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Thread: darlot lever stop hemispherical

  1. #11

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    Re: darlot lever stop hemispherical

    Most information known is already above. They didn't put a "No. 2" or a size on the lens, so to determine which you have (from the catalog above) you'll need to measure focal length. Good lenses.

  2. #12

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    Re: darlot lever stop hemispherical

    It will be interesting to play with once mounted for the camera. First thing I'll do is try to figure out the focal length and then apertures.

    Thanks!
    David Aimone Photography
    Critiques always welcome...

  3. #13

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    Re: darlot lever stop hemispherical

    This little lens arrived today, and I jury-rigged it onto my 4x5 just to take a look. It looks VERY promising from the ground glass. i can't wait to get it mounted on a board and use it.

    A couple of things though.

    First, I thought this would be much more of a wide angle than it is. But I guess being a 5 inch focal length it wouldn't be that wide.

    Any easy way to tell for sure what the aperture of this lens is wide open, and with each of the aperture levers operating?




    David Aimone Photography
    Critiques always welcome...

  4. #14

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    Re: darlot lever stop hemispherical

    one more:



    serial number 539
    David Aimone Photography
    Critiques always welcome...

  5. #15

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    Re: darlot lever stop hemispherical

    Enjoy the lens, they're nice. They are about a 90 degrees, and are about F15, if I recall. You can measure that by dividing the focal length by the apparent width of the light circle looking from the front. If you read this post, there is a reasonable explanation of what the lever numbers mean.

    Finally, the very early ones were a unique hemisperical design, later they changed to just a wide angle rectilinear...but kept the name. Check your serial number, I bet there is a digit you can't see under the hood, making it at least 4 digits, not 3.

    Here are my no. 3 and no. 4.

  6. #16
    Jon Wilson's Avatar
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    Re: darlot lever stop hemispherical

    These are nice lens. Here are are a couple of shots I took with my 6 inch WA Darlot at the local military cemetary last memorial day. One is a picture I took of David Bowie's and another solder's headstones and the other is another angle of the cemetary. These lens work well even with fuji provia. Jon
    Last edited by Jon Wilson; 2-Aug-2010 at 22:19. Reason: wrong picture posted

  7. #17
    neophyte
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    Re: darlot lever stop hemispherical

    Quote Originally Posted by iogdka View Post
    Any easy way to tell for sure what the aperture of this lens is wide open, and with each of the aperture levers operating?
    From the information provided by Eric #3 is 3x exposure ie 1.5 stops down; then #5 and #7 respectively 2.5 and 3.5 stops down.

    If this was f16 to start with (how to work out base f stop is found elsewhere in this forum. Briefly requires you to first to work out focal length and then find exit pupil size and then calculate f stop=aperture/focal length) you would have

    no stop: f16
    #3 ~f26
    #5 ~f38
    #7 ~f53
    If i understand correctly how the stops work, adding a #3 to a #7 just gives you a #7 and so on.

    Jon it is interesting to look at old photos and see how sharp the plate negative based ones are: these old lenses were good, but I did not expect very much in colour!
    "In the field of observation chance favours the prepared mind" -- Pasteur

  8. #18

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    Re: darlot lever stop hemispherical

    Thanks to everyone for the exhaustive information. It's clearer now. I just have to estimate the focal length and everything else should fall in place. Those apertures are small enough I may not even have to use a shutter all the time.

    David
    David Aimone Photography
    Critiques always welcome...

  9. #19

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    Re: darlot lever stop hemispherical

    Ok, to measure the focal length on this lens, do I measure from the plane of the shutter, the front of the lens or the back? From the shutter to the rear focal point at infinity is about 6" or about 150mm. From the rear of the lens it's about 5.5 inches or 140mm. From the front about 6.5 inches or 190mm. The front lens diameter (glass) is about 1.25 inches.

    My guestimate is that the shutter full open is about 12mm; with the 7 lever about 7mm; the 5 lever about 5mm; 3mm for lever 3, which makes sense with the numbers on the levers.

    So if I assume it's 6" (which doesn't fit the old brochure posted in this thread), the wide open aperture would be f/12.5; lever 7 at f/22; lever 5 at f/30 and lever 3 at f/50 (f/11.6, f/20, f/28 and f/47 at 5.5 inches).

    Am I even in the ballpark???
    David Aimone Photography
    Critiques always welcome...

  10. #20
    multiplex
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    Re: darlot lever stop hemispherical

    when i did the measurements and calculations for mine
    i came to the conclusion that the numbers on the levers
    were the aperture size in millimeters.
    it wasn't hard to convert the focal length to metric and divide.
    my apertures ended up something like 16-11-8-5.6(open) ...
    i am not a stickler for exact numbers so if they are a little off,
    i don't worry about ( i am currently shooting paper negs with the lens ) ...
    when i was using the lens on a 4x5 with film, i used the same
    computed fstops and they were fine as well ... so i couldn't have been too far off.

    have fun with your new lens !

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