Lens coverage.

Discussion in 'Large Format Cameras and Accessories' started by laz, Oct 25, 2005.

  1. laz

    laz Member

    Messages:
    1,118
    Joined:
    Aug 3, 2005
    Location:
    Lower Hudson
    Shooter:
    Multi Format
    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!)
     
  2. Paul Sorensen

    Paul Sorensen Member

    Messages:
    1,897
    Joined:
    Nov 15, 2004
    Location:
    Saint Paul, MN
    Shooter:
    Multi Format
    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? :D
     
  3. laz

    laz Member

    Messages:
    1,118
    Joined:
    Aug 3, 2005
    Location:
    Lower Hudson
    Shooter:
    Multi Format
    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!)
    :smile::smile::smile:
     
  4. Nick Zentena

    Nick Zentena Member

    Messages:
    4,679
    Joined:
    Nov 21, 2004
    Location:
    Italia
    Shooter:
    Multi Format
    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.
     
  5. Dan Fromm

    Dan Fromm Member

    Messages:
    4,133
    Joined:
    Mar 23, 2005
    Shooter:
    Multi Format
    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
     
  6. laz

    laz Member

    Messages:
    1,118
    Joined:
    Aug 3, 2005
    Location:
    Lower Hudson
    Shooter:
    Multi Format
    ,
    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?
     
  7. Tom Hoskinson

    Tom Hoskinson Member

    Messages:
    3,879
    Joined:
    Mar 7, 2004
    Location:
    Southern Cal
    Shooter:
    Multi Format
    Close, but 0.4244748162096 is = Tan(23). Tan(23.5) = .43481237...

    Thus 234.7987mm
     
  8. laz

    laz Member

    Messages:
    1,118
    Joined:
    Aug 3, 2005
    Location:
    Lower Hudson
    Shooter:
    Multi Format
    I should know better than to try my in the ballpark calculations here! :smile:
     
  9. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

    Messages:
    17,942
    Joined:
    Sep 7, 2002
    Location:
    Honolulu, Ha
    Shooter:
    Large Format
    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.
     
  10. jimgalli

    jimgalli Subscriber

    Messages:
    3,571
    Joined:
    Sep 7, 2002
    Location:
    Tonopah Neva
    Shooter:
    ULarge Format
    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.
     
  11. laz

    laz Member

    Messages:
    1,118
    Joined:
    Aug 3, 2005
    Location:
    Lower Hudson
    Shooter:
    Multi Format
    One of the things I'm just loving about LF are these sorts of details that as you say, make life more complicated!

    I am especially intrigued by old lenses and what they can do. No offence intended to the 35mm crowd (of which I'm still a member) but 35mm seems so cookie cutter compared to LF where the almost endless variables ensure a unique photo every time (maybe a bad one, but it will be uniquely bad!)

    I've sprung for a CD of The Lens Collectors Vade Mecum. I guess I'm a totally lost soul now!

    -Bob
     
  12. laz

    laz Member

    Messages:
    1,118
    Joined:
    Aug 3, 2005
    Location:
    Lower Hudson
    Shooter:
    Multi Format
    Oh boy, must be stupider than usual today! I lost track of where or what I was reading. It was Goertz Red Dot Artar that I had read had a 47 degree angle!

    (My first attempt and I've embarrassed myself before the great Galli! :smile:)

    Thanks Jim!

    -Bob
     
  13. Dan Fromm

    Dan Fromm Member

    Messages:
    4,133
    Joined:
    Mar 23, 2005
    Shooter:
    Multi Format
    The Great Galli? Cousin of the Great Oz? Nicer guy, though, than Oz was before the great unmasking.
     
  14. Tom Hoskinson

    Tom Hoskinson Member

    Messages:
    3,879
    Joined:
    Mar 7, 2004
    Location:
    Southern Cal
    Shooter:
    Multi Format
    It's Curtains for you, Dan - focal plane, of course!