Film-Tech Forum ARCHIVE: Slow Projector

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Posted by William Phillips (Member # 1162) on 07-23-2006, 03:03 PM:

One of my projectors runs a bit slow, a film that runs 2hours 30 on another machine will run 2hours 34mins approx on the slow one.
I have got an inverter on the machine so can speed it up. How much in frames per second should I increase it??
Projector is a Cinemeccanica 5B-4000

Posted by Louis Bornwasser (Member # 3063) on 07-23-2006, 03:18 PM:

You will need a stopwatch and exactly 45 ft of junk film. Adjust speed to have the splice occur every 30 seconds. Allow to run for several minutes.

Method #2: 1000 hz sound loop and frequency counter.

Method #3: use a strobe with digital readout: set for 1440 flashs per minute. Speed of shutter is 1440 rpm. Louis

Posted by Darryl Spicer (Member # 711) on 07-23-2006, 03:22 PM:

1 frame per second increase will probably do the trick. Sounds like it may be running close to 23 frames instead of 24 frames per second.

Posted by William Phillips (Member # 1162) on 07-23-2006, 03:48 PM:

Cheers guys,
Its been bugging me for ages. I could never decide if one was fast or the other slow. The slow machine has got a 2 blade shutter and there is a bit of flicker on screen, its just visable. The other machine has a 3 blade, so no flicker at all. It got to the point where i swapped the shutters over to see if 2 blade still flickered on other machine and no. So thats how i came to the conclusion that my machine is slow. And now thinking about it I am going to build a sprocket hole counter as of course it sould be 96HZ [Roll Eyes]

While im at it should make a milage counter to see how much they do a year [Big Grin]

Posted by John Anastasio (Member # 607) on 07-24-2006, 07:04 PM:

Or you could figure it in furlongs per fortnight!

Posted by Marc Hansen (Member # 705) on 07-24-2006, 10:11 PM:

John-
I had a physics prof in college (Strieb I think, it was 30 years ago) that used furlongs per fortnight at every chance he could. I've never gotten it out of my mind. You didn't take classes from him did you? I almost never hear it used.
Marc

Posted by Louis Bornwasser (Member # 3063) on 07-24-2006, 11:59 PM:

We had that in high school back in 1964 in Louisville KY. Louis

Posted by Sam D. Chavez (Member # 1841) on 07-25-2006, 09:09 AM:

I use 6, 9 or 10 foot loops, exactly down to the perf, and then run the film, count the splice clicks thru the gate for 30 seconds or a minute and then do the math in my head. 10 Feet = 9 clicks per minute, etc.

Posted by Steve Guttag (Member # 268) on 07-25-2006, 10:25 AM:

I much prefer the strobe route...not only will it tell you speed pretty darn fast without the math...it also is useful to check on other problems in the drive train.

Steve

Posted by Frank Angel (Member # 248) on 07-31-2006, 11:09 AM:

Wasn't there a file posted somewhere here on FT that you could print out which contained an image of a round strobe wheel that you could stick to one of the sprocket drives to read speed? Or am I dreaming?

Posted by John Pytlak (Member # 331) on 07-31-2006, 12:46 PM:

quote: Frank Angel
Wasn't there a file posted somewhere here on FT that you could print out which contained an image of a round strobe wheel that you could stick to one of the sprocket drives to read speed? Or am I dreaming?

You're thinking of the segmented disks that were used to checking the speed of record turntables, where a simple 60Hz neon "strobe" was used to illuminate the disk. But a projector shutter shaft is likely too fast (1440rpm) for that technique to be accurate.

Posted by Ron Yost (Member # 1850) on 07-31-2006, 01:18 PM:

Frank, Yes there was a pic of a strobe dial posted .. I have it, but can't remember who made it. It's called 'dial.jpg'. Do you want it? If I could remember my password [Eek!]

I'd upload it again. I pasted it on a sound sprocket in my 9030, just for grins. Seems to work fine, tho my machine is running just a tad slow according to the 'dial'.

Ron Yost

Posted by John Pytlak (Member # 331) on 07-31-2006, 02:23 PM:

Thanks. The shutter shaft may be too fast for a disk method (1440 rpm), but a 16-tooth feed or holdback sprocket rotating at 360 rpm might be within range when illuminated by a simple 60 Hz strobe.

Posted by Mark Gulbrandsen (Member # 72) on 07-31-2006, 07:10 PM:

quote: Steve Guttag
I much prefer the strobe route...not only will it tell you speed pretty darn fast without the math...it also is useful to check on other problems in the drive train.

I have a General radio Strobe thats crystal refrenced which I've had for many years. I actually use quite frequently. I originally bought it for checking for film flutter in my 8 perf projctor and speed accuracy on my 8 perf camera. Recently it helped us big time on solving a Simplex 1060 scratching problem. you couldn't see it scratch film with the naked eye but the problem was very easy to see happening with the strobe. I would also rececomend the use of a direct reading digital tach. on the shutter shaft. These are fairly inexpensive if you search them out... but not useful for finding scratching problems.

If worse comes to worse you can only allow slow audiences in that house.

Mark

Posted by David Favel (Member # 1125) on 08-01-2006, 06:01 PM:

I have inverters with the paramaters able to be observed and changed on a detachable faceplate.
All I had to do was change from 49 to 50 Hertz

Posted by Tim Reed (Member # 137) on 08-04-2006, 02:44 AM:

quote: Ron Yost
there was a pic of a strobe dial posted .. I have it, but can't remember who made it.

That was me.

quote: John Pytlak
a projector shutter shaft is likely too fast (1440rpm) for that technique to be accurate.

The traditional method is to stick them on a sprocket, as Frank mentioned.

Posted by Michael Schaffer (Member # 1204) on 08-04-2006, 04:33 AM:

quote: Mark Gulbrandsen
Recently it helped us big time on solving a Simplex 1060 scratching problem. you couldn't see it scratch film with the naked eye but the problem was very easy to see happening with the strobe.

How did that help you find the place where the scratching occurred? [Confused]

Posted by Ron Yost (Member # 1850) on 08-04-2006, 12:04 PM:

Thanks, Tim! It did later pop into my foggy ole' brain that it may have been you. [Smile]

Ron Yost

Posted by Richard Fowler (Member # 893) on 08-04-2006, 12:37 PM:

Using a strobe helps freeze an image when used in situations such as surface or base scratches.....have used this on cameras and optical printers. In addition to strobes, I use an LED display box, when viewed through shutter, checks for speed and forward or backward drift.

Posted by Sean McKinnon (Member # 612) on 08-05-2006, 02:02 PM:

If you change the speed in which the projector runs wouldnt you also have to readjust the analog sound optics and or slit loss eq?

Posted by Michael Schaffer (Member # 1204) on 08-05-2006, 03:14 PM:

No. Slitloss EQ is for focus, it has nothing to do with the speed. Theoretically, if you change the speed, the frequency response and therefore also the HF range change, but the slitloss adjustment is relative anyway, not absolute. One could argue that if the projecor is made slower, some of the highest frquencies would drop, but so do the frequencies in all other bands and the difference is so minimal you can't probably even see it on the analyzer. Plus it's again relative response=flatness of response, not an absolute HF target that is aimed for.

quote: Richard Fowler
Using a strobe helps freeze an image when used in situations such as surface or base scratches.

How? Sorry to be so slowbrained here, apparently it is something very obvious that I am overlooking, but I don't quite understand the connection and application of the strobe disc here.

Posted by John Hawkinson (Member # 1135) on 08-05-2006, 03:43 PM:

Richard doesn't mean the disc, he means an actual strobe light, aka stroboscope.

--jhawk

Posted by Steve Guttag (Member # 268) on 08-05-2006, 05:33 PM:

Michael,

The reason a strobe helps is the same reason movies work at all...persistance of vision allows movies to work with our eyes....however this same persistance of vision will keep you from seeing things clearly like film touching where it shouldn't.

Lets say you have the film buckleing such that it periodically bellies forward and rubs its face on a gate part...but it happens for less than 1/24 of a second and only on pull down. Your eye will never catch it.

Now use a strobe...with a strobe you can effectively "slow down" the projector yet still maintain the exact same operating conditions...then you will see in slow motion what is happening to the film as it travels. Depending on how regular the incident occurs, you can even freeze the film while it is making contact.

While I have not used a strobe for this sort of investigative work, I can see how someone might. I personally prefer the red Marks A Lot approach...Run a loop of virgin film...locate the scratch in question on the film....fill in the scratches with the red marks-a-lot...run the film again (keep the orientation and framing the same)....look for the red dust trail...it will point you to the culprit just about every time.

Want to see how smooth your machine is...that is when a Strobe comes in handy...you'd be amazed at how jerky most shutters run (think about all of the gear lashes between the motor and the shutter, and all of the frictions and different flywheel effects or elasticity of the belts)...it all adds up in the shutter.

Just be very careful when working with a strobe...Objects ARE spinning faster than they appear!

Steve

[ 08-05-2006, 08:07 PM: Message edited by: Steve Guttag ]

Posted by Charles Greenlee (Member # 3856) on 08-05-2006, 11:43 PM:

That reminds me, one of our projectors has a slight hesitation in the intermittant about 1/2 way through it's pull down, when rotating the motor by hand. The others don't. The projector is louder, the normal purr is a bit more edgey, but not by much, and that can be mostly attributed to the style of gate. It's a strong, don't remember the model number but from early 80's. It uses and older style flat trap and gate, the kind with the spring loaded bars on the gate and a rigid trap, rather than the curved kind with the rigid gate, and thin bands in the trap. The gate seems to add the noise, the picture seems fine. It's been running fine. I think it just may be a worn intermittant that has a little play in it, probably should be replaced on next PM visit. I'm definatly going to alert the tech when he comes by, but do you think this is an urgent issue?