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Thread: Help a noob understand the exposure conundrum

  1. #21
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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by TimberwolfII View Post
    Could be ........Ilford hp5, grooves in top right corner with film held in right hand has the emulsion facing me? Correct?
    Correct.

  2. #22

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by Dan Fromm View Post
    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?
    Awake early for a Sunday and had tape measure out. The aperture in the Ross lens is 25mm at 6.8 on the dial - wide open; the shutter is 26mm at 1.9 - wide open. Both were wide open when making all the shots, I only changed the one variable whilst searching for the neg density - shutter speed. Also no bellows extension, I left it where it was focused when I brought it in - near as makes no odds 300mm lens iris to ground glass.

    So, is my lense with a circa 30mm dia overall and an iris that opens to 25mm able to transmit less light that a massive aero Ekta say which is physically five times bigger? Or do they go to 2.8, 1.9 etc and have a greater aperture to focal length ratio?

    Still not much idea as to where my 8 stops of light has gone!! Lots of head scratching from all you kind folk for which I'm very grateful!

    Is it because I have a dinky little lense with a dinky little hole that only lets in a glimmer of light for that big ol 5x7, and just live with it darn it!?

  3. #23

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    Re: Help a noob understand the exposure conundrum

    A picture of your camera and lens might be worth a thousand words. Did you ever look inside the camera to make sure there is not a color gel inside or a filter on the back of the lens? Is your subject 14 inches or your bellows length 14inches when focused? Is it possible your medium format camera shutter is off by a couple of stops too?

    Try a different lens or have your lens tested, meter with a phone App to compare meter results. Does your meter have low light and daylight settings (like the leica meters) ?

    You have to eliminate one variable at a time.
    The mountain waters of North Georgia call out to me, I visit and leave only tripod holes behind. The Appalachian Trail is my treadmill and gym.
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  4. #24

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by TimberwolfII View Post
    Also no bellows extension, I left it where it was focused when I brought it in - near as makes no odds 300mm lens iris to ground glass.
    Arrgh!

    Ross didn't make a "Telemetric." They made a telephoto lens called Telecentric.

    300/6.8 = 44, not the 25 you measured.

    You have a telephoto lens. The rear nodal point, from which extension is measured, is far in front of the diaphragm.

    You have a telephoto lens. It has considerable pupillary magnification. The f/ number is calculated as focal length/diameter of the entrance pupil. Measure the entrance pupil, not the diaphragm.

    There are books on LF photography. The two most commonly recommended here are Leslie Stroebel's View Camera Technique and Steve Simmons' Understanding the View Camera. Both available used at low prices from on-line booksellers, e.g., abebooks.com, alibris.com, amazon.com, bn.com, ... Buy one and study it. You'll learn more that way than from short random answers to random questions.

  5. #25

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by esearing View Post
    A picture of your camera and lens might be worth a thousand words. Did you ever look inside the camera to make sure there is not a color gel inside or a filter on the back of the lens? Is your subject 14 inches or your bellows length 14inches when focused? Is it possible your medium format camera shutter is off by a couple of stops too?

    Try a different lens or have your lens tested, meter with a phone App to compare meter results. Does your meter have low light and daylight settings (like the leica meters) ?

    You have to eliminate one variable at a time.
    The Kodak is just the usual two stages with a bellows, no gels etc, nowt on the lens eitherClick image for larger version. 

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    This is it picked up and brought inside, haven't moved bellows etc.

    Yes maybe the MF is off too, they are all the same vintage, but both MF shutters would have aged identically. But the MF and LF would still be eight stops different relative to each other. The MF works fine when set to the readings of the Weston light meter, whereas the LF MASSIVELY under exposes.

    Yes the Weston has a bright/dark flip up screen, but imho the light meter and Mamiya aren't at fault I've used them fine for two decades....

    It's just this darn new fangled large format!

  6. #26

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by Dan Fromm View Post
    Arrgh!

    Ross didn't make a "Telemetric." They made a telephoto lens called Telecentric.

    300/6.8 = 44, not the 25 you measured.

    You have a telephoto lens. The rear nodal point, from which extension is measured, is far in front of the diaphragm.

    You have a telephoto lens. It has considerable pupillary magnification. The f/ number is calculated as focal length/diameter of the entrance pupil. Measure the entrance pupil, not the diaphragm.

    There are books on LF photography. The two most commonly recommended here are Leslie Stroebel's View Camera Technique and Steve Simmons' Using the View Camera. Both available used at low prices from on-line booksellers, e.g., abebooks.com, alibris.com, amazon.com, bn.com, ... Buy one and study it. You'll learn more that way than from short random answers to random questions.
    Ok, entrance pupil is 50mm. I will look up "pupillary magnification" sounds painful.

    So, 300/50 is 6, seeing as its all actually in imperial that would work out about right for f6.8.

    I have lots of books and an internet, but it's much more companiable chatting to you guys. Try and find 'real' folk ready to talk about this stuff!!! Even 'photographers' just glaze over. My son just said "just take the picture with your iPhone!" Philistine.

    Anyhow, it's not doing what it's supposed to! Where's my light gone!?

  7. #27

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    Re: Help a noob understand the exposure conundrum

    Wiki says
    "The pupil magnification of an optical system is the ratio of the diameter of the exit pupil to the diameter of the entrance pupil. The pupil magnification is used in calculations of the effective f-number, which affects a number of important elements related to optics, such as exposure, diffraction, and depth of field. For all symmetric lenses, and for many conventional photographic lenses, the pupils appear the same size and so the pupil magnification is approximately 1."

    Which for my lens is 50mm entrance 25mm exit. Does this effect what light hits the ground glass relative to the aperture setting then?

  8. #28

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by TimberwolfII View Post
    Which for my lens is 50mm entrance 25mm exit. Does this effect what light hits the ground glass relative to the aperture setting then?
    No. The f/ number is all you need to know. Buy a book. Read a book.

  9. #29

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by TimberwolfII View Post

    I have lots of books and an internet.

    it's not doing what it's supposed to! Where's my light gone!?
    Books don't tell you how to trouble shoot, they tell you theory and protocol, what happens when theory and protocol don't work?

  10. #30

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    Re: Help a noob understand the exposure conundrum

    I checked and an Ilex 3 has a max iris of 34.6mm. A Copal 2, for example, has a max iris of 30mm, and a Copal 3 has a max iris of 45mm. Still, eight stops light loss is a lot.

    Maybe the OP could measure the diameter of the rear element of his lens.

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