Film-Tech Forum ARCHIVE: Cinemeccanica Victoria 5 change run/shutter speed

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Posted by Tony Smith (Member # 7191) on 02-14-2015, 11:54 AM:

Hi
My colleauge wishs to run some film 35 mm shot at 20 frames per second, on a Cinemeccanica Victoria 5 with 3 phase motor, not sure if it's 4 or 8 pole.
Its run via a Mitsubushi invertor, single phase in 3 phase out (50hz) type A024.
Anybody any knowledge on this topic that could please help.
The way I though we could do it is to run the motor slower, by around 17%.
If this is possible, whats the best way to do this, to reduce the 50hz by 17% to 41.5 Hz or reduce the 3 phase voltage, or none of these.

Tony Smith

Posted by Leo Enticknap (Member # 534) on 02-14-2015, 12:03 PM:

Reduce the frequency, using an inverter that allows you to change the output AC frequency, or replace the motor with a single phase one and adjust the voltage.

Below around 21-22fps you'll need a three-blade shutter or else the flicker will look bad. Cinemeccanica made one for the Vic 5: might be worth asking Sound Associates (the UK's official Cinemeccanica reseller) or Future Projections (a company that refurbishes film projectors of all makes) if they have one for sale. Otherwise, it's a case of keeping an eye on Ebay. Fitting and timing it is usually pretty easy, but depends on what sort of lamphouse is behind the projector and how it's mounted.

Posted by Tony Smith (Member # 7191) on 02-14-2015, 03:28 PM:

Hi Leo
Thank you

Tony Smith

Posted by Monte L Fullmer (Member # 2797) on 02-16-2015, 04:34 AM:

You can get away with a two wing shutter at 20FPS since that's 40hz in term of light pulses, but that's hitting the bottom threshold of a smooth image.

I ran a silent film on an XL with variable motor speed where we dropped the shutter speed down to 20FPS and the image on the screen was still good with minimal flicker-even though a three wing would have easily made for a nicer image.

-Monte

Posted by John Eickhof (Member # 323) on 02-16-2015, 10:56 AM:

A simple way to do it is to calculate the proper motor drive pulley for a 1/6th reduction in rpm that will put you at 20fps since the vic5 uses standard gilmer type drive belts this would be the easiest and least expensive way to do it. I would guess that the drive pulley would be one tooth or so less than stock and thus the same belt would be used with enough adjustment to take up the slack.

Posted by Tony Smith (Member # 7191) on 02-16-2015, 11:24 AM:

Hi Folks
Thanks for your help, this is a very interesting topic
to me, we are going to give the option of reducing motor
run speed to 20frames, and see how good the image is.

Tony Smith

Posted by Leo Enticknap (Member # 534) on 02-17-2015, 11:09 AM:

Hmm ... hadn't thought of using a smaller pulley on the motor shaft, but if you can get hold of one, fitting it would be very easy, and as John points out, the belt tensioner should be able to take up the extra.

As for shutters, correct me if I'm wrong, but I believe that there were at least two models of two-blade shutter made for the Vic 5 (perhaps one of them by an aftermarket supplier - not sure). The standard one was pretty easy to time and had larger blades than the "small blade" one, which was intended for situations where your lamp was essentially underpowered and you needed to squeeze every last lumen out of it. Timing the "small blade" one was absolutely critical and very difficult to prevent ghosting, but I'm guessing that it probably would be a little more flicker tolerant of sub-24 frame rates.

If you're showing full-gate silent prints using a Vic 5 installation regularly, then permanently installed three-blade shutters, lamps big enough to give you 16ft-l on a white light even with three-blade shutters installed and motors that can be adjusted between 16-25fps (25 to run the odd shot for PAL TV production, 35mm prints of which crop up in European arthouse cinemas from time to time) at the twist of a knob is an investment worth making.

You will also, of course, need lenses and plates for the full-gate silent ratio, though a workaround for that is to use the 'scope prime lens without the anamorph, which will also do for the silent and Movietone ratios (perfectly, if your masking can move at the top and/or bottom, and good enough for most people if your masking is sides only). The height of the frame in all three ratios (silent, Movietone and 2.39 'scope) is very close to identical. At the one place I worked which used Vic 5s for silent shows, we had the anamorphs on a bracket which swung out of the way to enable the 'scope primes to be used for silent and Movietone.