Aperture scale on shutter Pi-ALPHAX

Discussion in 'Large Format Cameras and Accessories' started by originalphoto, Apr 18, 2011.

  1. originalphoto

    originalphoto Member

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    I have a Wollesak 61/4'' (159mm) f/12.5 lens with Pi-ALPHAX shutter. Aperture scale shows 16, 11, 8, 5.6, 4, 2.8, 1.9. My question is if this is an original shutter for this lens? if yes, how to convert this scale to current standard F-stop?
     

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  2. holmburgers

    holmburgers Member

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    Well, obviously it's not the original shutter, or at least not the right aperture scale.

    My first thought is, if you're on f/1.9, does that equate to this lens's f/12.5? If so, it would just be a matter of mathematics to figure out the conversion.

    If for some reason this shutter at 'wide-open' doesn't perfectly equal the largest lens diameter (perhaps the construction of the lens cells aren't identical to the previous lens), then you could focus on a grey card and meter the ground glass. Then it would just be a matter of marking the points on the scale where the light is 1 stop less. Make sure the grey card is far enough away to not introduce any bellows factor.

    I hope that makes sense; I'm sure others will chime in with better advice.
     
  3. k_jupiter

    k_jupiter Member

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    The scale was set up for a 90mm (I think) f 1.9 lens that was used as a o-scope camera. Useless as a LF lens as the infinity distance is somewhere round 8 inches. If I remember correctly, there are only three speeds on the shutter. That is not some weird scale, just a weird lens. Make a new scale by doing the math. I would suspect the intra-lens distance as this is not the original lens for the shutter and quite possibly was just put in there by a previous owner who found a shutter that the threads (hopefully) matched.

    Good luck.
    tim in san jose
     
  4. Ian C

    Ian C Member

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    The marked shutter speed sequence is the same as on my Rolleicord from 1 second to 1/50 second.

    The aperture value = f/D where f = focal length of the lens and D = the diameter of the aperture as measured at the front.

    For example, if you set the aperture lever so that the measured aperture diameter was 9.9mm, then the approximate aperture value is

    A = f/D = 159mm/9.9mm = 16.06 or approximately f/16.
     
  5. darinwc

    darinwc Subscriber

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    Out of curiosity, what is the thread size of the front and back cells?
    THX
     
  6. cyberjunkie

    cyberjunkie Member

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    Please, try to post about facts, not personal conjectures.
    The Wolly Ext WA Velostigmat (previously called Series IIIA) 159mm was sold in barrel, as well as in shutter. The latter were housed in Betax No.3, and later on, in Alphax No.3, IIRC. The Pi-Alphax used on monoscope cameras should be dimensionally identical to a No.3 used in conventional cameras.
    Sometimes everything won't work as expected: i have transferred a few lens cells from barrel to shutter with no problems, but once i found that an Alphax No.3, taken from a scope camera, gave nearly 1mm spacing error (that is, 1mm too much).
    Back to the specific question, it's very likely that the shutter wasn't choosen at random, just because the threads were more or less the same, but because it was a correct fit for the lens (which, BTW, is a desiderable one).
    If the lens takes sharp pictures, it's easy to use the existing diaphragm scale as a reference, or make a new one. There is a lot about that on the Web. I use a an old Sinarsix to double check a new scale, but it's not mandatory, of course! :smile:
    I encourage other users to share on this forum their successful experiments with lens cells/shutters surgery. Of course there are plenty of barrel lenses that don't fit in shutters (without expensive custom-made adapters), but some do., and there are very little infos available about that (excluding vintage Schneider glasses).

    Have fun

    CJ
     
  7. k_jupiter

    k_jupiter Member

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    That is rather rude.
    You used 'should' instead of 'is'. That is conjecture. 'Is' is definitive.
    Since you don't know jack about this conversion, you have no idea if the previous owner knew his butt from a hole in the ground. You theory that it was chosen for the spacing is conjecture.
    Then you point out that while those two shutters 'should' be identical,you have found ones that are not.
    So all I said was look at the spacing to make sure the cells are correctly distanced from one another.
    Thanks for your input.
    tim in san jose
     
  8. cyberjunkie

    cyberjunkie Member

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    Sorry, i didn't mean to be rude.
    I was trying to point out that, from my own experience, the vast majority of lenses housed in non-original shutters have spot-on spacing.
    Being more specific, the only time i had a problem it was a minor one: Computar Symmetrigon 150mm cells were fitted in a No.1 shutter with non-standard diaphragm opening (Copal/Polaroid press shutter from a gel cam, with smaller_than_average max aperture, correct cell_to_cell spacing, and the usual slightly recessed diaphragm plane). Probably a makeshift solution, from a present-day user, to be able to quickly sell the lens. All "vintage" adaptation works are very good, at least all those i have personally seen. Probably it was much easier to find a good mechanic, with lot of experience, and the asked prices were also more affordable. Even when high level workmanship was involved, as in re-coating, re-polishing or re-cementing old glasses.

    Back to the specific: all Betax No.3 shutters i have seen had the same spacing, and were a perfect fit for the corresponding barrel lenses. Unfortunately the Betax has a limited speed range and no flash sync. So an Alphax should be a better choice for most users. What's unfortunate is that there were many sub-variants, like the Pi-Alphax, used on scientific cameras. IIRC, i have even seen a few examples without the threading for retaining ring.
    So, you're right. The correct word is "should". Most of the times it should fit with correct spacing, but you can't be sure beforehand.
    My 159mm Wollensak, purchased in barrel (with a "project" Korona 8x10" still waiting for a couple of missing parts), was immediately fitted in a Betax No.3, keeping its correct spacing. I must admit that i choose the Betax for "historical" reasons, because the two were of the same vintage (the serial was from a time when the lens was originally sold in Betax). All the Alphax i used proved to be as satisfying, until i found an example that was a little too "fat". I had a 7" Radar Ext. WA waiting for a shutter, and that Alphax had a bi-post to pc-sync flash adapter, and was just CLA'ed. Sadly the correct spacing was not respected (about 0.8mm longer).
    A small side note: it's perfectly normal to find something like that with repro lenses. The different spacing between shutter and barrel versions are due to a different optimization. Barrel lenses are optimized for a reproduction ratio close to 1:1. If you transfer the same lens cells in a standard shutter, you'll get a better optimization for general photography.
     
  9. Jim Noel

    Jim Noel Member

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    I have dealt with these lenses several times over the years when I had a store. I also have two for personal use.
    I have seen many of these lenses remounted in Pi-Alphax shutters, some with new aperture scales and some without. So many have passed by me in these shutters I suspect one of two things has happened over the years.
    1. An unknown person or dealer did a lot of this particular re-mount
    and/or
    2. An article may have been written in one of the many good periodicals of the past suggesting this is a good re-mount.