Box of lenses.

Discussion in 'Ultra Large Format Cameras and Accessories' started by MCrooks, Mar 20, 2016.

  1. MCrooks

    MCrooks Member

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    First a bit of background. I'm in the very early stages of building a 16x16 wet plate camera.

    So this weekend at a estate sale when I saw a box of lenses I couldn't resist. This is what I got.
    https://drive.google.com/file/d/0B0x4BFkDspnrLUhCbVNnWTdfaWM/view?usp=sharing

    I had the most hope for the Paris Darlot and a new process lens with markings of 150mm and f22 (on lensboards)
    There is also a Wallensak Velosticmat series II 12" lens but its ruff, has no iris and won't cover my area.

    With that in mind I whipped up this lens tester to see what I had. Its nothing fancy just a 16" square box with a piece of velum on one end and lens board on the other. it does the job but not well.
    https://drive.google.com/file/d/0B0x4BFkDspnrN3pPRHJxR01sSzg/view?usp=sharing

    After testing the first two lenses I found that the Paris Darlot came into focus at 16" from the subject and covered no problem. The process lens had great magnification but came into focused at 7.5" from the subject. Could be great for macro but not what I'm after. Am I doing something wrong? Can't seem to find focus on subjects further away then 16".

    So my question is, is there a better way to evaluate the lenses short of building a lens board for each and pushing and pulling my box halves together. Only the three lenses mentioned have any marking the rest are total unknowns. Some have glass elements on the front while others have it on the back of the barrel. I'm waiting on View Camera Techniques from the library when it is transferred in to freshen up on my operations but any help/advice in the mean time would be greatly appreciated.
     
  2. frank

    frank Member
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    Won't lenses focus at any distance if you move them closer/farther from the film plane?

    You've built a sliding box style camera. Slide the boxes closer together. You may have to make them shorter to do this.
     
  3. markbarendt

    markbarendt Member
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    Focus at infinity is as close to the film as the lens will ever focus, as the subjects get closer to the camera the lens has to move farther from the film.

    Roughly, if you move the lens you saw focus at 16" out to ~ 32" it will probably focus on a subject that is 32" from the lens. The subject should look the same size on film as in real life at that point.
     
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    MCrooks

    MCrooks Member

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    Thank you Frank & Mark! This is what my monkey brain was trying to come up with but simply couldn't. Googles no good when you can't think of the right terminology and you can't frind your notes from 15 years ago. So it sounds like I'll just have to make a lens board for each and play around.
     
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    MCrooks

    MCrooks Member

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    Ok I have now tried the doubling the bellows to 32" and moving the subject out to 32". No luck I had my girlfriend move it away and towards the lens and when it was 16" away it was tack sharp. I repeated with the box at 40" extension the only place I could find focus was with the subject ~16" from the lens. Any thoughts?
     
  6. frank

    frank Member
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    set up the camera so that the lens focuses on an object 16 inches away, now move the lens closer to the film plane. It should now focus on objects farther away.

    It is perhaps counter-intuitive: the lens focuses closer the farther it is from the film plane.
     
    Last edited: Mar 20, 2016
  7. wiltw

    wiltw Subscriber
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    I do not understand what you are trying to figure out about each lens!

    Any lens FL will focus to 1:1 reproduction scale (lifesize) when the subject is 4*FL from the focal plane.

    A 10m tall object which is 10m away will fill the short direction of a 93x120mm (4x5) image, with a 100mm lens which is about 100mm to the focal plane
    A 4m tall object which is 10m away will fill the short direction of a 93x120mm (4x5) image, with a 250mm lens which is about 250mm to the focal plane
    A 2m tall object which is 10m away will fill the short direction of a 93x120mm (4x5) image, with a 500mm lens whch is about 500mm to the focal plane

    But the distance to the focal plane can be farther if the object of interest is close to the lens...the distances to focal plane mentioned about assumes the object being focused is at Infinity distance from the lens!
     
  8. ic-racer

    ic-racer Member

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    If you are testing for coverage at infinity, your subject would be a distant horizon or other thing 1500x or so, farther than the estimated focal length.
     
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    MCrooks

    MCrooks Member

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    Thanks for the info Wiltw. The problem I'm working through is that 4 of the 6 lenses I picked up have zero markings and a single element so I'm trying to figure out focal lengths, coverage area and the like. I just finished making lens boards for the remaining four in the spare seconds around honey-dos. Also I just found the lens equation and the magnification equation so I can start working through some of the math. ic-racer Thanks for the info about focusing at infinity, I'll have to truck the setup out to plains once I figure out my focal length to test infinity because I sure don't have that much space here.
     
  10. wiltw

    wiltw Subscriber
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    For any non-retrofocus design or any non-telephoto design, the distance from the rear node of the lens to the focal plane, when the subject is at
    'infinity' distance is the FL, but then you need to guess where is the 'rear node' in the lens!
    If you put an ooject sufficiently close and focus for 1:1 magnification at the focal plane, the subject-to-focal plane is 4*FL and you need not guess the location of the rear node.

    As for what distance is sufficient for 'infinity', if we assume a 10" FL lens then 1500*FL is about 1/4 mile away.
     
  11. jnanian

    jnanian Advertiser Advertiser
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    hi mcrooks

    have a look at this thread, it makes things easy.
    (there was a url link here which no longer exists)
     
  12. Cary Lee

    Cary Lee Member

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    Look here

     
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