Film-Tech Forum ARCHIVE: Cinemeccanica Victoria 5 film run speed

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Posted by Tony Smith (Member # 7191) on 02-27-2015, 10:50 AM:

Hi Folks
Very much a newbie to this world, very interesting it is too.
After a little advice, and help Please.
I have after my first thread manaaged to run a Cinemeccanica Victoria 5, at slower run speed, by changing the motor high speed frequency setting in it's Mitsubushi single to three phase invertor.
My question is, what is the best method of checking its new run speed, we are going to try and run 20 frames per second achive film (protection copy )
I have built from a kit, a LED twin bright leds, stroboscope, which its max flashing speed is 20 hz.
I have tried looking at the shutter running and strobing (at the rear end where the spindel comes out)
Is there a better way to do this and get a stationary image when the strobe is in sync?

Tony Smith

Posted by Sam D. Chavez (Member # 1841) on 02-27-2015, 11:43 AM:

An easy way is to cut a loop some multiple of 20 FPS. Say 100 frames long exactly. Run the loop and count the clicks as they go thru the gate and it should go thru 10 times exactly in one minute. Repeat as needed after tweaking the speed control.

Helps to have a footage counter to make a perfect loop.

Posted by Leo Enticknap (Member # 534) on 02-27-2015, 01:33 PM:

If your motor runs at 24fps at normal mains frequency (50Hz in the UK), then you can work it out using simple maths.

20 is 5/6 of 24.

50 / 6 = 8 and one third

Therefore, set your inverter to 41.66Hz (or as near to that as you can get it), and you should be running at 20fps.

Posted by Sam D. Chavez (Member # 1841) on 02-27-2015, 03:46 PM:

Should is the operative word. I'm just doing some of these and there can be a little loss or slippage.

A tach that reads the output of a shaft encoder or the loop method I described are closer to proof over a period of time.

Posted by Tony Smith (Member # 7191) on 02-27-2015, 04:31 PM:

Hi Folks
Thank you for your answers
I have changed the frequency from 50 hz to 41 hz, the projector at 41 hz is running slower,just trying to get my head around who to measure the actual speed now.
Thanks again folks will try your tips out

Tony Smith

Posted by Louis Bornwasser (Member # 3063) on 02-27-2015, 08:20 PM:

As a guy who always thinks in audio terms:

Use a 1000 Hz loop and a frequency counter. For 24 frames=1000 Hz.

Do the math for other speeds. (Works upward for 30 frames as well.)

Posted by Sam D. Chavez (Member # 1841) on 02-27-2015, 09:20 PM:

Oy, Louis,

Where is one to find 1K loops at this late date? And it was never that accurate in the first place. Dolby Tone is all over the place freq wise and is certainly not 1K in any case.

Other than that, great idea!

Posted by Louis Bornwasser (Member # 3063) on 02-28-2015, 03:41 PM:

I still have lots of 1k. Yes, I counted it and it looks to be off by about 1 Hz. Made back in the day when tight parameters were specified by John Moseley, even though they didn't affect anything we were testing??

Carl Greenberg used this technique to get 30 fps for Oklahoma in 70mm. (Threaded 35mm optical at the same time as 70mm film was playing ) 1250 Hz=30 fps.

Yah, I know!

Posted by Tony Smith (Member # 7191) on 02-28-2015, 05:10 PM:

Hi Folks
Thanks again for your answers, just one quick question, if I could.
The Cinemeccanica Victoria 5 has a two blade shutter, so as the film rate in 50 hz is 24 frames per second,so I would expect the shutter rate to be the same, so it lets the light through when the film is stationary in the gate, so with a twin blade shutter is the actual run speed 12 frames per second,or is the speed 24fps and the film same frame shown light twice.
I know this is a basic question to you guys but as a newbie, still trying to work thse things out
Tony Smith

Posted by Stephan Shelley (Member # 8587) on 02-28-2015, 05:18 PM:

It actually flashes the same frame twice to reduce flicker. 48 flashes per second.

Posted by Sam D. Chavez (Member # 1841) on 02-28-2015, 08:34 PM:

I measured SMPTE 1K tone 20 years ago last time and it was more than 3% off 1,000 Hz. Sir John Mosely must have been drinking that week! Of course 1K was made by more than one entity and the absolute freq, was never considered critical, it was just for a relative level. The level recorded on the film also varied from year to year or whenever a new negative needed to be recorded.

Hollywood test films were pretty sloppy back in the day.

I can hear Steve's shoes approaching or reproaching so I better sign off.
Lot's of ways to measure film speed but the whole point is to get it dead on seeing as there is now a way to do it. All we could do is complain about it before variable frequency drives.

Posted by Gordon McLeod (Member # 33) on 03-01-2015, 07:27 AM:

Put a solar cell in front of the lens and use a frequency counter on the flashing of the shutter

Posted by Tony Smith (Member # 7191) on 03-01-2015, 07:42 AM:

Ji Folks
Thanks again for your replies, have learn't a lot from your forum
and the memebers on it.

I think what I will try first is using a stroboscope, put a mark
on the spindle with the dual blade shutter on, check it speed of rotation, looking for 48 rps in 24 frames, and note the change when running 20 frames, looking for 40 rps,or as near as possible.

All this due to the cinema being booked for a film showing conference, where a fair amount of archive film shot around 20frames is to be run, a request was put in for us to blow the dust off the 35 mm Cinemeccanica Victoria 5, and show the film as it was intended. thats not off a DVD.
Tony Smith

Posted by Dave Macaulay (Member # 813) on 03-01-2015, 08:20 AM:

I would go with Sam's loop method. No fuss, no guessing, and as accurate as your stopwatch (unless you can't count frames in the loop or passes).
There are many frequency meter apps for iThings® if you want to try more complicated solutions.

Posted by Leo Enticknap (Member # 534) on 03-01-2015, 03:36 PM:

By all means go for complete accuracy if it's important (or if people are breathing down your neck), but as an aside, the people who shot the movies you're going to show probably didn't.

If you're being told 20fps I'm guessing that you're showing British and/or French movies from the mid to late 1920s. Most of the Hollywood studios were shooting at 24 (and specifying projection at 24) from the early '20s onwards. Germany and the Soviets mostly stuck at 16-18 right up until the conversion to sound. 20 was typically used by British and French studios as a compromise between not driving up film stock costs too much, and using a fast enough frame rate that the emerging picture palaces (longer throws to bigger screens, hence the need for more light) could project a reasonably bright, low-flicker picture.

The point is that until the conversion to sound, most of these studios used hand-cranked cameras. If the operator was aiming for 20, the actual speed of each shot could be anywhere between 18-22, and could even vary within a shot. When Kevin Brownlow was doing his "Thames Silents" video versions in the 1980s and '90s, he would meticulously adjust the transfer speed of each shot to try to achieve a consistency of movement across the movie as a whole. They look great - "better" than original audiences would have seen, in fact. So in one respect, you really don't need to worry about getting the frame rate bang on, because that was neither achievable nor expected during the silent period. The need to sync the frame rate accurately and reliably between the camera and the projector only materialised with sound. Very few people can see a slight (as in, 2-3 frames per second) speed difference in the image, but they'll very easily hear it on the audio: the same 2-3fps difference is enough to make a bass baritone sound like Mickey Mouse.

Posted by Sam D. Chavez (Member # 1841) on 03-01-2015, 07:00 PM:

Yes, what Leo says, but there's no point to having speed controls and preset speeds that are other than what they state.

Posted by Louis Bornwasser (Member # 3063) on 03-04-2015, 07:58 AM:

If you have a strobe, shutter shaft speed is 1440 at 24fps. My strobe has a digital read out so calculate what you need.

Posted by Tony Smith (Member # 7191) on 03-05-2015, 11:40 AM:

Hi Folks
Thanks for your help, we have just run a load of 1920's French archive film shot at 20 frame(we have protection copy) and the results are excellent. the aspect ratio is 1.33.1 but we put the closest gate insert in we had, and all the headroom is back,
we checked the shutter speed(two blade shutter) with a stroboscope we made from a kit, calibrated it using a
oscilloscope, looking at the LED switching, when we strobed out the shutter it was stationary at 40 hz , Misubushi invertor set to high run speed of 41hz from 50hz. Both the projector and the motor, run sounds good and run cool. Only one item thats not happy was the film break detector, not happy at lower run speeds, but this can be tweeked, otherwise have a engineer close by if film breaks...................

Posted by Monte L Fullmer (Member # 2797) on 03-05-2015, 03:45 PM:

Might have to take the wrap detector out of the loop if it doesn't like the slower film speed..

.. a jumper wire across the micro switch wire connections does wonders for bypassing.

Posted by Tony Smith (Member # 7191) on 03-05-2015, 04:07 PM:

Hi
Yes that will do,but just have it switch to off works ok, thanks for reply

Posted by Tom McGarrity (Member # 7320) on 04-06-2015, 05:11 PM:

Just buy a model aeroplane digital tacho for a few pounds.
It works a treat.