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Thread: Help a noob understand the exposure conundrum

  1. #11

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by jp View Post
    If the shutter wasn't meant for that lens, the f-stop calibration is useless. This is compounded by the difference in f-stop units historically.
    Could your lens have an iris or studio shutter that's stopped down even though your separate shutter is wide open? Or waterhouse stop needing to be removed?
    The lens has its iris which is wide open at 6.8. The shutter also is wide open, at 1.9.

    The lens focuses at what looks like around 14" (no tape measure till morning) which is way bigger than the Mamiya can open out to. I only mentioned the Mamiya cos the 6x6 must be approx 1/8th the size of the 5x7. It isn't the same lens, one is Mamiya the other on the LF is the wray

    I'll measure and run the formulas in the morning.

    It's not development. I can run a decent neg, it's something about the camera/lens/shutter combo.

  2. #12
    Jim Jones's Avatar
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    Re: Help a noob understand the exposure conundrum

    The U. S. system of marking apertures was invented to simplify [?] exposure calculations. The numbers double for each halving the exposure. U.S. 1 + f/4, U.S. 2 = f/5.6, U.S. 4 = f/8, U.S. 8 = f/11, U. S. 16 = f/16, U.S. 32 = f/22, U. S. 64 = f/32, U.S. 128 = f/32, and U.S. 256 = f/64.

  3. #13

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by jp View Post
    It could be the film is loaded facing the wrong way.
    Could be ........Ilford hp5, grooves in top right corner with film held in right hand has the emulsion facing me? Correct?

  4. #14

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by Jim Jones View Post
    The U. S. system of marking apertures was invented to simplify [?] exposure calculations. The numbers double for each halving the exposure. U.S. 1 + f/4, U.S. 2 = f/5.6, U.S. 4 = f/8, U.S. 8 = f/11, U. S. 16 = f/16, U.S. 32 = f/22, U. S. 64 = f/32, U.S. 128 = f/32, and U.S. 256 = f/64.
    The shutter is wide open, showing 1.9. As the English lens only opens to 6.8, this should be the limiting factor?

    I started by going with what the Weston said -1/250th at 6.8 and got virtually nothing on the neg. only when I increased it in steps up to 1 sec did I get good density. Development was held the same - rodinal 1:50 at 20 degrees c for five minutes. All I did all through the 'tests' was increase the exposure time from 1/250th to 1 sec.

  5. #15

    Re: Help a noob understand the exposure conundrum

    Is it a Telemetric or Telecentric? A shutter like that marked 1.9 would probably have contained a short oscilloscope lens. It's possible that the clear area of the shutter wide open is smaller than the clear area of your lens wide open. There is also the possibility of mechanical vignetting I suppose. When you look through the front glass of the lens when it is on the shutter and measure the opening you see in mm and divide that into 300 what do you get?

  6. #16

    Re: Help a noob understand the exposure conundrum

    Also Rodinal 1 to 50 for 5 minutes for HP5 sounds kind of short. I think my time is 12 minutes.

  7. #17

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by Chauncey Walden View Post
    Also Rodinal 1 to 50 for 5 minutes for HP5 sounds kind of short. I think my time is 12 minutes.
    Oops 1:25, my mistake. 4.75mins - off the Massive development chart. Yes 1:50 would be 10-13 mins.

  8. #18

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by Chauncey Walden View Post
    Is it a Telemetric or Telecentric? A shutter like that marked 1.9 would probably have contained a short oscilloscope lens. It's possible that the clear area of the shutter wide open is smaller than the clear area of your lens wide open. There is also the possibility of mechanical vignetting I suppose. When you look through the front glass of the lens when it is on the shutter and measure the opening you see in mm and divide that into 300 what do you get?
    1.9 is the shutter iris. The lens has a 6.8 iris. I'll measure in the morning. I just get the 5x7 covered, no real room for movements.

  9. #19

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by Chauncey Walden View Post
    It's possible that the clear area of the shutter wide open is smaller than the clear area of your lens wide open.
    I second this. Just looking a an image of the shutter, the opening looks quite small for a 300mm f6.8 lens. For example, the 300mm f5.6 Symmar-S takes a Copal No. 3. Just a guess.
    Last edited by faberryman; 3-Sep-2017 at 07:38.

  10. #20

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    Re: Help a noob understand the exposure conundrum

    Good point, Frank. The OP says he has a #3 Elgeet shutter. Its an Ilex #3 Universal rebadged for Elgeet, who made the lens that was originally in it. Most likely taken from an oscilloscope camera.

    Normal Ilex 3s open to 35 mm. Many 'scope camera Ilex 3s for f/1.9 lenses have restricted apertures, open to around 30 mm.

    OP, a shutter's aperture scale ia for the lens intended to be mounted in it. From all other lenses' points of view, totally arbitrary and incorrect numbers. Oh, and by the way, when you took y'r shots the shutter's diaphragm should have been wide open. Was it?

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