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Thread: A DIY 123mm f/8 Cooke split triplet for 4x5

  1. #11
    Nodda Duma's Avatar
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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Dan I looked at COTS lens designs which would need meniscus lenses. Meniscus COTS lenses are rare and the right set that would be needed don’t exist unless something has changed in the past 2-3 years.

    I was, however, able to sneak one token COTS lens into a $50k 3-lens imaging system at work.
    Newly made large format dry plates available! Look:
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  2. #12

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Jason, you stinker, I had to look up COTS. Commercial Off The Shelf. I'm not surprised that ones that could be used to make an imitation Wide Field Ektar don't exist. Old economist test of feasibility: if it is worth doing and can be done, someone somewhere is doing it.

    I took a quick, possibly incompetent. look at Edmund's on-line catalog (just a coupla' miles away, until it closed I visited their surplus room fairly often) and found no meniscii. Surplus Shack has + and - meniscii, with practically no specs given in the catalog. Didn't look at Thorlabs.

  3. #13
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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Dan that made me chuckle. For future reference, GOTS = government off the shelf GFE = government funded equipment.

    Thorlabs has a very few…all the wrong shape for minimizing spherical aberration.

    Last time I met their regional rep, I considered suggesting they stock singlets that are useful for imaging designs. But, had other things to discuss so it never came up.
    Newly made large format dry plates available! Look:
    https://www.pictoriographica.com

  4. #14

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    I agree - I tried a few designs with the Thorlabs' meniscus lenses and unfortunately wasn't able to get anywhere.

    Here's an updated optical design that achieves similar performance at f/6.7. I swapped out the two inner plano convex N-BK7 lenses for CaF2 versions. The engineer in me is sad that this new iteration was achieved by trial and error rather than any particular design insight.

    Effective focal length: 164.6 mm. Sharp across the field (150mm image diagonal) at f/6.7. Vignetting is less than before, with about 65% relative illumination in the corners. Unfortunately, the CaF2 lenses cost quite a bit more; the total lens cost is $1k. The CaF2 lenses also don't come anti-reflection coated, same as the fused silica bi-concave lens. Also not a wide-field lens - the 150 mm diagonal corresponds to an angular field of view of 48.4 degrees.

    Click image for larger version. 

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    LA1353-A
    5.76 mm gap
    LA5230
    16.52 mm gap
    LD4735
    3.25 mm gap
    STOP
    16.00 mm gap
    LA5220
    1.00 mm gap
    LA1353-A
    Back focal length: 131.08 mm

    Again, here's the source bitmap and resulting simulated image.

    Click image for larger version. 

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    Click image for larger version. 

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    Any comments about suitability for LF photography are appreciated. My suspicion is that $1k is getting pretty steep for just the lenses in a DIY project, so I think I'll go back to figuring out a mounting arrangement to share for the 123mm f/8 design.

  5. #15

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Quote Originally Posted by OTS Matt View Post
    Any comments about suitability for LF photography are appreciated. My suspicion is that $1k is getting pretty steep for just the lenses in a DIY project, so I think I'll go back to figuring out a mounting arrangement to share for the 123mm f/8 design.
    The big question is what y'r new confection (no sarcasm intended) does better than currently available normal +/- lenses for 4x5, especially at the shooting apertures normally used. Most of us rarely shoot wide open because of depth of field and coverage considerations.

  6. #16

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Quote Originally Posted by Dan Fromm View Post
    The big question is what y'r new confection (no sarcasm intended) does better than currently available normal +/- lenses for 4x5, especially at the shooting apertures normally used. Most of us rarely shoot wide open because of depth of field and coverage considerations.
    Good question! I doubt these stock lens systems will ever be better than what you could achieve with custom optics, but they can be pretty good if you really want to DIY. Perhaps the better question (and maybe the subject of a different thread) is: what would be worth building yourself because it's not otherwise available?

  7. #17

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Quote Originally Posted by OTS Matt View Post
    Good question! I doubt these stock lens systems will ever be better than what you could achieve with custom optics, but they can be pretty good if you really want to DIY. Perhaps the better question (and maybe the subject of a different thread) is: what would be worth building yourself because it's not otherwise available?
    From time to time people here have looked into custom optics, usually for wide angle lenses for formats larger than 8x10. So far the costs have been prohibitive.

    As for making something because it isn't available, see above. More seriously, used lenses for formats no larger than 8x10 are around, often at reasonable prices, and with more than enough coverage at focal lengths from a bit less than 0.4 x normal to longer than easily usable. To give you an idea, look at the lens catalogs to which the link in the first post in this https://www.largeformatphotography.i...mainly)-lenses discussion points.

    Also remember that photographers have been somewhat specialized for quite a long time. They take pictures -- the artsy types capture images, I don't see the difference between that and taking pictures -- using off-the-shelf equipment. Very few photographers design and build equipment. Most of the very few go no farther than making view cameras, which aren't that much more complex than boxes (ducks and runs).

  8. #18

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    If you can build something like this, I think many 810 camera users will be interested. Something with 100 degree coverage.

    https://www.ebay.com/itm/114788016899

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Quote Originally Posted by Hugo Zhang View Post
    If you can build something like this, I think many 810 camera users will be interested. Something with 100 degree coverage.

    https://www.ebay.com/itm/114788016899
    Hugo, some years ago Michael Kadillak tried to persuade an optical shop to make such a lens -- they told him that they didn't want to just make a Dagor type, they could make something better -- and to organize a group buy. The economics -- cost of producing as many as Michael thought he could shift at the cost of production -- didn't come close to working.

    But why be a piker? Why not go for a high coverage lens for larger formats? Don't settle for a Dagor when there's the f/14 Perigraphe VIa. Thinking of which, the longest focal length cataloged was 800 mm, claimed coverage 2 meters at infinity. Just what's wanted for shooting 1.2 x 1.6.

    Also remember that the OP has been talking about making useful photographic objectives composed of commercial off-the-shelf lenses. This is in some ways a harder problem than making custom optics, especially with w/a lenses.

  10. #20

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    Re: A DIY 123mm f/8 Cooke split triplet for 4x5

    Quote Originally Posted by Dan Fromm View Post
    To give you an idea, look at the lens catalogs to which the link in the first post in this https://www.largeformatphotography.i...mainly)-lenses discussion points.
    Thanks Dan. This looks like a great resource that you've assembled and maintained!

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