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  1. Re: Disassembling Voigtlander Apo-Skopar process barrel lens

    I’ve dealt with crimping before. Slow and steady works.

    I’ve tried strap wrench, there’s not enough “meat” to grab on to. PB blaster’s been stewing for a few days.

    I think I’ll make a...
  2. Disassembling Voigtlander Apo-Skopar process barrel lens

    A photographer sent me a Voigtlander Apo-Skopar 45cm f/9 process lens that needs balsam separation repaired.

    Rear group unscrews just fine, but I cannot get the front group disassembled. Does...
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    Re: Glass Dressing or coating for old lenses

    *scans through thread*

    *shudders*

    *backs out slowly*
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    Re: Lens surface issue.

    Fungus damage to coatings. Shoot it and see what you think. Impact to imagery will be minor.
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    Re: Interest in a new Hypergon?

    Not yet. I wanted to get the lenses squared away before tackling the custom apodizing filter, since I'll need to invest a bit more $$ to get it designed and prototyped. I'm currently talking to...
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    Re: Interest in a new Hypergon?

    Just received proof of concept lenses from the shop (8x10 format), so I mounted them in a 3D printed test barrel.

    The fellow who approached me with the project backed out, but I’m considering...
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    Re: Is focus a plane to plane affair?

    I’m not dead yet, Drew. And I still design optics. ;) This time as head of the engineering department at the country’s largest optical shop.
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    Re: Interest in a new Hypergon?

    I will be able to report when the alpha prototype is assembled in a couple weeks.

    Originals are focused at f/22 and shot at f/32-f/45. That will be the case for these.
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    Re: Is focus a plane to plane affair?

    Oh of course. Curvature in one axis has been around since the Brownie cameras, and observatory grade Schmidt telescopes had vacuum backs for lining up film with the curved field.

    Every so...
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    Re: Hung Up On “Default” Apertures?

    Interesting thought, John. I often -- though not exclusively -- shoot in the f/8 - f/11 region. I think that comes down to personal preference. I enjoy the effect of depth of field, lens...
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    Re: Is focus a plane to plane affair?

    Bernice, you’re too intelligent to ask a question like that.

    BTW, I’ll be in your neck of the woods at the end of this month, at Photonics West.

    -Jason
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    Re: Is focus a plane to plane affair?

    not quite. This is why lens designers speak in terms of “surface of best focus”. This surface is not inherently flat. Field curvature correctly implies that different field angles focus at...
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    Re: Interest in a new Hypergon?

    Bernice that’s a good point. I’ll suggest to the customer an option would include a custom superwide body for those who need it. Hugo, it’d be interesting to know whether Chamonix could do a run of...
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    Re: Interest in a new Hypergon?

    You can calculate from the focal lengths that we're producing the 135 degree variant. Narrower than that is not interesting. Re: the star diaphragm: Read second paragraph of OP.



    We've poked...
  15. Re: A Modest Contribution to Dispelling Diffractiophobia

    I must admit having never worried about diffraction limit for photography (work is a different story). For me the stop setting is determined by what I want for depth of field.
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    Re: Interest in a new Hypergon?

    Ah gotcha. :)
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    Re: Interest in a new Hypergon?

    Corran, I wouldn’t be making a complete camera, just the lens. As a lens designer, I have no interest in producing complete cameras. I would, however, put a bug in Steve Lloyd’s ear, since I’ve...
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    Re: Interest in a new Hypergon?

    The focal lengths are..

    4x5: 38mm
    8x10: 75mm

    Dig out the recessed lens boards and drop that front rail. :D

    As for larger formats.. they are possible, albeit not as a concurrent...
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    Re: Interest in a new Hypergon?

    The Metrogon and Topogon (both the same design) maxxed out at 100 degree Field of View. This didn't come close to the 135 / 140 degree field of view of the Hypergon. They traded FOV for speed. The...
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    Interest in a new Hypergon?

    Hey folks, I was approached by a fellow large format enthusiast about bringing a new Hypergon lens to market in 4x5 and 8x10 format. If you don't know what a Hypergon is, you really should. It is...
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    Re: removing lens coating ???

    I’m not yet set up to strip coatings after moving.

    In any case, knowing what I do about how coatings work and what they get you in the UV, removing them will still result in a net loss of...
  22. Re: Eastman Ektar 14 inch: serial number and coating

    Single-layer coatings in the visible spectrum all use Magnesium Flouride. The low index of refraction of MgF2 is what provides the benefit in reduced reflections at the air-glass interface. ...
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    Re: My Cycle Poco 5x7 is Very Excited...

    A quick point of correction: Glass plates in general have always focused the same distance as film. Or to more correctly say: the standard depth for a given format from the mounting surface of a...
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    Re: Dry Plate Availability

    Alan, I wasn’t sure if you had received my reply to your email but looks like you did. I’m guessing you could detect my frustration with myself at not being able to produce dry plates as soon after...
  25. 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...
  33. 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...
  34. 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...
  36. 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.
  37. 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.
  39. 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...
  40. 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...
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