Page 1 of 11 123 ... LastLast
Results 1 to 10 of 101

Thread: The Computar lens and ULF coverage.

  1. #1

    Join Date
    Sep 2003
    Location
    South Carolina
    Posts
    5,107

    The Computar lens and ULF coverage.

    I now have had the opportunity to measure coverage of three different Computar lenses, 210mm, 240mm and 300mm. All give coverage of close to 95 degrees. Specific coverage in mm is as follows. The measurements were made on the ground glass of my 7X17 and 12X20 cameras with the lenses focused at 50 feet and could be off by a few mm.

    210mm Computar, 456mm

    240mm Computar, 523mm

    300mm Computar, 655mm

    Though not tested the 270mm Computar should cover about 590mm.

    By contrast I have never seen or heard of a Kowa Graphic lens that will cover much more than 80 degrees. From this I must conclude that these are not the same lenses at all, or if they are the glass of the Kowas is installed in such as way that results in mechanical vignetting. I have never had an opportunity to examine a Kyvytar so I can not say how they compare to the Computar.

    To figure out which Computar you would need for a specific ULF format note the following coverage requirements below. This is for the actual image of the negative, slightly smaller th an the theoretical diagonal of these formats.

    11X14 450mm

    7X17 460mm

    8X20 540mm

    12X20 585mm

    So, we find that the 210mm Computar covers 11X14 with just a tad to spare and just misses the corners on 7X17 by a few mm. The 240mm Computar covers 7X17 with movement, and the 300mm Computar covers 12X20 with almost three inches of movement. and in theory the 270mm Computar should cover 8X20 with movements and just hit the corners oin 12X20.

    I offer this information in an effort to clear up some of the confusion about Computar/Kowa/Kyvytar lenses and in the hope that more ULF workers will discover and use these wonderful lenses. In many ways they are truly unique and provide coverage for the size that simply is not available in any other design, regardless of price. They share some characteristics with Dagors but the circle of illumination of the Computar is not only about 10 degrees larger than the Dagor, but performance at the edge of the field is much superior.

    Now I have got to go find a 270mm Computar!! And if anyone has specific design information about these lenses I would be very appreciative if you would provide me with the source.
    http://www.sandykingphotography.com/
    For discussion and information about carbon transfer please visit the carbon group at Yahoo.
    https://groups.yahoo.com/neo/groups/...nTransfer/info

  2. #2
    tim atherton's Avatar
    Join Date
    Jul 1998
    Posts
    3,693

    The Computar lens and ULF coverage.

    very useful stuff Sandy.

    What aperture was that all done at? And were they barrel mount or shutter? (with the Kowa 210mm there is some mechanical vignetting when the lens is barrel mounted)

    thanks
    You'd be amazed how small the demand is for pictures of trees... - Fred Astaire to Audrey Hepburn

    www.photo-muse.blogspot.com blog

  3. #3

    Join Date
    Sep 2003
    Location
    Harbor City, California
    Posts
    1,748

    The Computar lens and ULF coverage.

    Thank you for your worthwhile work. I hope more people will follow your good example.

  4. #4

    Join Date
    Oct 2003
    Location
    North York, Ontario
    Posts
    95

    The Computar lens and ULF coverage.

    Sandy, FWIW I had an Apo Kyvitar 240mm for a short time and was able to use full rise on 8x16 (IC ~450mm) without any problem. That particular lens was also a 'convertible' (converted to something like 420mm).

  5. #5

    Join Date
    Sep 2003
    Location
    South Carolina
    Posts
    5,107

    The Computar lens and ULF coverage.

    Tim,

    I used f/22 in looking at the image on the ground glass. However, I feel reasonably sure that you would have to stop down to f/32 or f/45 for optimum performance across a field this large. In any event over 95% of the negatives I make with 7X17 and 12X20 format are made at F/45 or f/64. Of course, as you know stopping down a lens improves performance at the edges but doe not increase the actual size of the circle of illumination.

    The 240mm and 300mm lenses were checked in a Copal #3 S shutter. I looked at the image of the 210mm lens in its barrel mount.

    Which brings me to a question. With the 240mm lenses I have something that appears to be a spacer of about 0.060" thickness, but I don 't have one for the 210mm lens. I notice on the 300mm lens, which I purchased already mounted in a Copal 3 S shutter, that the spacer is installed between the shutter and the rear element and obviously increases separation between the front and rear elements. Does anyone know the purpose of this spacer? Is it to correct for infinity focus when using the lens in a shutter? Or is it to correct for a discrepancy between spacing in the barrel and shutter? I am speculating that without the spacer the coverage of the 210mm would be slightly greater but am concerned that performance may not be as good.
    http://www.sandykingphotography.com/
    For discussion and information about carbon transfer please visit the carbon group at Yahoo.
    https://groups.yahoo.com/neo/groups/...nTransfer/info

  6. #6

    Join Date
    Sep 2003
    Location
    South Carolina
    Posts
    5,107

    The Computar lens and ULF coverage.

    "Sandy, FWIW I had an Apo Kyvitar 240mm for a short time and was able to use full rise on 8x16 (IC ~450mm) without any problem. That particular lens was also a 'convertible' (converted to something like 420mm)."

    Roger,

    That would certainly be similar in coverage to the Computar. In the back of my mind I remember someone else mentioning that they had a 240mm Kyvitar that covered 7X17, and I don't believe it was you, so it seems that the Kyvitars may cover like the Computars. But do all of them? And given the questionable lineage of these lenses it might also be presumptious to conclude that all Computars have 95 degree coverage. But the three I have tested all do, and to be a bit more specific, all three have serial numbers in the 500xxx.
    http://www.sandykingphotography.com/
    For discussion and information about carbon transfer please visit the carbon group at Yahoo.
    https://groups.yahoo.com/neo/groups/...nTransfer/info

  7. #7
    tim atherton's Avatar
    Join Date
    Jul 1998
    Posts
    3,693

    The Computar lens and ULF coverage.

    Again, another bit I copied from somehwere. How accurate it is - I don't know:

    "Many years ago, Burleigh-Brooks introduced a line of lenses under the name of Computar; the Kowa Lens Company of Japan made them. These lenses were a remarkable value as they were a wide-angle plasmat, excellent quality and quite inexpensive. After Burleigh Brooks folded, the lenses were briefly carried by Kyvyx and were called Kyvytar and then independently offered by Kowa a Kowa Graphic lenses, in both shutter and barrel."

    Presumably it would seem some changes in contruction/design occurred over that period?
    You'd be amazed how small the demand is for pictures of trees... - Fred Astaire to Audrey Hepburn

    www.photo-muse.blogspot.com blog

  8. #8
    Michael Jones's Avatar
    Join Date
    Nov 1998
    Location
    Nashville, Tennessee
    Posts
    507

    The Computar lens and ULF coverage.

    Sandy:

    The spacer is to adjust (optimize) the focus at a specific magnification. If you could find the View Camera article on the Doktor (sp?) Jena lenses of a few years ago, it explained how these process lenses are optimized for a specific focussing range and magnification and the cells are spaced accordingly with the "trimming" ring. For "landscape" work (focussing at infinity), I believe you remove the ring. Thanks for the comparison of the Computars.

    Mike
    “You can’t have everything. Where would you put it?”

  9. #9

    The Computar lens and ULF coverage.

    Sandy,
    Good stuff! Thanks for sharing the info. I'm currently looking for a compact lens in the 150mm - 165mm range for use on the 4x10 format. I just got a 159mm f12.5 Wollensak Extreme Wide Angle Raptar (a later coated sample in a Rapax shutter) and also have a 150mm f9 Graphic-Kowa in a barrel I plan to slip into a Copal No. 1 shutter. I haven't had a chance to shoot any tests with them yet. Obviously, the Wollensak will cover with room to spare, but I'm curious to see how the performance compares to my other newer multicoated lenses.

    Based on your results, and other posts I've read, it looks like the Computars cover about 95 degrees and the Graphic-Kowas about 85 degrees. If that's the case, the 150mm Graphic Kowa will hit the corners of 4x10, but leave very little left for movements. So, does anyone know if they made the f9 Computar in the 150mm focal length. I seem to see a lot of 150mm Graphic-Kowas, but don't recall seeing any f9 Computars shorter than 210mm.

    Other "similar" lenses that would be interesting to test would be the f9 Fujinon A series and f9 Germinar-W series. The Fujinons are rated to cover 70 degrees, but like many of these lenses throw a significantly larger circle of illumination. Problem is the corners get real soft at the extremes. For example, a 180mm f9 Fujinon A just BARELY misses hitting the corners of 8x10 (a VERY small amount of vignetting in the extreme corners), but the image (at f22) becomes too soft to be usable for anything larger than 5x7 with moderte movements. Perhaps it would sharpen up more (and actually hit the corners of 8x10) if I tried it at f45 or f64. Has anybody tried really pushing the coverage of the A series Fujinons? I use the 180 and 240 regularly on 4x5 and 5x7, but don't usually shoot anything larger. So, I haven't done any conclusive tests on large formats.

    The Germinar-W series is very interesting. It is a very compact (similar to Fujinon A and G Claron) f9 plasmat type lens. Don't confuse it with the much more common, larger, single coated APO Germinar-W series. The (plain) Germinar-W was the last series introduced by Docter Optic before they went out of business. Unlike the earlier APO Germinars and APO Germinar W models, it is also beautifully multicoated. The shorter focal lengths screw directly into standard Copal/Compur shutters. I have a little 150mm f9 Germinar-W for backpacking with the 4x5. I mounted it in a newer style Compur 0 and it weighs only 130g. I know it will cover 5x7, and probably 4x10 (the circl;e of illumination is large enough, not sure on the corner sharpness). If you can find any of the longer (240mm, 300mm, 360mm) Germinar-W lenses (good luck!), they would probably make excellent lenses for ULF use. If you ever do get any, please let us know how they compare to your Computars.

    Kerry

  10. #10

    Join Date
    Sep 2003
    Location
    South Carolina
    Posts
    5,107

    The Computar lens and ULF coverage.

    Tim,

    Thanks for that information. Any idea about time line on these events?

    I had pretty much concluded that the Computar had to be of Dagor or Plasmat (which is kind of a split Dagor) design, but it nice to have confirmation. That would mean they are of symmetrical design and could be used as convertibles, using the rear element alone, at about 1.75X the focal length of the combined elements. Be interesting to see how the individual cell will perform by itself.

    But I am curious why this particular lens, of all the Plasmat type processes lenses made, had some wider coverage than the others?
    http://www.sandykingphotography.com/
    For discussion and information about carbon transfer please visit the carbon group at Yahoo.
    https://groups.yahoo.com/neo/groups/...nTransfer/info

Similar Threads

  1. Computar 150mm coverage?
    By Donald Hutton in forum Cameras & Camera Accessories
    Replies: 2
    Last Post: 11-Mar-2006, 14:37
  2. 135 lens coverage
    By ronald moravec in forum Lenses & Lens Accessories
    Replies: 8
    Last Post: 14-Jul-2005, 23:12
  3. Computar enlarging lens
    By Richard Schlesinger in forum Darkroom: Equipment
    Replies: 2
    Last Post: 12-Jul-2005, 18:38
  4. Best guess Glennview's ~210mm ~F/8 lens that covers 11X14 is a Computar?
    By Donal Taylor in forum Cameras & Camera Accessories
    Replies: 8
    Last Post: 4-Jun-2004, 17:17
  5. Lens hood required when using large coverage lens on small format?
    By Bill Glickman in forum Lenses & Lens Accessories
    Replies: 1
    Last Post: 31-Jul-1999, 15:06

Bookmarks

Posting Permissions

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