Bauer sound projector question for the gang...

[MovieStuff]

I was looking at a photo of a Bauer sound projector that had two sets of shutter blades. It was essentially a standard 3 bladed shutter but there was a second set of blades, slightly smaller in width, situated behind the first set. I am only surmising but I think what happens is that when the unit is running at 24/25fps, there are three shutter blade interruptions per frame because the smaller set of blades are hidden behind the larger set. When the unit is running at 18fps, the smaller set moves in between the larger set, effectively creating a 6 bladed shutter. The reason is the reduce the visible flicker to the eye by increasing the effective mechanical flicker rate. In other words, when the unit is running at 24/25fps, each frame of film "blinks" three times and then changes to the next frame but, because the shutter is spinning fast, the flicker of only three shutter blades isn't noticeable. When the unit is running slower at 18fps, which would normally make the image more "flickery" with only three blades, the additional blades make each frame of film "blink" 6 times and then changes to the next frame of film.

Does anyone here have one of these or have a manual to confirm? We want to add that 6 shutter blade option to the RetroSync software if that's the case.

Thanks!

[nikonr10]

Hi Roger ,

May be PM vaneck or send him email at http://shop.van-eck.net/PP-0012.html?_g ... ch=pp-0012

As he has many manuals !

Good to see that you are well after recent events

[MovieStuff]

I've looked at the manual and it says nothing about the shutter blades, which is odd. I can't find anything about them.

[MovieStuff]

Here's what the shutter blades look like:



Again, I think the smaller set moves in between the regular blades when the unit is in the 18fps mode. This would reduce the visible flicker by increasing the effective flicker rate to the eye. But I could be totally wrong. I will try emailing vaneck and see what he has to say.

Thanks for the tip.

Roger

[Jonathan]

Hi Roger,

the Bauer projector has a three bladed shutter at all frame rates. The extra set of blades is for reverse motion. In forward motion, the two sets of blades align, so the light output is maximized. In reverse motion, the smaller set of blades shifts a bit to create a longer dark interval. I believe this is because film transport is optimized for forward motion and it takes a bit longer for the frame to settle in the gate in reverse motion. Without the extra blades you would notice the frame jumping.

Best regards,

Jonathan.

[MovieStuff]

Hi Roger,

the Bauer projector has a three bladed shutter at all frame rates. The extra set of blades is for reverse motion. In forward motion, the two sets of blades align, so the light output is maximized. In reverse motion, the smaller set of blades shifts a bit to create a longer dark interval. I believe this is because film transport is optimized for forward motion and it takes a bit longer for the frame to settle in the gate in reverse motion. Without the extra blades you would notice the frame jumping.

Hmmm...... I have no reason to not believe you but I must say that's a rather arcane solution to a non problem on the part of Bauer. I can understand what you are saying, i.e. the film moves up in reverse and I'm guessing they found out after designing the claw/cam assembly that the film could be seen still in motion. So, rather than redesign the cam or just make the shutter blades slightly wider to cover that residual movement, they added a second set to slide into place in reverse. Weird. Not sure it's worth all the trouble but maybe the Bauer engineers were having a slow week or something.

Thanks for the information. Bizarre.

Roger

[MovieStuff]

Update on this mystery. This info from Van Eck:

In reverse the motor runs in the different direction, this means that the cooling from the fan is not reaching the part that burn the film. This is why in reverse the film is in more danger off burning.

With kind regards,
Thijs de Kort
Repair department
Van Eck Videoservices

So the extra blades act as a heat shield for the film in reverse. Makes sense. I’ve seen other projectors where a metal shield would drop in place in reverse. On some projectors reverse motion is achieved mechanical by way of gearing or pulleys. The motor remains forward but the mechanism runs backwards, like with a car engine/transmission so the gate and film still have positive cooling from the fan on the motor. On other projectors, the motor runs in reverse, thus changing the flow of air from the cooling fan.

Roger