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Thread: Lens coverage.

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    laz
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    Lens coverage.

    I know where to find the image circle size for modern and many older LF lenses. But is there a way, knowing focal length to calculate, however roughly, the coverage for an unknown lens?

    (I can't be asking Jim Galli about every lens I see all the time!)
    [SIZE=1]I want everything Galli has![/SIZE]
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    Paul Sorensen's Avatar
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    I think you would need focal length and angle of coverage. There are those who will know based on lens design, but that means that you need to be like Jim Galli and know just how all those old lenses are construted. We don't want that, do we?

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    laz
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    Quote Originally Posted by Paul Sorensen
    but that means that you need to be like Jim Galli and know just how all those old lenses are construted. We don't want that, do we?
    I live and breath to become more Galli-like every day!
    (actually I just think it's tacky to ask Jim to provide info on lenses he'll likely be bidding against me for on ebay!)
    [SIZE=1]I want everything Galli has![/SIZE]
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    How unknown?

    If you know the lens design a little math will give you the possible coverage.

    2 X the focal length X tan(angle of coverage/2)

    Simple if you know the angle and have a calculator. OTOH it's only telling you what the design should do.

    If you have the lens name and other info then google is your friend. If just a web search doesn't find it then click on groups. If neither of those finds it the lens likely doesn't exist-) Or you typed something wrong.

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    Quote Originally Posted by laz
    I know where to find the image circle size for modern and many older LF lenses. But is there a way, knowing focal length to calculate, however roughly, the coverage for an unknown lens?

    (I can't be asking Jim Galli about every lens I see all the time!)
    No. Coverage depends on the lens' design and on what you mean by coverage. For examples of widely-differing views on what coverage means, look at eBay listings for LF lenses.

    Sorry,

    Dan

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    laz
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    Quote Originally Posted by Nick Zentena
    If you know the lens design a little math will give you the possible coverage.
    2 X the focal length X tan(angle of coverage/2)
    Simple if you know tangle and have a calculator. OTOH it's only telling you what the design should do.
    ,
    Nick, Okay. So take the Goerz Dagor 10 3/4 inch series III, f:6.8 listed for sale here on APUG. Googling around I find that the Dagors have a 47 degree angle of coverage. I know the best thing would be to find this specific lens, but I plug in the numbers, 47 degree angle of coverage, 270 mm focal length, and get:

    540 x 0.4244748162096 = 230mm

    Correct?
    [SIZE=1]I want everything Galli has![/SIZE]
    [SIZE=1]I want to make images like Gandolfi![/SIZE]
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    Quote Originally Posted by laz
    ,
    Nick, Okay. So take the Goerz Dagor 10 3/4 inch series III, f:6.8 listed for sale here on APUG. Googling around I find that the Dagors have a 47 degree angle of coverage. I know the best thing would be to find this specific lens, but I plug in the numbers, 47 degree angle of coverage, 270 mm focal length, and get:

    540 x 0.4244748162096 = 230mm

    Correct?
    Close, but 0.4244748162096 is = Tan(23). Tan(23.5) = .43481237...

    Thus 234.7987mm
    Tom Hoskinson
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    laz
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    Quote Originally Posted by Tom Hoskinson
    Close, but 0.4244748162096 is = Tan(23). Tan(23.5) = .43481237...

    Thus 234.7987mm
    I should know better than to try my in the ballpark calculations here!
    [SIZE=1]I want everything Galli has![/SIZE]
    [SIZE=1]I want to make images like Gandolfi![/SIZE]
    rlazell@optonline.net

  9. #9
    David A. Goldfarb's Avatar
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    And just to make life more complicated, coverage for a Dagor increases significantly at small apertures. 10-3/4" should cover 8x10" plus a little more at f:22 and smaller.
    flickr--http://www.flickr.com/photos/davidagoldfarb/
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    Dagor's generally will cover about 80 degrees. Not sure where you got the 47 number. The older Series III were usually good for about 82-perhaps 85 at f64. Do the math over with those numbers and you'll find out it should cover a 7X17 & 11X14 OK and an 8X10 handsomely.
    He is no fool who gives what he cannot keep..to gain that which he cannot lose. Jim Elliot, 1949

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