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  1. #11
    DJGainer's Avatar
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    Quote Originally Posted by AlanC View Post
    Halving film speed has nothing to do with shadow detail or highlight detail. In a high contrast situation you cut down development time to keep the highlights under control. This can have the adverse effect of lowering the mid-tone values in the final print. "Overexposing " the film by one stop pushes these mid-tone values back up to where you want them. This is the reason for halving the film speed. Ansel Adams explained all this a long time ago....

    Alan Clark
    I wasn't saying that you cut your exposure for the shadow detail, only that the shadow detail is affected if your development time remains the same. So you start with a standard development time, shoot at a few different speeds, pick the frame you like the best (based on shadow detail), use that EI, then vary development until your highlights come out as you want.

  2. #12
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    Of course all of this depends on how you use your meter as well. For example, if you take an average reading of a scene on an overcast day (careful to avoid too much sky - light source - influence) you may have normal or even slightly dense shadows. The same reading taken on a bright sunny day will tend to rob your shadow areas of exposure. This is why the old timers (and further developed by Adams) maintained that you'd best expose for the shadows and develop for the highlights.

    Since our ISO setting refers to the response of the film to the regions in which there is least light, that's where the readings need to be taken if you wish the results to be rational. The problem with the bright scene is that the average is so much higher, that the dark areas really aren't considered, and tend to be underexposed. In taking the readings in the shadows, we would not want to read the meter in the same way as we would if we were taking an average reading. We must account for the fact that shadows really are dark. So in practice, we'd cut our shutter speed by two stops OR close the aperture down by two stops, or one stop of each, or whatever equivalent to that one might prefer. That would be the same as placing the general shadow reading at zone 3. I do this regardless of whether the day is overcast or not. Some people may prefer to cut the exposure from the reading a bit less.

    So the point: Yes, 1/2 the box speed is a great place to start. That is where I start when I test a film. But, if you follow the reasoning above, I think you can see that even in using the slower speed, there may still be times when you underexpose with a general average reading, especially on bright scenes. Cutting the speed in half is just one stop; the full range of brightnesses could average more than one stop too high. Conversely, cutting the speed might be just right on Groundhog Day, or it might be too much.

    In short: I strongly suggest that you devote a bit of time, film, chemistry, and energy to performing a series of tests.

  3. #13
    2F/2F's Avatar
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    Why did you decide to start exposing your film at EI 200? Blindly half rating one's film is usually a shortcut rule of thumb given to chronic underexposers, rather than taking the time to teach them how to meter properly. Assuming you know how to get a good exposure using your light meter, this should not be necessary unless something is wrong with your meter, shutter or aperture. If you deliberately want to shift everything one "stop" upward on the film's characteristic curve across the board without having to think about it, that is another reason. However, this is not why most people half rate, and I think it makes more sense to do this shot by shot via manual overexposure than by rerating your film. It should not be necessary if you are looking for "normal" exposures. If you find this opens up your shadows to a tone that you like, have at it, but you might want to experiment with 15 to 25 percent underdevelopment to tame the high end if you are shooting in contrasty light.

    The main idea is that you cannot judge your exposures until you know for sure that you understand metering.
    Last edited by 2F/2F; 04-02-2009 at 01:47 PM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

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  4. #14
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    2F/2F -- I think the whole point is that setting one's ASA by what is on the box is as "blind" as setting it 1/2 the box ASA.

    bowzart -- thanks, I have been using a spot meter for so long that I tend to forget that most people take "average" readings!
    At least with LF landscape, a bad day of photography can still be a good day of exercise.

  5. #15
    OMU
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    hi,
    Yesterday I finished my testing of FP4+ in HC and my E.I. is 80 with dilution B of HC-110. I use JOBO, 20 C.

    That is of course different from HP5+.
    I'll start testing HP5+ in HC-110 this weekend and expect an E.I. somewhere between 400 and 200 ASA.

  6. #16
    2F/2F's Avatar
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    Quote Originally Posted by Vaughn View Post
    2F/2F -- I think the whole point is that setting one's ASA by what is on the box is as "blind" as setting it 1/2 the box ASA.

    bowzart -- thanks, I have been using a spot meter for so long that I tend to forget that most people take "average" readings!
    Hi,

    By "blindly half rating" I simply mean using blanket overexposure as a quick fix to cure poor exposures, as opposed to testing in order to discover exact personal discrepancies with box speed.

    I have to disagree that using a half rating is just as blind as using box speed. (I agree that box speed often does not work as well as another EI, however.) I would argue that most who meter "average" scenes with in camera meters will get better results at box speed than at a half rate. The thing is that averaging meters are not designed to give you the best exposure, but, rather, an exposure that will allow a decent ("average") print to be made in a decent percentage of situations. This is generally acceptable to most people, IMO, and makes plenty of sense to me. Rules of thumb like half rating skew these "please the masses" results, however, favoring one sort of shot while sacrificing another to do it. Using half rating to cure weak shadows hurts just as many shots as it helps, IMO, because some situations benefit, while others do not. Better off being "average and decent most of the time" than right on sometimes and way off others. It's a "shotgun" approach IMO, and is *usually* (not always) suggested by people who don't care to, or are too lazy to explain things fully to a beginning student, and/or by people who have come to rely on these methods themselves. If you are going to half rate or double rate in the most successful way for all pictures, you should do it based on the contrast of the individual composition to make it work, IMO; not as a total blanket approach to fixing exposure issues.

    You are just as likely to shoot at box speed as you are to shoot at half of it, IMO...and more likely than *either* to shoot at *neither*. (I even shoot *over* box speed on one film when using the zone system, and routinely shoot over or under box speed when using an incident meter, based on my desired contrast. Most commonly, this involves HP5 at 500, 1000, or 250, or Delta 1000 at 2000 or 4000.) Which EI works for you largely depends on how you determine a "working" EI. E.g. Do you want to use a zone I density to determine your EI, or another zone such as II or III, or no zones at all and do it by eye? What paper do you use? What does your eye call a "proper" shadow density? It's up to you, and thus working EIs can be all over the map depending on your methods and desires.

    Because of this, a "blind" half rating can have varied results. For some examples from the films I have "calibrated", I shoot FP4 at 200, *and* TXP at 200, Pan F at 16, and HP5 at 400 (based on a 0.40 above FB+F density AKA the forward edge of a zone II density). With the Tri-X, a blind half rate of its 320 box speed would only overexpose by 1/3 stop. Not bad. Not ideal, but a bit better than using box speed. With FP4, a half rate (of its 125 box speed) would cause a 1-2/3 stop overexposure, while box speed would cause a 2/3 stop overexposure. Box speed would be workable, but not the best to work with, and a half rate of box speed (EI 64) would be difficult to print, IMO. With Pan F, half rating would give me a 2/3 stop underexposure. Better than box speed, for sure, but still too dark in the shadows. With HP5, half rating would give me a 1 stop overexposure. Better off with box speed in this case. The amount of variation makes the application of a rule of thumb likely to cause many wonky results as well.

    The real issue is learning how to meter and place tones. You don't need to go crazy with the zone system or anything, but until you know how to do that well at box speed, you will have a hard time even judging whether or not the box speed is working for you. My gut opinion is that anyone firing shotguns at exposure problems needs to take a step back and examine things a bit more carefully before resorting to rules of thumb. There are no quick fixes or magic bullets.
    Last edited by 2F/2F; 04-03-2009 at 04:59 AM. Click to view previous post history.
    2F/2F

    "Truth and love are my law and worship. Form and conscience are my manifestation and guide. Nature and peace are my shelter and companions. Order is my attitude. Beauty and perfection are my attack."

    - Rob Tyner (1944 - 1991)

  7. #17

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    Perhaps we have been talking at cross purposes here, probably because I made a wrong assumption in my earlier post. I should have said "once you have determined your own personal film speed you should expose at half this speed in a high contrast situation" The reasons for this are given in my earlier post.

    I agree that if you have done no film speed testing, halving box speed-in any situation- is a handy practical thing to do, especially with 35mm when the film may be exposed in a variety of lighting situations. But it is better to do some simple tests.

    Alan Clark
    Last edited by AlanC; 04-03-2009 at 04:27 AM. Click to view previous post history. Reason: Adding to post

  8. #18
    Steve Smith's Avatar
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    My normal HP5+ regime is EI 200 and develop for 75% of the ISO 400 time for whichever developer I am using.



    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.

  9. #19

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    My "normal" regime for HP5+ is to rate it at 400 and develop for 20 min in ID11 1 + 3.
    In sunny conditions - "normal minus 1" I rate it at 200 and cut down development to 15 min

    Alan Clark

  10. #20
    Steve Smith's Avatar
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    Quote Originally Posted by 2F/2F View Post
    I have to disagree that using a half rating is just as blind as using box speed.
    I disagree too.

    When I first heard about finding your true film speed, etc, I did a lot of research and almost every article I read which documented a lot of tedious testing of multiple frames at various exposures and then developing for varying times came to the conclusion that halving the box speed and reducing development was the best method.

    I could have replicated these tests for myself but I chose not too. Instead I shot a roll of HP5+ at EI 200, gave it 75% of normal development and printed some pictures.

    I decided that I liked it and have carried on this way ever since. The only time I use HP5+ at ISO 400 is on quite dull days.


    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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