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Thread: DIY Meniscus

  1. #11

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    The Greene book has some rough estimates of coverage for a given type of lens based on the diameter and focal length. If I remember, I'll bring the book in and scan a couple of pages for you.

  2. #12

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    Terence,
    Great, thanks. The lenses I am looking at are 50mm dia/250mm FL, and 60mm dia/235mm FL.

  3. #13

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    hi stephen

    you might look for an article that john siskin wrote for view camera a few years back. it was all about what you want to do. he got his lens optics from anchor optical ( i think?) and he was using a tin can as a barrel ...

    i can't remember when it was -- 2 maybe 3 years back ... if i can dig it up i'll make a copy for you and send it your way ...

    john
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    PM me for details

  4. #14
    Mark Fisher's Avatar
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    If you want to stretch a little, you could do a compound symmetrical. I just finished one this weekend (I used a modified version of the method from Primitive Photography). A few dollars in PVC pipe, black paint plus about $10 in lenses (2l enses, 50mm dia and about 500mm focal length) from Anchor Optical. The end focal length should be around 250mm. These lenses are scratched, but I suspect that won't matter too much. I'll write up something once I am done with the experiment (I also have about a 2 Lb 8x10 camera to go with it!).

    Mark

  5. #15

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    Mark,
    I look forward to seeing your report. I want a meniscus for the look, as I really am going for a portrait type of lens.
    I drew up some plans this afternoon real quick, and will toss them into CAD later. Being as I ordered two sets of lenses with different diameters, I figure I will make the barrel to fit the larger lens, then I can set the smaller diameter lens in a thicker bushing to thread into the barrel. Also, I can just make another aperture wheel (for the other focal length) to fit the same barrel. This will save me from making two barrels, being as large pieces of brass aren't cheap.
    On the original oldies, how did they seal the area between the aperture wheel and the barrel ? Is it just a tight tolerance, or did they put a piece of felt, etc to seal it ?

  6. #16

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    All,
    Here's a quick drawing I came up with earlier. My dxf-jpg converter sucks, so I have two drawings here (its hard to see the plan w/dimensions in black/white only).
    As it sits now, its setup as a 235mm f/5. Im not sure if Im going to put in a wheel type of aperture change, or if I can make some 'thimble' type of stops that would insert into the barrel (ala Imagon). I need to take a look at some designs that use a rotary type of stop, as Im not quite sure 'how it works' yet.
    Last edited by SteveH; 08-01-2006 at 04:38 PM. Click to view previous post history.

  7. #17

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    Meniscus? Looks bi-convex to me. Please clarify. Do you mean "single element" when you type meniscus?

  8. #18
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    isnt meniscus the same as in disposble cameras?
    Marko Kovacevic
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  9. #19

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    Greene suggests using :
    [A] A focal length equal to 0.828 x Film Diagonal.
    [B] A lens diameter equal to 1/5 to 1/7 of the focal length.
    [C] A stop of between f/16 and f/32, located 1/6 to 1/7 of the focal length in front of the lens.

  10. #20

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    Quote Originally Posted by Dan Fromm
    Meniscus? Looks bi-convex to me. Please clarify. Do you mean "single element" when you type meniscus?
    Dan,
    We're both right I believe. A meniscus can be either singular, or achromatic. Either way, I have seen the doublet called a 'meniscus' in various texts.
    I would have been more specific in my title, but when I wrote the first post, I was not sure if I wanted to go with an achromat or not.

    Quote Originally Posted by TERENCE
    If I remember right, the achromat seems the way to go as you don't have to adjust after focusing to allow for the difference between "optical focus" and "chemical focus."
    I looked more into that, and decided that it was the way to go.

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