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  1. #1
    Alex Bishop-Thorpe's Avatar
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    Lens for 20x30": could I make one?

    I have an automatic roll paper easil for 20x30", and frankly I'll never use it as an easel. It was a $1 pickup only eBay auction, and works a treat, but I figure if you whack a lens on there you've got one giant camera for paper negs.

    So I'm looking for a lens that would cover 20x30", preferably at infinity but 1:1 would be alright too. I've done a bit of research into ULF lenses and most of them seem to be rare or expensive, but most of them are both. I'd prefer to keep this an affordable project, at least while I figure out if it'll even work. What are my options for making/finding a lens to cover this format? I dont mind single element, and the aperture doesnt matter too much to me as it would all be under artificial light. If al else fails I'll just go with a pinhole, but a lens would be preferable.

    So, tinkers, chime in. Are there some books I should look into? What is the main factor that determines the image circle of a lens? Would it be out of the question to have something like this fabricated?
    The Analogue Laboratory, or 'so you built a darkroom in an old factory in the industrial zone'.
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  2. #2

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    Hmm... not sure.. but for 20x24 you for example have
    19" Dagor
    30" Artar
    30" dagor
    35" Artar
    42" Artar
    550
    750 Apo-Germinar
    1100 Schneider XXL

    but i have no clue if any of them will cover 20x30, also you might want to look into the Ilford positive paper, http://www.ilfordphoto.com/products/...graphic+Papers

    Does anyone know a source/homepage that list lenses and what they cover?

    cool project, keep us posted

  3. #3
    Rick A's Avatar
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    How about a simple meniscus lens on a nested box arrangement ala Joe VanCleave.
    Rick A
    Argentum aevum

  4. #4

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    I also forgot...

    pinhole

  5. #5
    Alex Bishop-Thorpe's Avatar
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    I had been reading up on Meniscus lenses as a nice affordable option, but I had no clue what size to look for in order to get the coverage I'm after. In the mean time, I'm cannibalising an old overhead projector for bits to play with.

    sandholm, thank you for the list, I've also found that a few of the longer Rodenstock Apo-Ronars (600mm+) could suit my needs too. They're actually not as espensive as I expected either.
    The Analogue Laboratory, or 'so you built a darkroom in an old factory in the industrial zone'.
    Blog thing!.

    Worry less. Photograph more.

  6. #6
    richard ide's Avatar
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    At infinity, you would need around 36" focal length. At 1:1 a 24" focal length would cover. I would suggest process lenses like Apo Nikkors, Artars or Apo Germinars. These sometimes go for very low cost on auction sites. Image quality is superb. I am afraid you would have to provide more details for a tripod recommendation. ;<)
    Richard

    Why are there no speaker jacks on a stereo camera?

  7. #7

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    Quote Originally Posted by Fleath View Post
    sandholm, thank you for the list, I've also found that a few of the longer Rodenstock Apo-Ronars (600mm+) could suit my needs too. They're actually not as espensive as I expected either.
    no problem, the good thing with these lenses are that they are coming down in price. Personal I have used Schneider 550/11 XXL Fine Art and a 1100 XXL on a 8x20 camera which i then contact printed using the platinum process and the result from thous lenses are stunning. Still, i do believe they are around $5000 new.... so not exactly free...

  8. #8
    Nicholas Lindan's Avatar
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    For paper negatives almost anything - including a pinhole will work.

    A No. 1 close up lens has a focal length of 1 meter and will cover (I think -- you need an image circle of 900mm). Place the stop in front of the lens, with the concave side of the lens facing the subject. For extra resolution you can go the achromat route with either a 2-element close-up lens or something from Anchor optics.

    You can combine a lens with a pinhole - the combination sharpens the image considerably but keeps the pinhole's 'infinite' depth of field.

    If you want a process lens there is no reason getting anything fancy. A Brown or Ilex will provide more performance than you will need. However, process lenses are made for ~1:1 work and their coverage angle is small so you are going to need a really long one. And it is going to be huge and heavy. I have a 24" Dagor and it weighs about 10 lbs., making the lens support a major bit of work. Conversely, a close-up lens weighs an ounce at most.
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  9. #9

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    Surplus Shed is your friend. Check out the educational lenses as well as their fine lenses.

  10. #10
    michaelbsc's Avatar
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    If you can find an ancient overhead projector the lens in that may work. The ones I remember from grade school were monstrous, and the image field was monstrous, too.

    (Not that I understood image field in grade school. But in my memory it was pretty big.)
    Michael Batchelor
    Industrial Informatics, Inc.
    www.industrialinformatics.com

    The camera catches light. The photographer catches life.

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