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Thread: Help a noob understand the exposure conundrum

  1. #1

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    Help a noob understand the exposure conundrum

    Hi everyone, first post!

    Been a lurker and generally familiar, although far from competent with 6x6. I love analogue, so have ventured into LF.

    I have a 'no budget' set up, scratched together off eBay and diy:
    Kodak specialist 3 rail camera
    Ross of London telemetric 6.8 300mm
    Elgeet no.3 universal shutter
    DIY brass lens to shutter converter
    Weston exposure meter.
    Home made film holder (camera is a half plate)

    Conundrum is: Weston is "accurate" for my Mamiya 330, ie if I do what it tells me I get decent negs.

    When I meter for the big Kodak I have to allow 8 stops more exposure (!) to get a decent neg.

    Why?

    Cheers, Rob

  2. #2
    8x10, 5x7, 4x5, et al Leigh's Avatar
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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by TimberwolfII View Post
    Conundrum is: Weston is "accurate" for my Mamiya 330, ie if I do what it tells me I get decent negs.
    When I meter for the big Kodak I have to allow 8 stops more exposure (!) to get a decent neg.
    Why?
    Hi Rob, and Welcome Aboard.

    That is a really odd situation.

    Commonly, old shutters slow down, so you need to use a setting for a faster speed than you really want.
    If you expose at the nominal marked shutter speed, negs will be OVER-exposed.

    I can't envision a shutter problem that would cause under-exposure.

    - Leigh
    If you believe you can, or you believe you can't... you're right.

  3. #3
    Nodda Duma's Avatar
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    Re: Help a noob understand the exposure conundrum

    Start with the basics:

    In sunny conditions, set lens shutter at f/16 and expose the film at 1/ISO. So if the film is ISO 100, expose for 1/100s. This should tell you if the shutter is operating properly at that setting.

    Reduce the aperture and correspondingly increase the shutter speed.


    Alternatively, down load the iphone app shutter speed and test your shutter that way.

  4. #4
    Vaughn's Avatar
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    Re: Help a noob understand the exposure conundrum

    Eight stops is too much for a simple problem!

    What film?

    Close-up photography? If so, exposure needed to be added to compensate for long bellows extension.

    Is you lens marked with modern f/stop system?

    Try an exposure that you time with a lens cap rather than the shutter -- a second long exposure or more. That will eliminate shutter problems.

    Test your shutter by firing a known good one at the same time -- at times around 1/4 sec or slower.
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

  5. #5
    Foamer
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    Re: Help a noob understand the exposure conundrum

    Eight stops--do you know if your shutter is the more modern system of f-stops (i.e. the British,) or the old U.S. (Uniform System) from around 1900? On both systems, f16 is the same. On the U.S. system, I think f8 is actually f11 in modern system. As for your question, the film is the same speed so exposure should be the same. Oh, the Mamiya will definitely have the modern f-stop system. There might be several exposure scales on your meter too--a bit confusing.


    Kent in SD
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  6. #6

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    Re: Help a noob understand the exposure conundrum

    Quote Originally Posted by Vaughn View Post
    Eight stops is too much for a simple problem!

    What film?

    Close-up photography? If so, exposure needed to be added to compensate for long bellows extension.

    Is you lens marked with modern f/stop system?
    Started with a portrait, subject got bored, ended with a tree! At about 2m distance both. Same light etc.

    Ok, more info:
    HP5 rated at 200
    Light meter set at asa 200, gives an indication of no.11 off a grey card, which cos I want the lens wide open (6.8) equates to 1/250-1/500. Via lots of trial and error I get a decent neg off the camera set at 1 sec 6.8. (Eights stops more than indicated?) Lens is 1912 so f stops are a bit funky but all there. Shutter sounds like about a second, faster speed is under exposed 4 sec bulb exposure over.

    The lens is physically about the same as the Mamiya 250 mm I have, in my head I'm wondering if so much light goes in through the hole in the lens and illuminates a 6x6 then the intensity of similar light through a similar hole hitting a 5x7 INCH neg area will be so much less intense?

    I can maybe just shift all the numbers along and go from there, but that's not very scientific and I'm trying to understand what's happening.

    I got into LF to really dial down into the theory, analogue stops me at first hurdle!

  7. #7
    jp's Avatar
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    Re: Help a noob understand the exposure conundrum

    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?

    If the film stays the same, exposure for one camera and film size will be the same for another camera and film size. (assuming you doing normal photos not closeups)

  8. #8
    Vaughn's Avatar
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    Re: Help a noob understand the exposure conundrum

    No -- there is no fundamental difference in lenses/formats that should cause a one stop difference, let alone 8.

    You are losing light due to the extension of the bellows past the focal length of the lens. Set up the camera the same way, measure the bellows and run this equation and see what factor you would need to increase your exposure: http://www.cookseytalbottgallery.com...mpensation.php also:http://www.largeformatphotography.in...ws-factor.html

    Also you might want to measure your aperature and run the equation to make sure you lens in marked with the proper modern f/stop system.

    https://en.wikipedia.org/wiki/F-number
    "Landscapes exist in the material world yet soar in the realms of the spirit..." Tsung Ping, 5th Century China

  9. #9
    Mark Sawyer's Avatar
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    Re: Help a noob understand the exposure conundrum

    At 2 meters, the bellows extension wouldn't be much of a factor, and would be the same on the medium format C330 at the same distances. In daylight with HP5 at f/6.8, 1 second is way too much exposure. As you're new to LF processing, I'd suspect development first.
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  10. #10
    jp's Avatar
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    Re: Help a noob understand the exposure conundrum

    It could be the film is loaded facing the wrong way.

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