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Thread: Design Help for Wide Lenses?

  1. #1

    Design Help for Wide Lenses?

    Hello all!

    I am working on building a new 6x17 panoramic camera. Of course, to take advantage of the panoramic format, I want a wide angle lens. At first, I just thought I would just buy the lens, but due to lack of funds, I am not so sure that will be possible. I figured that maybe I would build my own photographic lens to save money, and learn something new in the process. I know a fair amount about optics (more than your average 15 year-old) but i fear that will not be enough.

    The dilemma I face is getting the optical system to provide adequate coverage of the film. Of course, wide angle lenses require a relatively short focal length to have a wide field of view. A short focal length single element optical layout the element would not be able to cover the entire image plane without severely vignetting the photograph. I could slap a 300mm objective lens on the thing and it could cover fine, but that is much too tele for my purposes. As I looked at lenses designed for wide angle/wide coverage (such as the metrogon) I noticed the curvatures of the front and rear elements is quite substantial. Is this the key to the coverage I need? I also noticed similar optical layouts of lenses like the hypergon and topogon (These designs can be found here: http://reference.findtarget.com/search/Large%20format%20lens/).

    To construct this lens I am willing to put effort into grinding, casting or buying optical elements. I am looking for tips for how to get the type of coverage i need, and yet retaining a relatively short focal length for the 6x17 format. If anyone could provide me with some insight or good resources to help me design and construct this lens, it is appreciated much more than you know.

    Thanks in advance,
    R. Callahan

  2. #2

    Design Help for Wide Lenses?

    G'day Ryan

    You've certainly set yourself a challenge.

    I'm no expert on lenses but I have learned a few things about simple lenses and home made cameras;

    - any unmounted lens element will pretty much cover any format

    - any lens may cause vignetting (by shading) because of construction issues, i.e. because of how the lens elements are mounted within the lens and how the lens as a unit is mounted to the camera

    - an extreme wide angle lens will cause vignetting (by fading) because the image making light has much further to travel to the edges than to the centre

    - a roll film camera is much harder to build with a focusing and viewing through the lens system than a sheet film camera, it may then be simpler to build a camera that focuses by hyperfocal means or pinhole, each of these three options give different results

    - home made cameras and optics can be built to give "perfect" results just like bought gear or they can be built to give less than perfect, unique, one off and truly beautiful results

    Seems to me that for a panorama camera you'd not actually need an extreme wide angle view because the image elements at the extremes of the image area would be too small. I'm thinking an angle of view of slightly wider than "normal" might be more pleasing.

    From what I understand about panoramic cameras some have lenses corrected to eliminate curvature distortions and then use a centre graduated filter to even out exposure. While other cameras use a not so wide angle lens that rotates and "paints" the image across the film plane to give an even exposure and no curvature distortions.

    See attached scans from one of my note books.
    Attached files

  3. #3

    Design Help for Wide Lenses?

    Thank you so much mr. Ray. Your help is definitely valued, and the notes are especially helpful. I think im going to use a pinhole plate for the camera until i get the camera perfected to my wants, then ill incorporate a lens.

    Keep an eye out for my camera building thread sometime in the (hopefully near) future!

    Thanks again.

  4. #4

    Design Help for Wide Lenses?

    Hi, about this argument i'm trying to build wide angle lens and i don't understand from what kind of lens i need.
    I explain better. I have some old lens, like Canon FD, and so. I think for make ray wide i can be use biconcave lens but it's very rare find it and if i try to use on my test box it do't work.

    Anyone know something about this?

    I hope i explained.

    Thanks a lot

  5. #5

    Design Help for Wide Lenses?

    Quote Originally Posted by 779
    I think for make ray wide i can be use biconcave lens but it's very rare find it and if i try to use on my test box it do't work.
    Hi, Mauro,
    If I understand correctly, you tried to use a bi-concave lens. You're right, that will not form an image. It would be a negative focal length lens, and the only way you will form a (real, on the film plane) image is with a positive lens. This will be convex on at least one surface, and if it is concave on one surface, that must be a shallower curve than the convex side. The net effect will be a lens that is thicker in the center than at the edges.

    Dave

  6. #6

    Design Help for Wide Lenses?

    Hello Ryan,
    What would be considered "Normal" for the 6x17 format is a lens of 180mm or 7 inch focal length as measured from the optical center or nodal point of the lens to the film plane. An affordable and available wide angle would be a Wollensak 6 1/4 inch 159mm f 9.5 lens. A relatively expensive and available but wider lens is the 4 3/4 inch 121 mm Angulon. With the 6x17 format you will need the similar covering capabilities as someone using the 5x7 inch film format. Although there are wider lenses than the above mentioned, the prices can be astronomically high and very hard to find. The 121 Angulon is the widest and most popular in use with the coverage you require. IF it is wide enough in coverage for you desires, the Wollensak 6 1/4" is a gem and affordable. It will even cover the 8x10 inch film format. If I wanted wider than these, I would use a pinhole of .350 to .400mm set 3 1/2 inches from the film plane.
    Hope this is of some value in your quest,
    Sam H.

  7. #7

    Design Help for Wide Lenses?

    I don't know how hard 6" Metrogons are to find these days, but they DO turn up...I have some in the original shutters which makes them monstrously large and impractical for some, I mean most projects.

    I also got for some purpose some day (as yet undefined), another Metrogon-design from Surplus Shed. It's fixed aperture no shutter. They didn't even know who the mfr was. In the past they have sold some Metrogon designs made by I think Fuji. This last one is weird in that it internally it has a lot of white paint instead of dead flat black...which really makes me curious why. I think it was $45 + their flat rate $5 shipping to anywhere in the US. If you're not stateside, that might be a moot point.

    I would have to dig up references, but could do so with some reminding to reply to you, for antique lens patents. I had looked at some of the early wide angle ones because there does seem to be something that defies most of my experiments...I have never stumbled upon an 'accidental' combination of found lens elements that in combination gave me a wide angle...but my experiments have been rudimentary and uniformed. One problem holding up a lens and a piece of ground glass is one can't see what happens at a small aperture that would probably be necessary due to the aperture required to see anything.

    A meniscus is a good bet if you can find a suitable f.l. Grinding my own is not a good idea for me. Again, Surplus Shed is where I scrounge my optics from.

    Murray

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