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Author Topic: How steady is your projector? Quantitatively. John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 05-17-2008 12:58 AM                     Over in Best/worst projector, I asked people to justify their claims of projector steadiness with some quantitative numbers. No one bit So, on a pair of Century Cs, which couldn't possibly be all that great, here are some measurements of steadiness. I'm reminded that John Pytlak encouraged measuring steadiness not-from-a-loop, so here are some numbers for vertical steadiness from looking at perfs with the aperture pulled. With this particular lens, the projected height of a perf was 19.75" -- a KS1870 perf is actually 0.078". Projector #1: 5/16" * (078 mils/19.75") => 0.00123" Projector #2: 7/16" * (078 mils/19.75") => 0.00173" Or, in RP40 squares: Projector #1: 0.00123/0.004125 => 0.299 squares Projector #2: 0.00173/0.004125 => 0.419 squares Turns out that's pretty bad. In this 1999 post, John Pytlak described the measurement standard used by Kodak's Screencheck: quote: Steadiness is measured using a roll of SMPTE 35-PA (RP40) test film. For vertical steadiness (jump), an "A" rating is less than 1/10 of a square movement, a "B" is 1/10 square, a "C" is 2/10, a "D" is 3/10 and an "F" is greater than 3/10. For horizontal movement (weave), "A" is less than 4/10 of a square movement, "B" is 4/10, "C" is 5/10, "D" is 6/10, and "F" is more than 6/10. These criteria are based on SMPTE Recommended Practice RP105, "Method of Determining the Degree of Jump and Weave...". As you know, each square on the 35-PA film represents 1/2 percent of image width, or 0.004125 inches on the film. By that standard, my Projector #1 grades out at a D, and my #2 at an F. Pretty bad! Admittedly I think the gate tension was probably set waaay low, so I should probably reset it and rerun the test. But in the meantime, post your numbers! --jhawk  |  IP: Logged John Walsh Film God Posts: 2490 From: Connecticut, USA, Earth, Milky Way Registered: Oct 1999 posted 05-17-2008 10:48 AM                     Funny, I was just explaining to a friend about my doing the same test on some projectors 1982. I've tossed most of the notes but the one that remains lists of a pair of rebuilt JJ's, and one SA. I was using RP105-1981 (don't know if a newer practise has been published or, if so, if it's any different.) We couldn't get a long length of 35PA; (too expensive) we had to use 8ft loops. The JJ's did OK at class 'B' (0.18%). The one SA at our 'dump' theater was a class 'D' (0.31%). Those are jump numbers; for some reason I didn't do weave. Not that it matters; none of those projectors are in service anymore. Also, few intermittent rebuilders are going to take an intermittent back and redo it.  |  IP: Logged Sean McKinnon Phenomenal Film Handler Posts: 1712 From: Peabody Massachusetts Registered: Sep 2000 posted 05-17-2008 03:02 PM                        unfortunately, I no longer work for the company I used to work for where I serviced the projectors we were discussing.  |  IP: Logged Galen Murphy-Fahlgren Master Film Handler Posts: 405 From: Canton, MI, USA Registered: Oct 2007 posted 05-18-2008 06:01 PM                     As I said, today was my first opportunity to do any sort of check on this front, and even today I only had time enough to eyeball it from booth, and only a couple of my projectors. All measures were made in scope. Here we go: Aud. 7- Proj. V5 Horizontal movement was almost a full square. Vertical, about .5. F Aud. 1 Proj. V5 Horizontal, approx. .75, vertical about .5 again. F Aud. 4 Proj. Simplex XL Horizontal around .3 or .4. I could detect no vertical movement, steady as a rock. B? Aud. 5 Proj. XL Horizontal .7 or so, vertical .4. F. Again, these were eyeballed, and I'm lucky to have had time to do even that today. I will attempt to get some more accurate figures and figures for my other V5 and my pair of Christies. Also, I probably need a new RP40, I almost think mine is acetate. While that would obviously affect overall values because of gate tension being set for poly, could it have an effect on relative values, ie, some designs being better suited to accommodating different base thickness? What steps can I take to improve the steadiness of these projectors? I mean, it isn't like I want the V5 to fail. I'm trying to provide good presentation, as I think most people are. I'm just doing it with very little experience and minimal guidance.  |  IP: Logged Sean McKinnon Phenomenal Film Handler Posts: 1712 From: Peabody Massachusetts Registered: Sep 2000 posted 05-19-2008 09:58 AM                        I went through my files and pulled out my technician copies of my old service reports and PM reports. It seems like I recorded everything else except these measurements, I just noted either no or minimal horizontal movement (weave), or no or minimal vertical movement (jitter). Sorry, I tend to be pretty thorough but I guess not that thorough.  |  IP: Logged Richard P. May Expert Film Handler Posts: 243 From: Los Angeles, CA Registered: Jan 2006 posted 05-19-2008 12:39 PM                     This is a good exercise. On our Norelco FP20s: Proj 1 - C Proj 2 - A RPM  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 05-19-2008 01:01 PM                     Real numbers, Richard? I'll try to do ours more properly... --jhawk  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 05-19-2008 10:27 PM                     Today I looked at a Kinoton FP30E running 35PA...which is not always the most steady of test films...it varies batch-to-batch... 1/20th of a square jump (could have been closer to 1/30th...the screen was up there though I was trying to measure at the screen). So I guess that puts it in an "A" classification.  |  IP: Logged Michael Moore Expert Film Handler Posts: 188 From: Dover, DE / USA Registered: Jun 2006 posted 05-21-2008 08:15 AM                        If i did this test with a screen say 10 feet away from the projector, (in our place I have room in the balcony to set up a smaller screen) will the test results be comparable to our 90 foot throw?  |  IP: Logged Paul Mayer Oh get out of it Melvin, before it pulls you under! Posts: 3836 From: Albuquerque, NM Registered: Feb 2000 posted 05-21-2008 12:02 PM                        Since you're going to be measuring how much a given projected square moves in relation to its own height and width, the actual size of the square is not important. However, on such a small screen it may become difficult to precisely measure how much the square moves since it will be quite small.  |  IP: Logged Richard P. May Expert Film Handler Posts: 243 From: Los Angeles, CA Registered: Jan 2006 posted 05-21-2008 02:15 PM                     This is a lab screening room, with about a 6 ft. high screen. An exact measurement is pretty hard to accomplish. I re-viewed with a new, Estar based projection chart, originally created by the MGM Camera Dept. It's somewhat different from SMPTE, but with the necessary objects to compare the image with the screen edge or masking. With this, there is absolutely no discernable movement with either of our FP40s. RPM  |  IP: Logged Carey Barber Expert Film Handler Posts: 143 From: Newport News, VA, USA Registered: Jan 2003 posted 05-22-2008 11:57 AM                     What is the recommended length for a good test loop of 35PA?  |  IP: Logged Paul Mayer Oh get out of it Melvin, before it pulls you under! Posts: 3836 From: Albuquerque, NM Registered: Feb 2000 posted 05-22-2008 01:30 PM                        For this kind of test a loop is not recommended, since a loop doesn't recreate the typical condition of film running through a projector. With each pass the loop heats up a bit more and changes the way the film behaves when it is stopped and flashed within the gate. Loops are fine for doing things like checking and filing plates, but not for critical testing. If you absolutely must use a loop, longer is better. Mine all happen to be 8-footers.  |  IP: Logged Carey Barber Expert Film Handler Posts: 143 From: Newport News, VA, USA Registered: Jan 2003 posted 05-22-2008 09:10 PM                     Okay...This may be a stupid question, but what do you use in place of a loop? Are you just using tons of 35PA and running it through? I would think that you would want a few minutes worth to give you time to check everything. That would be awfully expensive, as that test film is not cheap.  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 05-22-2008 09:18 PM                     I did my numbers from looking at perfs without the aperture plate. If you run a reel of 35PA, you get much less wear than you do with a loop. It might not be economically reasonable for you, but it is the better way (We do use a 50' length of Cat69T for our Dolby Alignments, with heads and tails. That works pretty well, and lasts a long time...) --jhawk  |  IP: Logged

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