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Thread: Fixed focus 4x5 camera

  1. #11

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    Re: Fixed focus 4x5 camera

    figure out what distance want to shoot from... build the camera to that.. then use a finder from a Polaroid 'Big Shot' to get you to that distance

  2. #12

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    Re: Fixed focus 4x5 camera

    I only have one big shot. So not gonna mess that one up. :-)
    Stupid questions deserve stupid answers.
    allthingsanalogue.weebly.com
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  3. #13

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    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Dan Fromm View Post
    The OP is going to have to get his lens, decide the distance at which his fixed focus camera should be focused, measure his lens' flange-focal distance when focused at that distance and then build his camera.
    That is a highly theoretical approach which shows you have not built a camera using this sequence, I'm afraid. The practical difficulties you find in doing so are rather great - the difficulty to exactly measure the lens FFD, (using gg focusing, just try it and you'll see how difficult it is to find the plane where you put your callipers) the difficulty to build a camera with this exact space between the gg and the lens flange (with many parts in between) and the difficulty to do so while maintaining the lens plane parallel to the gg plane (very important for a lens of such a short FL).
    A much better approach and much more practical is to built the lens into the camera in a way that it can be slightly moved forward and backward - even just 5mm is enough. In this way you can measure the lens FFD and built the camera with less precision and find the precise infinity focus while moving the lens to its right position. It is much easier this way.
    There is a way you can fine focus the lens (using 4 rods) and fasten it in the precise position and be done with it regardless of the precision of your measuring and manufacturing of the rest.
    Been there, done that. I have built fix focus cameras with lenses ranging from 90mm to the long telephoto of 800mm. Knowing what you want to use it for is necessary - my 800 mm camera is always used at objects in the realm of practical infinity. The 90, 135, 150, 180, 300mm lens cameras are also usable at shorter distances with no surprises at all.

  4. #14
    Jac@stafford.net's Avatar
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    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Pfsor View Post
    That is a highly theoretical approach which shows you have not built a camera using this sequence, I'm afraid.
    That is a risky assertion when it concerns Mr. Fromm's work.

    Building a box camera is simple enough if one has the fundamental measurements that Dan posted, AND a focus helical. Build the body as very close to the required metrics, which can be done with striking accuracy, and the focus helix can make up for the micro-millimeter difference.

    When I built my first, all I used were Mitutoyo gauges and decent, not outrageous wood machnes. Sure, actual focal lengths vary. I have years of experience with military lenses in which every single one was marked with absolute focal length, and then shimmed to accommodate the camera. (For land-based photography their metrics were overkill, overly expensive.)

    This one had the board very carefully micro-planed, then using a compliant (variable compression) gasket the back was settled into accurate infinity focus. Eighteen years later it is no longer in spec, but adjustments to the helix and retorquing the gasket makes new, accurate alignment trivial. Next week I am converting it from an early 47m Super-Angulon to a later 47mm XL thanks to help from one of our LF members.

  5. #15

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    Re: Fixed focus 4x5 camera

    Jac, the OP doesn't want to use helical, see the 1st thread. And believe me, I know what difficulties you would fall in if you just tried to put Dan's theory in practice. To "have the fundamental measurements" is not at all a given fact, see my reasoning.
    OTOH a helical focusing ring would be surely very helpful too, no contradiction in it.

  6. #16

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    Re: Fixed focus 4x5 camera

    a highly theoretical approach

    As the saying goes:

    "When Real World differs from Dan Fromm's theoretical approach, for sure, Real World is plain wrong."

    Not kidding (I stand corrected)
    - the knowledge of the focal length is useless, except if you want to re-compute your distance engravings on an helical;
    - the knowledge of the nominal flange focal distance of your lens is much more useful!
    - if you have a complete springback handy with a ground glass, this will definitely help;
    - adding 2 or 3 nominal numbers together to compute a measurement does not seem highly theoretical to me, but instead, as practical as can be in a mechanics workshop!
    - the depth of focus focus @f/16 with a sharpness criterion of 150 microns, is plus or minus 16x0.15 = plus or minus 2.4 mm; no need of a submicron caliper to properly set a working device, to re-use a well-know expression by physicist Charles H. Townes, one of the inventor of the laser: "Nothing stops naysayers like a working device" (C. Townes, 1999)

    Well, theoretical mechanics also exists

  7. #17
    Jac@stafford.net's Avatar
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    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Pfsor View Post
    Jac, the OP doesn't want to use helical, see the 1st thread. And believe me, I know what difficulties you would fall in if you just tried to put Dan's theory in practice. To "have the fundamental measurements" is not at all a given fact, see my reasoning.
    OTOH a helical focusing ring would be surely very helpful too, no contradiction in it.
    Okay, thank you for that. Now I see that I drifted to my own preference. I am sure if the OP builds a camera with enough of a 'ball park' measurement without a focus helical he will be happy. I may be too fussy and have gone overboard. Again!

    Perhaps he could search the Web for HOBO 8X10 CAMERA

    Emmanuel: "When Real World differs from Dan Fromm's theoretical approach, for sure, Real World is plain wrong."
    We have very good humor here. Thanks for grounding our dialog in good spirit.

  8. #18

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    Re: Fixed focus 4x5 camera

    Without a focusing helical, a good idea is while building is to build up the lensboard so that it is a little short of the "proper" focusing distance, but has allowance for different spacers to be added to shim in final focusing distances...

    You can also test a mild close-up lens if you want to find another mildly closer setting if you are somewhere where you would be closer to your subject...

    You can also check out PVC/ABS plumbing fittings to find something threaded where when screwed in, it would be your hyperfocal distance, but slightly unscrewed for closer focusing (like an interior or garden path, etc)...

    A wire sportsfinder is good, but I like these kind of cameras to have a GG so I can confirm the focus setting, compose when the edges are important, and have the option to use a rollfilm back...

    Good luck!!!

    Steve K

  9. #19
    Jac@stafford.net's Avatar
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    Re: Fixed focus 4x5 camera

    Steve, finding shims has always been a problem for me.
    Wire sports finders work! Good of you to mention!

    I have poor eyesight which can no longer be corrected so I use viewfinders, and yes, wire finders. I wish to promote the idea.

  10. #20

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    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Emmanuel BIGLER View Post
    a highly theoretical approach

    As the saying goes:

    "When Real World differs from Dan Fromm's theoretical approach, for sure, Real World is plain wrong."

    Not kidding (I stand corrected)
    - the knowledge of the focal length is useless, except if you want to re-compute your distance engravings on an helical;
    - the knowledge of the nominal flange focal distance of your lens is much more useful!
    - if you have a complete springback handy with a ground glass, this will definitely help;
    - adding 2 or 3 nominal numbers together to compute a measurement does not seem highly theoretical to me, but instead, as practical as can be in a mechanics workshop!
    - the depth of focus focus @f/16 with a sharpness criterion of 150 microns, is plus or minus 16x0.15 = plus or minus 2.4 mm; no need of a submicron caliper to properly set a working device, to re-use a well-know expression by physicist Charles H. Townes, one of the inventor of the laser: "Nothing stops naysayers like a working device" (C. Townes, 1999)

    Well, theoretical mechanics also exists
    No, adding 2 or 3 measurements is not difficult, indeed. To take the 2 or 3 measurements is much more difficult, because of the practical difficulties you encounter. Where do you take the measure of the distance between the gg and the lens flange? Where do you put the callipers when the gg is inside the camera box and you calliper is outside of it? While measuring on the outside frame of the gg do you take into account the manufacturing imprecision you find on it? Before you add the 2 or 3 measurements you must find how precise you are when fiddling with your callipers on different parts of your "complete springback". Because the complete springback is not built to 0.01mm tolerance all over, you will soon discover.
    And then - if you think your gg plane can go off one side with 2.4mm and be happy then build such a camera for 65mm lens and be happy... When you focus your 65mm lens, moving the gg 2.4mm gives you the same focus, under your focusing loupe, doesn't it? It's just adding 2 or 3 measurements together, isn't it? After all, a camera is just a light tight box between a lens and gg, isn't it?
    I think, Dan is intelligent enough to know the difference between saying a theory and following it in the practical way.

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