Results 1 to 7 of 7

Thread: How do I guess the Angle of Coverage?

  1. #1

    How do I guess the Angle of Coverage?

    Hi,
    thinking about building a meniscus lens set with aperture cards. Found at Surplus Shed a positive meniscus lens, coated, with 42 mm diameter and focal lenght of 89mm. I need to cover 4x5 negs. Any formula to check if it will work?
    Thank you guys.

  2. #2
    500+ Posts earlj's Avatar
    Join Date
    Jun 2004
    Location
    Inver Grove Heights, Minnesota, United States
    Posts
    5,744
    Blog Entries
    7
    Project an image onto a white card, and you should be able to see the image circle size. You might have to create some darkness. Mount the lens in the side of a big cardboard box and then take your white card inside the box and focus the image on the card. You should be able to measure the focal distance as well as see the diameter of the image circle.
    because:
    "a squid eating dough in a polyethylene bag is fast and bulbous, got me?"
    -Don Van Vliet

  3. #3
    Ok then,
    it's workbench. No way of knowing it with math?

  4. #4
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522
    It's going to depend on the mount and housing of your lens and aperture stops. The lens, unmounted, will cover 4x5 but it's pretty wide angle, so the stop will need to be close to the lens to work.

    Diagonal of the format is sqrt( 4*4 + 5*5 ) inches then * 25.4 to get mm. About 163mm.
    Take half of that and use the "opposite over adjacent" rule from trigonometry to get:

    half the angle of view = arctan( 81.5 / 89 ) = about 42.5 degrees.
    So the field of view is about 85 degrees, which is pretty wide. A little wider than a 24mm lens on a 35mm camera ( my favorite lens! )

    Now, draw a picture of your lens and any tube it will be mounted in, and where the aperture will be. Draw lines coming in from 42.5 degrees in either direction and if they go through the lens and the aperture without hitting any obstruction it will work.

    Sounds like fun!
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  5. #5
    Thank you for the input! About 85 degrees over 4x5 is what I was hoping for... Holy Trigonometry Batman!

  6. #6
    500+ Posts Ned.Lewis's Avatar
    Join Date
    Jul 2012
    Location
    Sonoma County, California
    Posts
    522
    Quote Originally Posted by Ricardo de Oliveira View Post
    .. Holy Trigonometry Batman!
    ..........
    Some photos: Ipernity
    ( pinholes and solargraphs mixed in among the rest)

  7. #7
    Quote Originally Posted by Ricardo de Oliveira View Post
    Holy Trigonometry Batman!
    To which I have to point out that the entire 1966+ Adam West Batman series will be released on Blu-Ray in early November.
    ~$175 on Amazon, but as it's the one and only Real Batman...

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •