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Thread: Film Test

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    Film Test

    I am carrying out film test with the help of Stauffer's 35-21projection step wedge. I shall put the wedge in slide duplicator and expose the film the same way as duplicating a slide.The aperture in the duplicator is fixed-i.e.16. However, the exposure- under/over can be controlled through the camera by means of exposure compensation. I would like to know as to how I expose th e film i.e. normally or under/ over expose for the purpose of evaluating the film speed ?

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    how are you metering? I've never used a slide duplicator...
    the other thing is - what film - what lens - what developer - what kind of light (back to what film) -

    When I used my step wedge for speed tests, I picked a band on the wedge, metered using a spot meter, and exposed for that lowest tone to register as something above film base + fog. I then started taking pics with the exposure for the box rated film speed, then slower, then slower (ASA's) . Take the several films to the development, and the one that gives the first hint of tone above b+f is your working film speed.... it usu. won't be the "box speed". . ..

    The way I do things is by no means "the way" it's just " a way" . .. .

    To help you more we need to know what film, at least. The next issue I would consider is that the speed rating you give your film would "technicaly" only be valid for that particular setup (camera+lens+film+dev) . . . .

    More info Please.

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    The film is Kodak T max, the lens 35/70 zoom and the developer D-76. The step wedge is projection type-meant for using in 35mm enlarger. The spot meter reading of a band of grey from this small wedge may not be possible.By exposing the film to be tested through the duplicator, I am copying the wedge on the film and then assessing as to how may bands of grey are recorded.

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    Quote Originally Posted by Hansraj Vyas
    I am carrying out film test with the help of Stauffer's 35-21projection step wedge. I shall put the wedge in slide duplicator and expose the film the same way as duplicating a slide.The aperture in the duplicator is fixed-i.e.16. However, the exposure- under/over can be controlled through the camera by means of exposure compensation. I would like to know as to how I expose th e film i.e. normally or under/ over expose for the purpose of evaluating the film speed ?
    Can you take an incident reading from the exposing unit. If you can, use the exposure time that gives you 4 EV.

    If not, then I would start with an exposure of about .3 sec at f/16.

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    well....
    you could always project the step wedge, and spot meter the projected bands... then drop the meter reading by three stops (when metering the darkest band) and start exposing.. like Jay said, start at the box speed, then start dropping it in 1/2 or 1/3 stop increments... develop normaly. the first neg to show you something above the blank film base + fog is your actual ASA

    OR-
    ditch the step wedge, pick a suitably dark subject, and start exposing ... lowering your ASA as you go... develop... the one that gives you some detail in the dark parts is your ASA...

    I am copying the wedge on the film and then assessing as to how may bands of grey are recorded.
    well that will tell you how wide a range your film can register... but it wont tell you dirrectly your ASA. If you over expose the film you should see more bands farther and farther into the deep tones of the wedge.. if you underexpose the film you will see more and more steps towards the light tones of the wedge... either way, you are likely to count about 15 steps... maybe as few as 11 if you grossly over/under expose.
    BUT, as you are not gettting specific information about the value of some particular step, you cannot extrapolate ASA... ASA will be tied to the exposure value of any particular band.

    There is another thought - let's assume that your copy machine is designed to give you "average" exposure, rendering Zone V subjects as Zone V on your negatives... let's just assume that...
    You could expose your T-Max at several ASA values, and use the one that (on the neg) gives you as many bands above the middle step (step 11 on a 21 step wedge) as below it... that way, you would (presumably) be exposing and getting zone V for zone V . . ..

    um . .. nope... there is one problem with that... exposure relates how much light is needed to register the faintest bit on your neg..... and how long you develop will affect how dense all your tones are.. but least of which your faintest tones... those that would represent the Zone 3 exposure for a given band in your step wedge... so again, you need to know what the "correct exposure" (middle gray) for a given band would be, and then drop the exposure by two stops...

    OK.. so here is another thought..
    Your machince is supposed to render zone V subjects as zone V. right?
    So - figure out what the normal exposure is . ..
    drop down two f/stops. now your zone V step on the tablet SHOULD register as just a very faint zone III. . . .. expose for that ASA. . . repeat for lower ASA's . .. develop.. the neg that just barely shows you the middle gray, zone V, step on the wedge (#11) is your ASA. . ..

    I'd like it if someone else came along and stewed on this for a bit.... two noodles are better than just one...

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    I use Kodak T max 35mm film and D76 film developer. The slide duplicator has a lens with fixed aperture of 16. It is attached to the camera body like any other lens. The duplicator has a stage where the step wedge is placed. Holding camera with attached duplicator against light, the exposure is made. Exposure control can be done through camera's exposure compensation. The exposed film is thus a copy of the wedge and depending upon the grey bands recorded, an assessment of the film speed may be made.Spot meter reading of this small wedge may not be possible.

  7. #7
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    Spot meter reading of this small wedge may not be possible.
    Right.
    But you cannot also rate your film without knowing how bright any particular band is.
    Your duplicator gives you f/16. OK. So you can adjust exposure with shutter speed. OK. The problem is you MUST know at least ONE specific luminance value for ONE specific band/step. It is by placing a particular tone at the threshold of your film, that you "rate" it. The only way you can place a particular value at the threshold of your film, is by knowing how long the film must be exposed to it to give you a "normal" exposure, and then reducing your exposure by two steps...

    If we go back to the assumption that the overall meter reading of the step tablet will give you a real zone V at step # 11, then all you have to do is reduce your exposure by two stops, to place it at zone III, and shoot. As you increase exposure in the next shots, you will be lowering your ASA, which will cause the camera to "see" darker and darker tones on the step wedge. When the film first shows tone in the #11 step, you are looking at zone V, two steps down... at the threshold of your film. You would have then rated your film. THEN, once you have a film rating, you could meter your tablet (in camera, average metering for the entire tablet) and shoot the film at the ASA you determined. It should place step 11 at the center of all the visible bands.

    I hope this helps Hansraj... I'm sure there are quicker ways of doing the speed testing... but ultimately, you will have to navigate the variables with the istruments you have at hand, and find your own way. I don not, however, believe that you can carefully asign an ASA without being able to meter for a particular tone. The only way around this, I believe, is to assume that your camera will meter the step wedge, and choose an "average" meter reading, which SHOULD place step 11 at the middle of the scale, on Zone V.

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    Film Speed

    Yes, Mr.Huber, You are right. Unless a reading is taken, it would not be possible to find ASA. In fact, in the past, following Fred Picker's method I could find the effective speed of the film. However since Stauffer's wedge was with me I though of experimenting with it. I thank you and others for valuable inputs. Hansraj.



 

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