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Thread: Creating lens aperture scales - what a project!

  1. #11
    Robert A. Zeichner's Avatar
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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Dan Fromm View Post
    Hmm. Not to be a complete idiot, but was the Compur unfixable?
    Actually, there was nothing at all wrong with this shutter. I simply wanted to move the lens to a more modern
    Copal shutter like most of my other lenses.

  2. #12

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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Robert A. Zeichner View Post
    First of all, I removed the fresnel as this was simple in that it was mounted between the gg and my eyes. Since I was not taking any sort of an absolute measurement of light, but rather was using the meter simply to compare the amount of light passing through the lens set at known f22 aperture with that of a shutter for which I had no calibrated scale, I don't think the absorption of light by the gg was of any consequence. Once I was able to meter the light from the known aperture, all I had to do was to remount the lens in the unmarked shutter and move the aperture lever until the reading I got on the meter was the same. From there, it was only a matter of moving the lever an amount that would increase or decrease the meter reading by 1/3 stops and marking the scale accordingly.
    The Fresnel spreads the light evenly across the gg so it should not have been removed to take the readings.
    You can confirm how much light was lost by Metering a gray card and then comparing that reading to the one through the gg. There is a light loss.

  3. #13
    Robert A. Zeichner's Avatar
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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Bob Salomon View Post
    The Fresnel spreads the light evenly across the gg so it should not have been removed to take the readings.
    You can confirm how much light was lost by Metering a gray card and then comparing that reading to the one through the gg. There is a light loss.
    The diameter of the fiber optic probe is roughly 1/4". When holding it against the crosshairs of my gg, I seriously doubt my measurement would have been more accurate with the fresnel in place. Once again, I was not interested in "metering" the image at the gg for the purposes of making an exposure. Of course a gg and fresnel would attenuate the light as compared with what would strike the film and that is covered in the operation manual that came with the probe. All I was interested in was making a comparison between the aperture of one shutter with another. The small size of the probe made this easier as I could come closer to pinpointing the exact spot from which I made my measurements.

  4. #14
    hacker extraordinaire
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    Re: Creating lens aperture scales - what a project!

    The OP's method is completely valid and possibly the best available way to go about it, if a known trusted lens is available. All the objections in this thread are nonsense.
    Science is what we understand well enough to explain to a computer. Art is everything else we do.
    --A=B by Petkovšek et. al.

  5. #15
    ic-racer's Avatar
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    Re: Creating lens aperture scales - what a project!

    I have about ten lenses in Copal shutters and none of the aperture scales spreads out like that. But you got what you got.

  6. #16
    Jim Jones's Avatar
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    Re: Creating lens aperture scales - what a project!

    Neat job, Robert. I haven't used a Leroy lettering set for decades. Even an old fossil like myself would have made a chart of the diaphragm diameter as viewed through the front lens group for each desired f/number and made a temporary scale as you did, using this chart. For this, viewing the diaphragm diameter should be done from a considerable distance to eliminate parallax error, or the eye can be shifted by about the apparent diameter of the diaphragm. Scanning that scale lets one make a finished scale in Irfanview or almost any other image editor. That finished scale can be scaled up or down to fit any other lens mounted on that shutter.

  7. #17
    IanG's Avatar
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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by ic-racer View Post
    I have about ten lenses in Copal shutters and none of the aperture scales spreads out like that. But you got what you got.
    I think you're right, the spacing on all my Copal shutters is not like that it's equal spacing between every f-stop. I'd actually copy the f-stop scale from a 210mm Symmar/Sironar shutter, the difference between a 203mm and 210 mm lens for the same aperture is very small and insignificant, the OP could adjust for it in positioning anyway if needed.

    At the moment some stop markings are quite significantly out, I'd need to check my 210mm Symmar S, plus I have a spread sheet for calculating corrected apertures for the same Shutter with different FLs fitted.

    Ian

  8. #18

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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Robert A. Zeichner View Post


    I first needed to make some light measurements with the old shutter.
    The fiber optic probe appeared to work very well and the Gossen's scale was marked in 1/3 stop increments, so I was able to make some repeatable measurements. I decided to use f22 as my starting point as that would be the aperture I would most likely use with this lens most of the time. I set the Compur to f22 and took a measurement. I checked the other apertures and much to my satisfaction, the meter tracked them perfectly.

    I remounted the lens in the new Copal shutter and without changing the setting on my meter, I was able to find an aperture that gave me the same reading as f22 on the Compur shutter. I now have one of my favorite lenses mounted in a modern reliable shutter. Please forgive the iPhone photos.
    I don't understand why you went all this way of measuring with your exposure meter. After all - if the lens elements are the same in both shutters with identical spacing, all you need is just to have the same aperture opening in both shutters to get identical amount of light to go through. Why not just measure the actual aperture diameter and set it on the new shutter to the same value and mark the scale? If both the shutters have the same inner dimension then the same opening diameter must give the same result optically, regardless of the name on the shutter label!

  9. #19
    Robert A. Zeichner's Avatar
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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Pfsor View Post
    I don't understand why you went all this way of measuring with your exposure meter. After all - if the lens elements are the same in both shutters with identical spacing, all you need is just to have the same aperture opening in both shutters to get identical amount of light to go through. Why not just measure the actual aperture diameter and set it on the new shutter to the same value and mark the scale? If both the shutters have the same inner dimension then the same opening diameter must give the same result optically, regardless of the name on the shutter label!
    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.

  10. #20

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    Re: Creating lens aperture scales - what a project!

    Quote Originally Posted by Robert A. Zeichner View Post
    Gossen Luna-Pro
    You can take advantage of modern times.

    Have you an Smartphone ? Then you have a precision tool !!

    Just download a Luxometer App from google play. It uses the front photocell that is intended to measure ambient light for screen auto level.

    It is not a photographic tool in the sense that is directional (you should place a translucid dome on sensor and calibrate that in the app), but it will deliver very accurate relative readings, from some 30 to some 30000 lux in the case of my Xperia Z2. Use stored Max max reading, as you won't see screen while reading, as potocell is also in the front side.

    You also can buy a cheap handheld luxometer (some $20) This goes from 0.01 lux to 300.000 lux. Also useful to plot film calibration curves.

    Take the readings with no GG.


    Plan B:

    Just place a DSLR or SLR in the back of the view camera (without lens), you have to manufacture a simple attachment or use a second tripod for the SLR. I used my F5 for the same. You have to know the flange to sensor(or film) distance to give the right bellows extension.



    Regards.

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