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Thread: Fixed focus 4x5 camera

  1. #31

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    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Emmanuel BIGLER View Post
    Hello from France!


    Now in order to properly set your lens mount in front of your film holder, you have to take into account the film holder's depth, which is for modern film holders compliant with the ANSI standard
    - 2" x 3" and 4" x 5" : 5.0 mm +- 180 microns (0.197" +-0.007")
    - 5" x 7" : 5.8 +- 250 microns (0.228" + - 0.010")
    - 8" x 10" : 6.6 mm +- 400 microns (0.260" + - 0.016")
    Quote Originally Posted by Emmanuel BIGLER View Post
    - 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
    Interesting. I wonder why the OP needs to know the +- 180 microns tolerance on his film holder when the depth of focus for the film is plus or minus 2.4mm...

  2. #32

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    Re: Fixed focus 4x5 camera

    I wonder why the OP needs to know the +- 180 microns tolerance on his film holder when the depth of focus for the film is plus or minus 2.4mm...

    Good question for which I have no clue!

    The +- 180 microns tolerance = +- 0.007" (for 2x3, 3x4 and 4x5 holders) is reported here in this well-known document
    http://home.earthlink.net/~eahoo/page8/filmhold.html
    and data are supposed to come from an ANSI standard PIMA IT3.108:1998 that I have never read, like all other DIN or ISO standards actually, taking into account the high price you have to pay to get a copy of them

    And since I never read the ANSI standard for film holders, consequently I have absolutely no idea about the rationale behind depth tolerances in this standard!
    Those tolerances do not seem to be correlated with the classical theoretical depth of focus model = plus or minus N c, where "N" is the f-number and "c" the diameter of circle of confusion chosen as a sharpness criterion. Plus or minus 180 microns @f/16 would correspond to an improbable sharpness criterion c=11 microns, i.e. smaller than a diffraction spot @f/16 ...

    BTW there is an old discussion here in the archives related to tolerances on sizes for film holders: our readers like to be 100% sure of what they are using! (at least this was the case as of year 2001)
    http://www.largeformatphotography.in...older-Accuracy

  3. #33

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    Re: Fixed focus 4x5 camera

    Wow what a nice discussion. I will read everything later on and I do enjoy the enthusiasm from everybody. My plans are rather simple and consisting of the lens and lensboard it is on attached to a wooden box. On the other side or opposite side the filmholder at roughly the focal distance of the lens. Hoping the DoF of the lens will make up for a slightly out of ideal focus of the whole system :-)
    If the results suck I can always rebuild :-D

    The lens is on a Sinar lensboard. I do not want to use a groundglas. I plan on focusing with a piece of see thru paper and then fix everything. I then can see if I want the focus fixed on hyperfocal or normal infinity at a certain aperture that I think I will use most or is most convenient in most situations. A small list of DoF on various apertures should give me some guidance in what situation my image will be sharp using a certain aperture. Now I have to start building I am afraid :-) :-D
    Stupid questions deserve stupid answers.
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  4. #34
    Drew Bedo's Avatar
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    Re: Fixed focus 4x5 camera

    Degroto: I say go for it!

    Plerase report back as your project comes together and post pictures.
    Drew Bedo
    http://www.artsyhome.com/author/drew-bedo




    There are only three types of mounting flanges; too big, too small and wrong thread!

  5. #35

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    Re: Fixed focus 4x5 camera

    A small list of DoF on various apertures should give me some guidance in what situation my image will be sharp using a certain aperture.

    Simply provide us with a list of
    - preferred focal lengths,
    - preferred working f/#,
    - and preferred film formats,
    and downloadable free (although theoretical) DoF charts will appear here "magically"

  6. #36
    Jac@stafford.net's Avatar
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    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Emmanuel BIGLER View Post
    [...] I have absolutely no idea about the rationale behind depth tolerances in this standard! Those tolerances do not seem to be correlated with the classical theoretical depth of focus model [...]
    Might the standards be guided by manufacturing precision requisites rather than optical necessity?

  7. #37

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    Re: Fixed focus 4x5 camera

    Might the standards be guided by manufacturing precision requisites rather than optical necessity?

    Certainly.
    With tolerances for film depth taken as a certain proportion of actual depth value? Still difficult to understand the choice of the proper figures. I can understand, however, that bigger film holders need to be thicker in order to stay as rigid as possible when size increases.

    BTW I have found that the ANSI standard for film holders, together with many standards related to photography, film and slide projection, has been withdrawn in 2003!
    I do not know the exact meaning of "withdrawn" for a standard, but the text is still not freely accessible!

  8. #38

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    Re: Fixed focus 4x5 camera

    I will of course. My very crude first attempt to figure out how to measure the actual distance the lensboard has to be from the film plane is encouraging. But it is to dark now to focus on infinity. I'll keep you posted.
    Stupid questions deserve stupid answers.
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  9. #39
    Jac@stafford.net's Avatar
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    Re: Fixed focus 4x5 camera

    The suggestions to make some sort of pliable/compliant gasket under the lens board or on the back was excellent IF your camera is already dimensioned very close to one specific focal point, which is rather constricting and in this case unrealistic.

    An alternative is to use 1/16" (1.6mm) plywood in as many layers as necessary under the lens board as shims. That is what I am using to make my new 4x5 camera correct at infinity. You can, of course, make the focal point any distance you choose. If you use little wing nuts you can carry several shims of different thicknesses to choose different points of focus in the field. A pocket on the side of the camera to hold the shims would be cool. (Don't carry them a back pocket. They might bend)

    Measuring the flange focal distance is as simple as Dan Fromm mentioned. Just first insert a film holder with the film side slide removed. A finely marked steel ruler can help. And recall my earlier suggestion - you are going to use film holders, I presume. To visually identify focus you can put a 4x5" holder in the camera, then remove both the dark slides, and drill a 1/16" hole through the center of the back and through the film holder in one drilling. Finally, remove the film holder. Drill another hole in the back to fit your loupe. If you use a proper, affordable hole saw, the 1/16" hole already drilled will guide the saw to be concentric.

    No ground glass necessary. Then we should describe aerial focusing. Quite easy.

    Best of luck!
    Last edited by Jac@stafford.net; 16-Aug-2017 at 15:45.

  10. #40

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    Re: Fixed focus 4x5 camera

    Quote Originally Posted by Dan Fromm View Post
    Funny that you should ask. What I've done has been to mount the lens in question on a Speed Graphic board, put it on (surprise!) a Speed Graphic, focus to the desired distance, take the lens off, a drilled board with no lens on the camera and measure the flange-to-film distance with a depth gauge. The OP may have to borrow a camera to do this. Speed Graphic not necessary, it was what I had at the time.

    Its better than guessing, which is what using published flange-focal distances amounts to. Published flange-focal distances are great for finding out what can probably be done but that's not what the OP needs.

    About the need for focusing. The shortest lens I've had -- still have it -- for 35 mm is a 24 mm. It has to be focused for best results. My 35 Apo-Grandagon has to be focused for best results.
    I'll back up this suggestion from Dan, but I'll add something about the depth gauge...

    If your lensboard mounting hole is more than 1" dia, a good, cheap tool to measure would be an adjustable square from a hardware store... With a another test camera, focus the lens to subject at your desired distance, then remove lens (but not lensboard)... Then the ruler part is inserted through the lens hole (if it fits), have a film holder with a piece of scrap film loaded (with the dark slide removed), touch the end of the rule to the film,and slide the square until it touches flush with the area where the lens sits... Lock the rule to the square, remove, and read the distance... When setting up your new camera, Build/use the same distance you measured... Leaving it a little short of this distance and by leaving some room to adjust this distance will allow you to fine tune your final adjustment...

    Don't feel that you have to use the lensboard you have already, as you can easily make a new, smaller board that will match up to your design better, and might make it easier to build in some adjustments to fine tune your fixed focus,or maybe add some simple focusing device you can rig up...

    I might have missed it, but what lens FL/make were you thinking of using???

    Have Fun!!!

    Steve K

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