of exposure. Reading various articles on finding your 'personal film speed' I see that most of these tests end up with an EI rating around half that of the film's ISO i.e. twice the exposure that you would get with using the ISO setting.

    With that in mind, an extra stop of exposure is probably a fairly good rule of thumb whether you have done your personal tests or not.

    As for my darkroom experiment, it it just that - an experiment because I am currently in an experimental mood!

    It just seems to me that when we meter a scene we can use the ISO or EI and our meter readings to set up the camera with a fairly predictable idea of how the image will appear on the film without having to do the equivalent of a test strip on a piece of film before taking the actual image. But when it comes to the darkroom it is a bit more hit and miss. I think there could be a more logical method. I suppose that's what those enlarger lightmeters I can't afford are for!

    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  8. #28
    Michel Hardy-Vallée's Avatar
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    Quote Originally Posted by Steve Smith View Post
    But when it comes to the darkroom it is a bit more hit and miss. I think there could be a more logical method. I suppose that's what those enlarger lightmeters I can't afford are for!

    Steve.
    I've noticed that when I have film that is properly exposed, I am generally in the same ballpark for printing every frame. Sometimes when I want a quick proof I just print the shots I want at 13s, 8x10, f5.6, and that's enough to give me a sense of whether I like the photo or not.

    Your test for minimal time for max black by projection through fb+f is the same thing as what one does with a contact sheet (the "proper proof" in Picker-talk). But that means that overexposed photos will look just like that, overexposed. That's why you need a contact sheet to know first which frames are over/under.

    A lot of pissing around in printing goes away with a properly calibrated system and a good technique. For my setup, I make most straight prints with times between 10s and 20s. I learned by heart the f-stop sequence: 8, 10, 12, 14, 17, 20, 24; and I go up or down this scale to nail my straight exposure. After that it's dodge and burn, but that's something you can't exactly predict because you use it creatively.
    Using film since before it was hip.


    "One of the most singular characters of the hyposulphites, is the property their solutions possess of dissolving muriate of silver and retaining it in considerable quantity in permanent solution" — Sir John Frederick William Herschel, "On the Hyposulphurous Acid and its Compounds." The Edinburgh Philosophical Journal, Vol. 1 (8 Jan. 1819): 8-29. p. 11

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  9. #29

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    Quote Originally Posted by Steve Smith View Post
    With that in mind, an extra stop of exposure is probably a fairly good rule of thumb whether you have done your personal tests or not.
    Dear Steve,

    Probably so, but I can't help feeling than an awful lot of it is down to poor metering technique, i.e. not using a spot meter to read the shadows, which is the ONLY way to ensure adequate shadow exposure and no more. People who refuse to meter this way (usually on the grounds of convenience -- I do not exempt myself) have to build in 'fudge factors' which, as you say, are typically around one stop. With a spot meter, you can afford to be quite a bit closer to the ISO speed.

    Cheers,

    R.

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    Timbo10CA
    Many want your way to use zone system with 35 mm and just gave up saying it does not works with 35mm.
    It works in just any format. But take care.

    What film area is smaller the more accurate you have to be for the same result. Spot meter (around 1 deg) will be a great helper. So learn with time and concetrate on accuray (exposure, developer temperature, developing time, film speed,...).
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