Step wedge devlopment hep

Discussion in 'B&W: Film, Paper, Chemistry' started by padraigm, Jan 29, 2013.

  1. padraigm

    padraigm Member

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    Hi All,

    Quick question, doing a film test for the first time.

    I have exposed 6 sheets of hp5+ sheet with a stouffer 21 step wedge. Measured EV 4 on the base board. Developed the 1st sheet for 4 minutes(normal 12min published Xtol 1:1). Barely can see anything, got nervous that it is underexposed, so jumped to the development 11min as it is closest to normal fopr a sanity check, and about half are visible. Would I be right is assuming I am at least a stop underexposed and continuing will give me limited information with a densitometer? I figure that you should see most steps at normal..

    Any help would be greatly appreciated.
     
  2. albada

    albada Member

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    Yes, it sounds like the film was underexposed.
    Increasing development-time will show a couple more wedges, but will also make contrast too high.
    Give the film your normal development, and then measure the wedges that have density with the densitometer.
    You'll at least get the left portion of the curve that way.

    Mark Overton
     
  3. bernard_L

    bernard_L Subscriber

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    Can you be a little more explicit and detailed? You exposed HP5+ sheet on the baseboard of your enlarger? How did you determine the exposure? With a light meter? Placed on the baseboard, looking towards the enlarging lens? A light meter normally requires one to set the ISO (ok, 400, or whatever...) and an f-number... but you are measuring in the plane of the film, the light seen by the film, not the light seen by film behind lens, as in a normal situation. I don't understand what exactly you did. When you say EV4, do you mean like 1/2s @ f/2.8? But if you measure at the film location, the f-number is already accounted for as it determines the amount of light as measured.
    That is really short!
    IF you managed to properly meter in the plane of the film (see above remarks) for normal (i.e. zone V) exposure, "half" of the Stouffer wedge should be, IIRC density 1.5, i.e. 5 stops below that, just reaching Zone 0: it is quite normal that the density (above film base+fog) goes down to zero at about that point.
     
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  4. ParkerSmithPhoto

    ParkerSmithPhoto Member

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    Pad, we must be living in parallel worlds, as I am working right now on the same BTZS thing. My exposure time at 2EV for HP5 was 0.9 seconds. (This time may have been a mistake by inviting reciprocity effects.) It took several trials to nail this down, but the sheets look good.

    What you are looking for is an exposure that leaves 20 and 21 clear. This allows you to measure the effects of extended development on the base+fog, which affects your film speed.

    Yes. Just remember each wedge is a half step, so find the one that has some exposure and count up, but be conservative so you don't over shoot it.

    Have you got Plotter yet? There's a demo available. I was a little apprehensive about doing this but I feel now that it will be of great benefit. Incident metering is my preferred way of working, and I shoot a lot of portraits in open shade, so being able to accurately expose these and develop them to the right values should speed things up in the darkroom.
     
  5. ParkerSmithPhoto

    ParkerSmithPhoto Member

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    Pad, one other thing to note is that some meters in EV mode will measure EVs the same regardless of the film speed set on the meter. It's easy to determine if this is the case. If not, your meter must be set at 100.
     
  6. padraigm

    padraigm Member

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    Hi All thank you for the responses. I was following the guideline of having my light meter read EV 4 with .4 of a second pointed up at the enlarger lens. I adjusted the height and f stop to get EV4. I think the mistake I made is that I should have gotten my light meter to read EV2 for 400 speed film. I will try a dew sheets tonight.
    Parker, I have not decided which program to use. I was thinking about the excel sheet from waybeyond monochrome.

    How did your 4 min development look? Are most of the steps blank?

    Thanks
     
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  7. ic-racer

    ic-racer Member

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    You probably want at least 12 points at 0.15 log d apart (as in a 21 step wedge) to make a good H&D curve. Increase the exposure on your enlarger/sensitometer to get there.
     
  8. ParkerSmithPhoto

    ParkerSmithPhoto Member

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    My shortest time was 6 min due to my 1:3 dilution. You should still see density in the 19/20 steps as these are your shadow areas and will develop first. They will increase in density as your dev times increase, but not as much as the highlight areas.

    To get the correct exposure, you are going to have to trial and error it. That's critical if the measurements are to have any meaning.

    I wasted a bunch of sheets to get it right! :blink:
     
  9. Bill Burk

    Bill Burk Subscriber

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    The easy thing about step wedges is that literally each two steps is one stop (assuming a 21-step 0.15 increment wedge). So for every two steps you need to walk to get the last two steps clear, that's how many more stops of light you need.
     
  10. ParkerSmithPhoto

    ParkerSmithPhoto Member

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    My exposure tests with FP4 needed 4.7 EV for 0.5 seconds. I am using a 2 1/4 test wedge, and projecting it onto a 4x5 sheet film holder with a 150mm lens. This leaves 20/21 blank, with just a slight visible density in #19.