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Thread: Lens element sources and specs?

  1. #11
    Nodda Duma's Avatar
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    Re: Lens element sources and specs?

    Lanthanum glass is used quite often.. the radioactivity is so low that it is below natural background levels and thus not considered hazardous. I’d be willing to bet there is a lanthanum glasstype in more than 75% of modern high-performing visible optics. Thorium is very, very rarely used, and never used for consumer products.

    From my perspective, a modern Petzval is trivial to design and resultant images would be impossible to distinguish from those of originals. Technically easy. The problem is not enough demand for a reasonable price tag. Get a million fellow photogs buying them and it’s a different story.
    Newly made large format dry plates available! Look:
    https://www.pictoriographica.com

  2. #12
    Drew Wiley
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    Re: Lens element sources and specs?

    For the right price you can get almost anything optical made, and on schedule. Just make sure you already have the design specifics, and bring along your NASA, NSA, DEA, or other national government credit card without a credit limit on it. Private citizens are welcomed too, if you happen to be Elon Musk or Jeff Bezos, that is.

  3. #13
    Nodda Duma's Avatar
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    Re: Lens element sources and specs?

    Haha. I’ve been known to tell Program managers “we can do anything you want, as long as you throw enough money at it.” The look I get back hasn’t changed in 20 years.

    Quote Originally Posted by Drew Wiley View Post
    For the right price you can get almost anything optical made, and on schedule. Just make sure you already have the design specifics, and bring along your NASA, NSA, DEA, or other national government credit card without a credit limit on it. Private citizens are welcomed too, if you happen to be Elon Musk or Jeff Bezos, that is.
    Newly made large format dry plates available! Look:
    https://www.pictoriographica.com

  4. #14

    Re: Lens element sources and specs?

    There is a service in the Ukraine that resurfaces and recoats lenses. Search "Lens recoating" on E-bay or kievcameraorg.

    I've reground and polished photographic lenses to remove deep scratches (having made telescope mirrors, it isn't too hard). It does take considerable skill and custom made tools to fully maintain the curvature and precision of the surface being repolished. On a one-off basis, depending upon the lens and the amount of surface damage, it can take from several hours to a couple of person days to do this well. Multiply 8 hours by the hourly rate for a skilled technician and you can get an idea of what this is likely to cost, assuming you can find someone to do it. (BTW - I don't provide this service.)

    Presumably the Ukrainian firm is set up to do this efficiently and thus can charge a lower price.

  5. #15
    (Shrek)
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    Re: Lens element sources and specs?

    The more valuable and desirable lenses are not the Petzvals from the mid-1800s, unless it's for historical reasons, it's the experiments. The Koritskas, the Spencer Port-Lands, the Plasticcas, and other lenses that are intentionally not perfect. Seems to me a hobbyist has ample materials available, especially given the price of 3d printers to make the hardware and off-the-shelf single lens elements from supply houses, if one wanted to create new less-than-perfect optical systems.

    One would need an optical design software that will do simple systems for free (check?), an understanding of basic lens design, an understanding of why some lenses work as soft-focus and others are just bad lenses, and the willingness to experiment. It wouldn't cost tens of thousands of dollars to give it a whirl. We have a member who recently did exactly this, and produced a valuable new soft focus lens, as mentioned in this very thread. If you need it to look like a 19th century Petzval, just collect some brass projection lenses and replace the innards.

  6. #16

    Re: Lens element sources and specs?

    Hit and miss lens design was common in the 19th century and early 20th century. Mathematically based design is of course better - but there was a time before the math was well worked out and before it was a practical possibility to do much ray tracing. A lot of early lens design was by practical technicians who had only a crude understanding of the math. It is fun to try experimental lens construction and it can result in some interesting lenses. Once when I had little money but a box of surplus lens elements and and optical bench to run tests, I concocted a simple but excellent telescope eyepiece that I still use occasionally today. At the time I knew something about eyepiece design theory and what combinations to try, and that gave me a good starting point. I've also made some large diameter lenses with focal lengths in the range of 6 feet from stock components for a friend's camera obscura. The two element lenses arranged symmetrically on either side of a diaphragm worked quite well. Don't be afraid to experiment and see what works.
    Bill

  7. #17

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    Re: Lens element sources and specs?

    I came across this thread and thought one of my own might be of interest to you- a bit more achievable than doing scratch built stuff!

    https://www.dpreview.com/forums/thread/4605882

    "+10 to 4 'achromatic' close up diopter from telephoto zoom, in typical filter thread"

    Basically, off the shelf achromatic (or better), multicoated positive-power 'groups' from telephoto zooms for 35mm cameras. Glass diameters 45-60mm+, focal lengths 80-220mm+. Sometimes just a thick doublet, sometimes a doublet surrounded by elements, sometimes a doublet with a singlet infront of it (slight meniscus, plano convex).

    The focal lengths of these elements I described might make them abit better for medium format, but that's because I don't have many to hand- another source is those 300mm f6.3, 500mm f8 "wundertute" refractors..

    So, you could atleast make an achromatic 'landscape' lens, or some simple "symmetrical achromats".

    I would absolutely not go as far to say as you're making an equivalent to a computed Rapid Rectilinear, because quite literally saying they're both made of symmetrical achromats is saying... nothing, really- they're completely different in design.

    But don't be discouraged, much fun to be had. I'm sure weaker elements can be found.
    Bundles of vintage zooms can be had very affordably, you may need some tools to get the elements out (rubber bung, JIS screws, small flatheads) but worth your time in the long run. Easier when it's "one way"...

  8. #18

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    Re: Lens element sources and specs?

    Quote Originally Posted by eggplant View Post
    I came across this thread and thought one of my own might be of interest to you- a bit more achievable than doing scratch built stuff!

    https://www.dpreview.com/forums/thread/4605882

    "+10 to 4 'achromatic' close up diopter from telephoto zoom, in typical filter thread"

    Basically, off the shelf achromatic (or better), multicoated positive-power 'groups' from telephoto zooms for 35mm cameras. Glass diameters 45-60mm+, focal lengths 80-220mm+. Sometimes just a thick doublet, sometimes a doublet surrounded by elements, sometimes a doublet with a singlet infront of it (slight meniscus, plano convex).

    The focal lengths of these elements I described might make them abit better for medium format, but that's because I don't have many to hand- another source is those 300mm f6.3, 500mm f8 "wundertute" refractors..

    So, you could atleast make an achromatic 'landscape' lens, or some simple "symmetrical achromats".

    I would absolutely not go as far to say as you're making an equivalent to a computed Rapid Rectilinear, because quite literally saying they're both made of symmetrical achromats is saying... nothing, really- they're completely different in design.

    But don't be discouraged, much fun to be had. I'm sure weaker elements can be found.
    Bundles of vintage zooms can be had very affordably, you may need some tools to get the elements out (rubber bung, JIS screws, small flatheads) but worth your time in the long run. Easier when it's "one way"...
    just read that thread of yours, nice work! could any of these be mounted on a LF camera for close focusing without needing lots of bellows length, thus allowing for faster captures?

  9. #19

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    Re: Lens element sources and specs?

    Quote Originally Posted by Ethan View Post
    just read that thread of yours, nice work! could any of these be mounted on a LF camera for close focusing without needing lots of bellows length, thus allowing for faster captures?
    Yes - the benefit of any close up diopter is quicker exposure times. So they would work as you describe.

    Art Vaughan's Flickr has an extensive use and discussion of these for macro use, I would recommend you read there to see what works. I'd note only that he uses a few older lenses, and sometimes saws the front off.

    He notes how some suit certain lenses better than others.

    You should go as modern as you can afford when looking for lenses.

    For close up diopter use, 28-200 or 28-300 'superzooms' often contain a low dispersion element in their front group, aswell as being better corrected and decently sized.
    My Tamron 28-200 from the 90s is about 80mm FL, which might be a bit strong.
    There's no filter thread on the group, but it is self contained, so you could glue one on. Or you could take Art's approach and saw the front off.

    I mention these because they're often very affordable, 8-20, whether because electronic components fail or reputation for so-so image quality.

  10. #20

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    Re: Lens element sources and specs?

    I'm slowly learning to input patent data of lenses into programs like OSLO.EDU, so performance can be quickly estimated. Unfortunately, alot of the cheap third party ones are impossible to find patents for (nor are patents reflecting the produced item).

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