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Thread: Creating lens aperture scales - what a project!

  1. #21

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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Robert A. Zeichner View Post
    Measuring the comparative diameter of these two shutters is not as easy as you might think. The Compur shutter has many more blades in its diaphragm creating what appears to be almost a perfect circle. The Copal shutter's diaphragm contains fewer blades and the result is more of a polygon making measurement more of a challenge. By simply measuring the light passing through a known aperture, it was pretty easy to adjust the diaphragm on the Copal shutter to achieve the 1/3 stop increments.
    If you want to be picky measure it at the smallest value for both of them - the shape difference is negligible - the highest value are compensated by the lowest ones to result in the same average value. Still it'll be more precise than introducing all the errors you get with your exposure meter method. Also it is not difficult to measure the average value with a calliper if you want to open it in between the smallest and the highest value.

  2. #22

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    Re: Creating lens aperture scales - what a project!

    Y'know, if you want to use photometric methods the best meter to use is probably the Horseman TTL meter. With a 203 mm lens a 6x9 meter will give good measurements in a 4x5 camera. And with a coated lens that has eight surfaces the photometric t/stop will be within 0.1 stop of the geometric f/stop.

  3. #23

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    Re: Creating lens aperture scales - what a project!

    I did exactly that..in a dark room...camera pointed at light grey card that filled the view - then took relative reading from the back ofthe GG

    I used a minolta meter that had a flat (for enlarging?) disk in place of th dome though

    it seemed to work out okay

    my issue - what did you use to mark the tape with?? I think I used a micro point sharpie that eventually smeared and rubbed off

  4. #24
    IanG's Avatar
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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Robert A. Zeichner View Post
    Measuring the comparative diameter of these two shutters is not as easy as you might think. The Compur shutter has many more blades in its diaphragm creating what appears to be almost a perfect circle. The Copal shutter's diaphragm contains fewer blades and the result is more of a polygon making measurement more of a challenge. By simply measuring the light passing through a known aperture, it was pretty easy to adjust the diaphragm on the Copal shutter to achieve the 1/3 stop increments.
    Your f45 setting is over a stop out, it should be around half way beneath the 1/2 and 1/4 second markings. If you used a standrad 210mm scale then the f45 setting would actually be f43.5 with the 203 Ektar cells fitted., so the f45 setting would need to be a fraction closer to the 1/2 but it would be accurate enough as is. That's from the aperture scales of a 210 Symmar S and an f4.5 210mm Osaka Commercial, and all Copals have a similar equal scale spacing between each F stop unlike early Compurs Dial & Rim set.

    I really don't think your methodology with a light meter is working, particularly at lower light levels.

    Ian

  5. #25
    Robert A. Zeichner's Avatar
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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by DrTang View Post
    I did exactly that..in a dark room...camera pointed at light grey card that filled the view - then took relative reading from the back ofthe GG

    I used a minolta meter that had a flat (for enlarging?) disk in place of th dome though

    it seemed to work out okay

    my issue - what did you use to mark the tape with?? I think I used a micro point sharpie that eventually smeared and rubbed off
    I first marked the tape with a .3mm mechanical pencil and proceeded to go up and down the scale marking all the other aperture settings, using the meter and probe to confirm the incremental changes. I then removed the aperture scale and inked in the lines with a 00 reservoir pen from one of my many Leroy lettering sets. As long as I was at it, I figured I would letter in the apertures with a size 60 Leroy template. This was done with India ink.

  6. #26

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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by IanG View Post
    Your f45 setting is over a stop out, it should be around half way beneath the 1/2 and 1/4 second markings.

    I really don't think your methodology with a light meter is working, particularly at lower light levels.

    Ian
    Indeed, it could be easily measured if a linear movement of the aperture lever translates into linear changes of the actual aperture opening.
    Last edited by Pfsor; 13-Mar-2017 at 10:25.

  7. #27
    IanG's Avatar
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    Re: Creating lens aperture scales - what a project!

    Robert, apologies I confused your two scales the end and start points f7.7 and f45 do appear close to correct but that scale should be linear, all Copal shutters and the very late Synchro Compurs are.

    It's the key aperture f22 that appears to be maybe 2/3rd of a stop out.

    Ian

  8. #28

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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by IanG View Post
    Robert, apologies I confused your two scales the end and start points f7.7 and f45 do appear close to correct but that scale should be linear, all Copal shutters and the very late Synchro Compurs are.

    It's the key aperture f22 that appears to be maybe 2/3rd of a stop out.

    Ian
    Indeed, as many posters noted and I can confirm, Copal scales are linear - the simple fact that Robert's home-made Copal scale is not linear clearly indicates that he managed to introduce an error while creating his lens aperture scale.

  9. #29

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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by DrTang View Post

    I think I used a micro point sharpie that eventually smeared and rubbed off
    Use a layer or two of clear varnish to paint the scale with - I used this solution on my focusing scales and never needed to replace them.

  10. #30
    Les
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    Re: Creating lens aperture scales - what a project!

    Robert, correct me if I'm wrong, but couldn't you just block off the F5.6 and use <one notch before F8> (for your F7.7)....without having to alter the Copal 1 scale ? Thanks.

    Les

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