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Author Topic: Would a Contemporary Lens Have a Greater Depth of Field? Bill Enos Film God Posts: 2081 From: Richmond, Virginia, USA Registered: Apr 2000 posted 04-07-2007 07:38 PM                     Every year this is an issue on a couple of festivals that have subtitles. On scope if subtitles are sharp the center of the screen and up are soft. Flat is not an issue, there seems to be enough depth of field for both to be OK, never got a complaint. Here is the info. Throw 110 ft., angle 14 degrees, screen height 16.5+- feet same for flat and scope, width scope 36'4", width flat 26'. Lenses---some history here, no laughing please. Scope prime Kollmorgen BX 163 5.5" with anamorphic B&L Cinemascope I. Flat Kollmorgen BX 241 3.75". The screen is not angled. Flat gives sharp subs and image, scope is noticeably soft if subs are sharp. Would modern lenses improve on this depth of field problem on scope? Seems to me that the issue lies in the anamorphic since flat even with much greater magnification doesnt have this problem.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 04-07-2007 08:16 PM                        Probably the projector is OK since flat is OK. (It is possible for this to be wrong since you are using the full height of the film only in scope.) The only thing I see wrong on scope is that the BX-163 (I think) has a primitive magnecom built in; not the greatest idea. I would get a modern scope backup and test to see if a full or partial cure happened. Louis  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-07-2007 08:53 PM                     There are many factors in play here. The lenses you are using are notorious for poor focus uniformity due to the presumption that the film was flat in the gate. However, when heat hits the film, it swells towards the light source making the focus want to be at the screen plane and further away at the edges. 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. Now, combine that with your steep down angle and you have yourself a risky situation. Note, for flat, you have less heat hitting the film (more hitting the aperture plate) so it will suffer less in this regard. The Scope attachment should perform zero magnification in the vertical plane (Cylindrical lens elements, not spherical). However, it is possible for the elements to rotate with respect to themselves that will prevent one from EVER getting uniform focus. I would think that modern lenses could have a rather marked improvement to what you have now (both prime and anamorphic attachment). The ISCO Blue Star is real hard to beat for anamorphic attachments. As for prime lenses, you are looking at a 140mm...they normally do pretty darn well with off axis projection. Either ISCO or Schneider will do you real good. If you have light to spare, Schneider can make stop down rings for their lenses greater than 100mm. These stop down rings will also improve corner-corner sharpness. One thing you can check though it won't be conclusive is to pull the anamorphic and look at real target film and note the resolution...then see what the resolution with the anamorphic attachment on. Louis is mistaken about the model you listed as having a crude MagnaCom in it...those were the short EF lenses. The BX294 is the lens series that had the Magnacom 69 in them...they also had an "X" in their name. Another thing going for new lenses is that you ran carbons for many years and no doubt had smokers in the booth...I've seen many a lens collect soot from all that. If you have straight gates in your XLs...you might also find that curved gates improve your focus situation. So...change the prime lenses and you will see a marked improvement...change them both and you won't be able to believe how much better it can be.  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 04-07-2007 10:34 PM                     Lenses are a definite, but in situations where I have a top/bottom or left/right focus issue, it can almost always be corrected with some careful turret or gate adjustments, or sometimes shimming of the lenses in their holders. I've got a nice condition used ISCO 135mm lens and anamorphic I can loan you for testing purposes if you pay the freight.  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 04-08-2007 06:40 AM                        I think Steve covered it all very well! Louis  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 04-08-2007 09:51 AM                     A minor point ... If the films have subtitles burned in with a laser, they will be a little out of the focal plane of the emulsion, causing a bit more of a focus problem. But, yeah, a 14 deg tilt is gonna cause some issues.  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 04-08-2007 02:38 PM                     We have had the same issues with scope in our theater. We upgraded 3 out of 4 lenses to schneiders with schneider anamorphics. What a difference.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 04-08-2007 04:03 PM                     I have found out that using one complete lens for cinemascope gives sharper and better focus in subtitled features throughout the image rather than using a 2 lens solution (lens and anamorphic) When using 2 lens solution the projector has to be 0 degrees throw to the screen in order to have a uniform sharp image. Laser subtitles are the main cause of problem. When using "wax" subtitles you should not have any problem. Demetris  |  IP: Logged Richard May Phenomenal Film Handler Posts: 1057 From: Floral Park, NY USA Registered: Aug 2004 posted 04-08-2007 04:11 PM                     I tried getting an intergrated anamorphic but Schneider didn't make one for the focal length I needed. As for our theater, luckily we are at a zero angle.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 04-08-2007 05:26 PM                     A one piece really is actually two seperate lenses and many integrated anamorphics backup lens can be unscrewed from the anamorph. If you think two part lenses are bad you obviously have not tried a Blue Star anamorphic with one of the higher quality Isco backups. The difference is beyond astonishing! Mark  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 04-08-2007 08:34 PM                     Demetris...what you said makes ZERO sense. There is nothing inherently better with integrated anamorphics...in fact, they are the inferior ones. In the name of size and space, they are almost all 4-element designs that are inferior to the Isco 5-element, 6-element designs. Schneider's "integrated" anamorphic may be ordered as a separate piece as the "ES Anamorphic". As short anamorphics go, it is the best I've found. Once you get to 55-60mm though, the Blue-Star anamorphic attachment is notably superior to others. I've used them with all sorts of down angles as well as lens shifting. One thing many people don't seem to realize is that focus starts with the lamp itself and how it is aligned as well as reflector design. They all work as a team.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 04-09-2007 07:24 AM                     I have this theater with extreme angle throw and we can not get even focus on scope films (talking about huge angle) no matter how hard we try. Combination of Galileo 105mm lens with Isco Optic Gold Anamorphic. This is mostly to the throw angle rather than the lenses. I do though have the same setup in a village cinema with the same result and very little throw angle. A small country can keep a stock of lenses just to check whether a problem can be fixed but in the second case, when I tried a single lens solution from Isco Optics which I borrowed from another cinema and then gave back, I managed to achieve perfectly sharp focus in all films including films with laser subtitles. Demetris  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 04-09-2007 08:13 AM                     With extreme down angles sometimes the screen has to be tipped back at the top to solve both keystone and focus issues. There were several theaters in Chicago like that. I forgot to mention that the down tilt was so extreme in these theaters that the xenon lamps had to be installed in the reverse fashion as in a Super Trooper spotlight. This way they'd stay lit and just make warranty hours. Mark Mark [ 04-09-2007, 09:44 AM: Message edited by: Mark Gulbrandsen ]  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 04-09-2007 11:25 AM                        'scuse me if this sounds impractical, but could the trap/gate be angled somehow? It might not address keystoning, but wouldn't it fix the focus error?  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 04-09-2007 11:57 AM                       People were shimming Century gate shoes 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. [ 04-09-2007, 06:42 PM: Message edited by: Sam D. Chavez ]  |  IP: Logged

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