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Author Topic: 35mm lens on 16mm projector. Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 05-21-2012 06:45 PM                     I'm not sure if I have a unique issue here, but I'd like to see if anyone can offer a solution. I have a request to run some 16mm at our location. I have worked out the focal length for the lens required which is 1.5". No problem there, but I don't have that focal length available and I'm in no position so blow $200-300 on one. I have a stack of 35mm lenses handy and I need to know what (35mm) focal length I could use to get an identical image size through a (16mm) 1.5" lens. Just to clarify, I want to run 16mm films with a 35mm lens which is a 1.5" 16mm equivalent. Would any one know how I can calculate this? Cheers  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 05-21-2012 07:00 PM                        1.5" The focal length is a property of the lens, not the film format.  |  IP: Logged Ian Parfrey Phenomenal Film Handler Posts: 1049 From: Imbil Australia 26 deg 27' 42.66" S 152 deg 42' 23.40" E Registered: Feb 2009 posted 05-21-2012 11:20 PM                     Thanks for the info Scott. As that mean a 1.5" 16mm lens and a 1.5" 35mm lens would both give the same screen width using the standard 16mm aperture width of 0.380" through each lens, then it is perfectly feasible to use a 35mm lens with the only issues remaining being barrel diameter and back focus.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 05-24-2012 12:35 AM                     When comparing 16mm to 35mm, I've used the 2/1 ratio of sizing. A common lens for 16mm lenses have been the 2inch variety, where in 35mm terms that would almost be a 4inch lens to project the same size image close to the same throw distance since the frame size of 16mm to 35mm is almost double in size (give or take a few feet on the throw since the frame size isn't exactly a 2/1 size comparison), but it's close. 16MM = .404 x.295 (1.369:1 aperture) 35MM = .838 x.700 (cinemascope aperture) .825 x .600 (academy 1.37:1 aperture) You can see that the difference between 16mm and 35mm with academy aperture are almost double in size. Thus, a 3inch, 35mm lens would be close to the 1.5inches that your 16mm setup uses, would be needed.  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 05-24-2012 01:37 AM                        Monte -- interesting method. I just went through this for a venue that will use 130mm lenses for 1.37:1 Academy. If they ever run 16mm, they will need a 62mm lens (which they don't actually make, but whatever...60mm could be made to work if the masking is brought in on all sides). Which is fairly close to the 65mm that your method would predict. In most theatres, 38mm (1.5") is in the ballpark for 16mm, or at least close enough to get away with. I never understood why most 16mm classroom projectors come with a 2" lens. In most classrooms and other venues, the resulting picture is just way too small. A 1.5" lens would have been a much more reasonable standard. edit: re-did math and corrected focal length [ 05-24-2012, 07:12 PM: Message edited by: Scott Norwood ]  |  IP: Logged Rick Raskin Phenomenal Film Handler Posts: 1100 From: Manassas Virginia Registered: Jan 2003 posted 05-24-2012 05:21 AM                     How does one mount a 35mm projector lens on a 16mm projector?  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 05-24-2012 08:04 AM                     How about using the ratio between the hypotenuse of the picture area to determine the scale factor of the lens? 16mm: SQRT(0.404^2 + 0.295^2) = 0.50024... 35mm: SQRT(0.825^2 + 0.600^2) = 1.02011... 0.50 ÷ 1.02 = 0.49 -OR- 1.02 ÷ .50 = 2.04 Thus, when changing from 35mm to 16mm you multiply by 0.49. When changing from 16mm to 35mm you multiply by 2.04. Or, if you only want to remember one number, multiply by 2.04 when going to a larger film but divide by 2.04 when going to the smaller. Yes, you could use 0.49 but I think it's easier to do the math in your head if you use 2.04. The rationale for this comes from photography. When deciding on a lens for a camera with a given film format, one often uses the hypotenuse of the film frame as a starting point. (i.e. Determining the size of the "normal" lens for a given film format.) As we know, a projector is basically a "reverse" camera. Right? Therefore, the method of choosing a lens for a given format of movie film should hold true. No? Therefore, I would say calculations show that Monte's method makes sense. Scale the lens, up or down, by a factor of 2 or, if you want to be exact, use 2.04. Or, if you want to be hair-splitting exact, calculate the ratio of the hypotenuses. quote: Rick Raskin How does one mount a 35mm projector lens on a 16mm projector?  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-24-2012 09:11 AM                     If you calculate that you need 1.5" lens it makes no difference if it was designed for 16 35 or 70mm film now if you went the other difection and tried to use a lens from a 16mm machine with 70mm film the lens would not be able to accept the image size and would vignette The only big issue maybe getting the physically larger diameter of the 35mm lens close enough to the film plane because of mechanical restrictions to focus  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 05-24-2012 10:29 AM                        Thank you, Gordon. I think they are over thinking this! Louis  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 05-24-2012 11:58 AM                        The Kinoton FP-38E uses the same lens mount for both 35mm and 16mm, and 35mm lenses are used on it as a matter of course. Otherwise, there seems to be little standardization in 16mm lenses. The Prevost takes a slightly larger barrel diameter than the B&H 500-series. The Eiki lens barrel is slightly smaller than the B&H, and the Elmo lens barrel is even smaller, with a different focus mechanism. If I remember correctly, the Hortson takes the same lenses as the Prevost, but don't quote me on that.  |  IP: Logged Monte L Fullmer Film God Posts: 8367 From: Nampa, Idaho, USA Registered: Nov 2004 posted 05-24-2012 03:20 PM                     quote: Scott Norwood I never understood why most 16mm classroom projectors come with a 2" lens. In most classrooms and other venues, the resulting picture is just way too small. A 1.5" lens would have been a much more reasonable standard. I would call it two things, but I'm sure that more factors play into this: 1- The size of classroom-being the length and with the machine in the back of the room-and the size of their pulldown, or tripod screens that were had. ....or... 2- With the size of the frame on this smaller gauge, the light output would have to be increased being most 16mm units carried only 750 to 1kW bulbs (and newer units used 250w halogens) in them to give a decent presentation.  |  IP: Logged Jeff Taylor Jedi Master Film Handler Posts: 601 From: Chatham, NJ/East Hampton, NY Registered: Apr 2000 posted 05-24-2012 03:37 PM                     It's too bad you say you need a 1.5" or 38mm lens. I don't know what projector/barrel size you're using, but longer lenses are a dime a dozen on ebay. It's only the short (i.e. less than 2"/50mm) lenses that carry a premium. Still, I got a 1" standard barrel recently for $29 (vs I don't care to say what I paid for a 30mm Schneider for Eiki xenon!).  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 05-24-2012 03:48 PM                     Hortson and FP16 Eiki Fumeo use a 42.5mm diameter The Prevost/Zeis Favorite are 62mm Which i believe is the B&H lens  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-24-2012 04:13 PM                     And the 16mm projectable image size is .286 x .380  |  IP: Logged Jeff Taylor Jedi Master Film Handler Posts: 601 From: Chatham, NJ/East Hampton, NY Registered: Apr 2000 posted 05-24-2012 04:30 PM                     B&H models 5xx-25xx use 52.5mm barrel lenses, as do Eastman 25, 275, and JAN's. Eiki and Hokushin are 42.5mm, as are B&H 35xx machines which are re-badged Eiki's. The old standard lenses used in RCA (except 1600), DeVry, Ampro, Movie Mite, Natco, Victor, etc, etc, are 1-5/8". I'm not dead sure on Elmo (slightly larger than the Eiki's), or the 1xx-3xx Bell&Howell (slightly smaller than the old standard variety as are Pageants).  |  IP: Logged

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