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  1. Re: What’s your most “unpopular” opinion about LF?

    As a lens designer… Most truths about optics that fly in the face of optical myths. I don’t remember specific examples, but it happens from time to time.

    -Jason
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    Re: Schneider-itis: The Perennial Problem

    NASA’s database for consumables:

    https://outgassing.nasa.gov/



    Low-outgassing materials meet two criteria:

    TML (Total Mass Loss) < 1%
    CVCM (Collected Volatile Condensable Materials) <...
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    Re: Schneider-itis: The Perennial Problem

    Assuming the lens designer is competent, the edges selected are based on
    1) stray light analysis to determine which edges cause artifacts
    2) balance contrast (sometimes too much isn’t wanted
    3)...
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    Re: Schneider-itis: The Perennial Problem

    We use sharpie at work when needed. Fun fact: Black sharpie is approved for edge blackening for space applications.
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    Re: Schneider-itis: The Perennial Problem

    Veiling glare is described in ISO 9358. It can be measured according to test in ISO 18844. The principles and practical measurements are described here: https://www.imatest.com/docs/veilingglare/...
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    Re: Schneider-itis: The Perennial Problem

    The lens designer chimed in above ;)
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    Re: Schneider-itis: The Perennial Problem

    Those are two different applications for mitigating stray light.

    Here we are talking about edge blackening of a lens, where the edge is ground and you want the pigment to flow into the...
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    Re: Schneider-itis: The Perennial Problem

    Definitely impacts contrast, yep.

    You would have to take the old stuff off with a soak in solvent (denatured alcohol or acetone), clean off the rest, then reapply. It is not easy to get it...
  9. Re: When do aspherically ground lenses date from?

    Polishing optical surfaces is as much craft / art as it is science and method. Before telescope making moved into proper shops, final polishing often took place at night under the stars, with the...
  10. Re: When do aspherically ground lenses date from?

    Foucault devised a tester to allow deterministic fabrication of aspheric surface for telescope mirrors in 1858. Before the Foucault tester was invented, aspherics were made but couldn’t be measured...
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    Re: Tilt, swing and the back nodal point

    They’re both correct.

    From Wikipedia:

    “ The nodal points are widely misunderstood in photography, where it is commonly asserted that the light rays "intersect" at "the nodal point", that the...
  12. Re: DIY ULF Lenses - 3D printing resin, epoxy casting or sand casting?

    Cost increases exponentially with diameter, so expect any build involving 20” refractive lenses - which would be near the upper limit — would be $100k - $250k as a very rough guess.
  13. Re: Making J Lane Positive Plates? (Famous Format Monobath?)

    For those interested, dry plate ambrotypes (emulsion coated black glass) are available as a regular product in 4x5, 5x7, 8x10, and 11x14 (other sizes enquire). The developer formula is posted on the...
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    Re: RIP William "WFW" Whitaker

    That’s terrible. I also shared many a conversation with Will. He was a very likable fellow. May he rest in peace.
  15. Re: DIY ULF Lenses - 3D printing resin, epoxy casting or sand casting?

    Such a lens can be designed of course, but the design form and thus the cost would depend on the focal length. The simplest/cheapest for a normal or portrait focal length would be a Cooke triplet...
  16. Re: DIY ULF Lenses - 3D printing resin, epoxy casting or sand casting?

    Qeb,

    I’d start by reaching out to Surplus Shed and asking if they have a meniscus lens in your desired focal length with a diameter capable of giving you an f/16 lens. Then, fabricate an f/22...
  17. Re: DIY ULF Lenses - 3D printing resin, epoxy casting or sand casting?

    Hi Kevin,

    I think you emailed me similar question but I think my reply bounced. So I’m glad you posted here so I can share my thoughts.

    This is not meant yo dissuade you in any way, but you...
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    Re: Lens element sources and specs?

    I use Zemax, as does most of the lens design world, so into Zemax format they will go.

    The prescriptions are, however, universally able to be manually typed into any design tool.

    -Jason
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    Re: Price of Film Going Up

    Ilford’s prices will likely increase as well, since the recent increases are due to material costs and supply issues.

    Compare price changes with long-term silver spot price trends, as an example.
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    Re: De Ionizing Air gun?

    Deionisers are commonly found on amazon at low cost. If you have a deionizing fan blowing across your workspace or constantly operating in your room, you will find dust isn’t as much of an issue any...
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    Re: Lens element sources and specs?

    I have an ongoing project to update the dioptrique prescriptions to zemax format. I’ve done most of the 1800s so far. There were a few minor corrections needed here and there.
  22. Re: Anybody used condenser lenses to build a taking lens?

    A condenser group simply renders the diverging output of the light source into a converging beam through the film plane, providing bright even illumination. The uniform illumination is accomplished...
  23. Re: Show your 3D printed LF photography related thing

    I have an SLA printer, so smokey black resin
  24. Re: Show your 3D printed LF photography related thing

    I converted a scan of a dry plate into an STL file and printed it out. The thickness was a function of grayscale. Here is the result.

    223546

    223547
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    Re: New articles by Jeff Conrad on DoF

    Thanks for bumping this thread up. There's some new optics guys at work since 2018 that I will forward this article to.
  26. Re: Question about Lenses and focal lengths... in German

    Pardon if I nerd out on the topic a bit.

    Dan, the 0.5 (in air) limit for f/#can be misleading, as the 1/2NA = f/# is a small angle approximation so it doesn’t truly indicate what the lens is...
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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. :D
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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...
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    Re: Lens element sources and specs?

    Couple of things:

    The original glass properties are not some long-lost mystery like Damascus steel or made from some super special ingredient like Himalayan salt. Magic doesn’t exist in the...
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    Re: Lens element sources and specs?

    It would be nice if it were that simple, but that’s not how lens design works. The errors which need to be corrected are on the order of wavelengths of light. That type of precision requires the...
  31. Re: The Problem with Modern Lenses.. transfered to those new to view camera image mak

    I suppose it depends on your definition: Marketing terminology or what designers identify as reliance on image processing to relieve the burden on the optics. I can tell you as an active,...
  32. Re: The Problem with Modern Lenses.. transfered to those new to view camera image mak

    Oh..very good question. Smart phone optics are an example of this, where image processing is used to enhance the image quality for display on a smart phone screen. This makes up in large part for...
  33. Re: The Problem with Modern Lenses.. transfered to those new to view camera image mak

    Optics aren’t designed by a computer. The drudgery of ray trace calculations is performed on a computer, but there is definitely a person designing those optics.

    The difference between optics...
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    Re: Turner-Reich modifications?

    ridax,

    I’ve gotten pretty good at repairing balsam separation in the Turner Reichs, and can confidentially say your first approach won’t work. In fact, it will cause the lens to adhere to the...
  35. Re: Gundlach Anastigmat 12" convertible hood size?

    They aren’t on the Anastigmat. Lens installs from the rear. The threads on that lens are primarily for control of stray light.


    Brian’s suggestion is your best bet, Paul
  36. Re: Regarding depth-of field curvature with tilt

    This all sound correct and good for how depth of focus / depth of field works. The analogous equations in the world of optical design typically get derived into determination of hyperfocal distance,...
  37. Re: A Heliar with an adjustable front group?

    In my humble opinion that seems like a hack job by a previous owner.
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    Re: Stearman Press SP-810

    Yes, that’s exactly what I do. Start at a slightly higher temp so that the average temp throughout development is exactly what it should be. It works well… I have a few examples in my media feed...
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    Re: Stearman Press SP-810

    Hey Kiwi,

    I’ve developed E-6 8x10 in it — Aerochrome too — and for E6 in general you have to be aggressive in your agitation. For the SP-810 I pick it up and slosh it around as much as I dare. ...
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    Re: Podcast with Sandy King

    It was a good podcast. Those guys are great.. the UK is turning into a nice little hotbed of “new” large format photography.
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