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Author Topic: Would a Contemporary Lens Have a Greater Depth of Field? John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 04-09-2007 04:15 PM                     "People were shimming Century gate shoe back in the "70's with business cards or beer can shims to get even focus. At that time it was due to abysmal build quality." Sam, are you sure it was build quality? In Lou Berggren's article in SMPTE Journal (err, excuse me, "SMPTE Motion Imaging Journal") about lenses, he talks about how Kollmorgen got complaints about soft focus on the right side of lenses in 1962, now understood to be from the film bulging due to heat and not lying flat in the film plane, and how UA solved the problem with a a 0.002" (+/- 0.001") brass shim to balance the soundtrack. (There was also a problem with soft focus in the corners, for the same reason, but obviously not correctable so easily.) [Berggren, Glenn. "The Evolution of the Cinema Lens--Part 2: The Cinema Revival: 1962-1974." SMPTE Motion Imaging Journal, Feb/March 2007. Vol. 116 No. 2/3, pp. 87-103] The article also has this amusing anecdote (p.95): quote: Projectionist's Outlook The projectionists, coping daily with the focus problem and having no applicable lens data, invented their own "junk science." First, they attributed the right-side focus problem to "crooked lens grinding." Yet, turning the lens in the lens mount, usually showed that crooked was not the problem. It's a fun read (Part I was published in Dec. 2004, and to me, was not as interesting). Steve G. mentions, "Of the old lenses, the BX163s are pretty bad as lens go (they are the black ones and have maybe 4 elements in them...I'd have check on that to get exact specifications. ." You're right. According to Berggren, "the low-resolution 4-element BX 163 was a pre-1946 design," with the subsequent series being "the 6-element BX 241 f/1.9 series (in gold) designed between 1947 and 1952," and the "hybrid 7-element BX 290 f/1.7 series in 1954." I think the BX163 is an f/2.0 lens. I think maybe the big shocker for me was to learn that Kollmorgen sold its projection lens business to Schneider in 1973. I had not realized! --jhawk  |  IP: Logged Bill Enos Film God Posts: 2081 From: Richmond, Virginia, USA Registered: Apr 2000 posted 04-09-2007 08:08 PM                     Seems like we could hardly do worse than these BX 163s, yep, they are F2.0. The good part is that we didn't buy 'em, they have been here since the '50s and this operation inherited them from the previous owners...I guess we'll replace them when it's possible. Anybody got some good, inexpensive replacements? Did they recognize them for being this bad when they were new? If they were, why did anybody buy them, were they cheap or was there nothing better?  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 04-09-2007 11:01 PM                       Interesting stuff. I saw a lot of instances where the bottom and top of the image were not in focus at the same time. The lens mechanism and gate were one assembly and not pinned so it was very possible for it to be cocked with reference to the trap.  |  IP: Logged Robert Throop Master Film Handler Posts: 412 From: Vernon, NY USA Registered: Jun 99 posted 04-10-2007 01:29 PM                     quote: John Hawkinson the low-resolution 4-element BX 163 was a pre-1946 design While this is true, Kollmorgan continued to make the BX 163 well into the 1960's. They were frequently used in long throw situations with older projectors that wouldn't accept 4 inch diameter lenses. I have a pair with an E.F. of 8.5 inches and I'm sure they were made in even longer focal lengths. Bob  |  IP: Logged

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