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Thread: How To Properly Determine Infinity For a Lens?

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  1. #1

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    How To Properly Determine Infinity For a Lens?

    I want to make sure I fully understand how to determine infinity for all of my various large format lenses.

    I assume that I will need to know the flange focal distance for the lens and then from there, I really don't know how to use that information to determine infinity for each lens. I have both standard and telephoto lenses, so I am hopeful that someone here will teach me how to do this properly.

    Thanks in advance for teaching an old guy something new today.

    Larry

  2. #2

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    Re: How To Properly Determine Infinity For a Lens?


  3. #3

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    Re: How To Properly Determine Infinity For a Lens?

    You have properly cut cams, the infinity stops and focusing scales for your Technika?

  4. #4

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    Re: How To Properly Determine Infinity For a Lens?

    Hi Bob. Yes, I have a properly cut cam for my lens.

    I know the default answer is to send the camera to an authorized service center for setup and calibration, but I simply don't have months to wait, so I want to at least try and understand what is involved so I can make an educated attempt at trying to setup my lens on my Master Technika.

    I believe the first step is to set the lens at infinity and that is what I am asking the original question, but I want to make sure I know what that means so I start off with the lens in the right place on the rails.

    Any pointers are much appreciated.


    Quote Originally Posted by Bob Salomon View Post
    You have properly cut cams, the infinity stops and focusing scales for your Technika?

  5. #5

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    Re: How To Properly Determine Infinity For a Lens?

    Quote Originally Posted by LFLarry View Post
    Hi Bob. Yes, I have a properly cut cam for my lens.

    I know the default answer is to send the camera to an authorized service center for setup and calibration, but I simply don't have months to wait, so I want to at least try and understand what is involved so I can make an educated attempt at trying to setup my lens on my Master Technika.

    I believe the first step is to set the lens at infinity and that is what I am asking the original question, but I want to make sure I know what that means so I start off with the lens in the right place on the rails.

    Any pointers are much appreciated.
    Presuming your cam has the same serial number as your lens you install the cam. Focus on something several hundred yards from you. Marflex used a telephone pole and wires across the street from our offices. Focus through the gg till the wires and pole are as sharp as possible. Then look through the rangefinder to see if it agrees with the gg.
    If yes, carefully install the infinity stops against the front standard, carefully because the screws that fasten the stops have sharp pointed screws that will dig into the chrome plated focus tracks. If the stops are moved those screws will leave small pit marks in the tracks that can not be removed.
    If no your cam is not cut for your lens.
    When one buys a new cammed lens from the factory or the distributor the lens box comes with the stops and the focusing scale for the bed. Along with these you also get a cardboard tube that contains a focusing target and instructions. These items let you properly install the infinity stops at the proper position on the tracks when viewed from about 5 meters on the gg.

    It isn’t quite as simple as it would appear at first glance.

    Why would it take months to properly adjust your camera?

  6. #6

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    Re: How To Properly Determine Infinity For a Lens?

    Hi Bob, I was able to get the cam and lens all setup and everything works perfectly. I even exposed a couple sheets of film to confirm. I am super happy about this!

    In regard to the couple of months comment, that is the time it would take to ship the camera, wait for it to be serviced and then return shipped. Now I don't have to wait for any of this!!

    Thanks again.




    Quote Originally Posted by Bob Salomon View Post
    Presuming your cam has the same serial number as your lens you install the cam. Focus on something several hundred yards from you. Marflex used a telephone pole and wires across the street from our offices. Focus through the gg till the wires and pole are as sharp as possible. Then look through the rangefinder to see if it agrees with the gg.
    If yes, carefully install the infinity stops against the front standard, carefully because the screws that fasten the stops have sharp pointed screws that will dig into the chrome plated focus tracks. If the stops are moved those screws will leave small pit marks in the tracks that can not be removed.
    If no your cam is not cut for your lens.
    When one buys a new cammed lens from the factory or the distributor the lens box comes with the stops and the focusing scale for the bed. Along with these you also get a cardboard tube that contains a focusing target and instructions. These items let you properly install the infinity stops at the proper position on the tracks when viewed from about 5 meters on the gg.

    It isn’t quite as simple as it would appear at first glance.

    Why would it take months to properly adjust your camera?

  7. #7

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    Re: How To Properly Determine Infinity For a Lens?

    Quote Originally Posted by LFLarry View Post
    Hi Bob. Yes, I have a properly cut cam for my lens.

    I know the default answer is to send the camera to an authorized service center for setup and calibration, but I simply don't have months to wait, so I want to at least try and understand what is involved so I can make an educated attempt at trying to setup my lens on my Master Technika.

    I believe the first step is to set the lens at infinity and that is what I am asking the original question, but I want to make sure I know what that means so I start off with the lens in the right place on the rails.

    Any pointers are much appreciated.

    You can buy new cams and sharpen them yourself. I would prefer this solution. You don't have to "adjust" anything. You build yourself the cams you need, depending on the things you focus. You only need a file and a vice.

    Tschau zäme
    Last edited by Daniel Casper Lohenstein; 25-Aug-2020 at 03:05.

  8. #8

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    Re: How To Properly Determine Infinity For a Lens?

    Any tips or insights into how to go about doing this?

    Quote Originally Posted by Daniel Casper Lohenstein View Post
    You can buy new cams and sharpen them yourself. I would prefer this solution. You don't have to "adjust" anything. You build yourself the cams you need, depending on the things you focus. You only need a file and a vice.

    Tschau zäme

  9. #9

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    Re: How To Properly Determine Infinity For a Lens?

    Quote Originally Posted by LFLarry View Post
    Hi Bob, it works perfectly at all distances. I shot 3 sheets of film to confirm. 1 at infinity, 1 at about 100 ft. and 1 at about 25 ft. All three were tack sharp on the film as they were on the ground glass and in the rangefinder.
    Quote Originally Posted by LFLarry View Post
    Any tips or insights into how to go about doing this?
    Well, if your cams are tack sharp, everything is fine.

    Otherwise, I imagine that you mount a new cam, focus on the ground glass at a certain distance, 1m, with an aperture of 5.6, and then check whether the range finder is also sharp. If not, move the cam to see if something is missing (bad luck) or if there is too much on it. If there is too much, file it off carefully, but only at the region where the focusing slider bottom bolt touches the cam.

    This again is done successively for all distances, I think. I suggest not to finish the near point right away, but to file the near and far point and the middle evenly. This way you should slowly approach a sharpness in all areas. It surely takes time and requires intuition. Maybe that's why this is something that is done in the factory, by trained specialists. You don't tune pianos yourself, do you?

    Infinity at 5.6 and 150mm is assumed at about 24m, because of the hyperfocal distance at about 47m, given 0.086mm as circle of confusion at 30cm print width and 35cm viewing distance. 100cm print width at 35cm viewing distance gives 0.026mm as circle of confusion. Then everything will be sharp at 5,6 at 78m, with a hyperfocal distance of 156m. Cf.http://www.erik-krause.de/schaerfe.htm#top Correct me if I get it wrong

  10. #10

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    Re: How To Properly Determine Infinity For a Lens?

    Quote Originally Posted by Daniel Casper Lohenstein View Post
    Infinity at 5.6 and 150mm is assumed at about 24m, because of the hyperfocal distance at about 47m, given 0.086mm as circle of confusion at 30cm print width and 35cm viewing distance. 100cm print width at 35cm viewing distance gives 0.026mm as circle of confusion. Then everything will be sharp at 5,6 at 78m, with a hyperfocal distance of 156m. Cf.http://www.erik-krause.de/schaerfe.htm#top Correct me if I get it wrong
    This is the second time you've said something like "Infinity at 5.6 and 150mm is assumed at about 24m, because of the hyperfocal distance at about 47m," and I think that's misleading. 24m would be the near limit of acceptable focus when focused at the hyperfocal distance, not when focused at true infinity.

    Infinity is still at true infinity. Infinity (or really, something far away, like 100+ meters) is used to calibrate focusing systems because there's no question about where it is, and because it's one limit of the travel of the focusing system. Also, it often appears in photographs as the background. If you only use a rangefinder at 2-10 meters then you should certainly calibrate the rangefinder there, but I think it will generally be easier to calibrate a rangefinder by getting it correct at infinity first.

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